diff --git a/apps/cloud_federation_api/appinfo/routes.php b/apps/cloud_federation_api/appinfo/routes.php
index 9dcffd0aa3489..189eb8c86c465 100644
--- a/apps/cloud_federation_api/appinfo/routes.php
+++ b/apps/cloud_federation_api/appinfo/routes.php
@@ -8,6 +8,11 @@
  */
 return [
 	'routes' => [
+		[
+			'name' => 'Token#jwks',
+			'url' => '/api/v1/jwks',
+			'verb' => 'GET',
+		],
 		[
 			'name' => 'RequestHandler#addShare',
 			'url' => '/shares',
diff --git a/apps/cloud_federation_api/lib/Controller/OCMRequestController.php b/apps/cloud_federation_api/lib/Controller/OCMRequestController.php
index 0907756602d42..6615e0256e6c3 100644
--- a/apps/cloud_federation_api/lib/Controller/OCMRequestController.php
+++ b/apps/cloud_federation_api/lib/Controller/OCMRequestController.php
@@ -9,7 +9,6 @@
 
 namespace OCA\CloudFederationAPI\Controller;
 
-use JsonException;
 use OCP\AppFramework\Controller;
 use OCP\AppFramework\Http;
 use OCP\AppFramework\Http\Attribute\BruteForceProtection;
@@ -18,6 +17,7 @@
 use OCP\AppFramework\Http\JSONResponse;
 use OCP\AppFramework\Http\Response;
 use OCP\EventDispatcher\IEventDispatcher;
+use OCP\Federation\ICloudFederationProviderManager;
 use OCP\IRequest;
 use OCP\OCM\Events\OCMEndpointRequestEvent;
 use OCP\OCM\Exceptions\OCMArgumentException;
@@ -31,6 +31,7 @@ public function __construct(
 		IRequest $request,
 		private readonly IEventDispatcher $eventDispatcher,
 		private readonly IOCMDiscoveryService $ocmDiscoveryService,
+		private readonly ICloudFederationProviderManager $cloudFederationProviderManager,
 		private readonly LoggerInterface $logger,
 	) {
 		parent::__construct($appName, $request);
@@ -56,10 +57,22 @@ public function manageOCMRequests(string $ocmPath): Response {
 			throw new OCMArgumentException('path is not UTF-8');
 		}
 
+		// Resolve the signer origin from the payload before verification.
+		$payload = $this->request->getParams();
+		$origin = null;
+		if ($payload !== []) {
+			$identity = $this->cloudFederationProviderManager->resolveSenderIdentity($payload);
+			if ($identity !== null) {
+				try {
+					$origin = $this->ocmDiscoveryService->getHostFromOcmAddress($identity);
+				} catch (IncomingRequestException) {
+					// unresolvable origin; verification will fail without one
+				}
+			}
+		}
+
 		try {
-			// if request is signed and well signed, no exceptions are thrown
-			// if request is not signed and host is known for not supporting signed request, no exceptions are thrown
-			$signedRequest = $this->ocmDiscoveryService->getIncomingSignedRequest();
+			$signedRequest = $this->ocmDiscoveryService->getIncomingSignedRequest($origin);
 		} catch (IncomingRequestException $e) {
 			$this->logger->warning('incoming ocm request exception', ['exception' => $e]);
 			$response = new JSONResponse(['message' => $e->getMessage(), 'validationErrors' => []], Http::STATUS_BAD_REQUEST);
@@ -67,15 +80,6 @@ public function manageOCMRequests(string $ocmPath): Response {
 			return $response;
 		}
 
-		// assuming that ocm request contains a json array
-		$payload = $signedRequest?->getBody() ?? file_get_contents('php://input');
-		try {
-			$payload = ($payload) ? json_decode($payload, true, 512, JSON_THROW_ON_ERROR) : null;
-		} catch (JsonException $e) {
-			$this->logger->debug('json decode error', ['exception' => $e]);
-			$payload = null;
-		}
-
 		$event = new OCMEndpointRequestEvent(
 			$this->request->getMethod(),
 			preg_replace('@/+@', '/', $ocmPath),
diff --git a/apps/cloud_federation_api/lib/Controller/RequestHandlerController.php b/apps/cloud_federation_api/lib/Controller/RequestHandlerController.php
index a855bb96206ca..f7a3a2c7e6d94 100644
--- a/apps/cloud_federation_api/lib/Controller/RequestHandlerController.php
+++ b/apps/cloud_federation_api/lib/Controller/RequestHandlerController.php
@@ -110,7 +110,8 @@ public function addShare($shareWith, $name, $description, $providerId, $owner, $
 			try {
 				// if request is signed and well signed, no exceptions are thrown
 				// if request is not signed and host is known for not supporting signed request, no exception are thrown
-				$signedRequest = $this->ocmDiscoveryService->getIncomingSignedRequest();
+				$origin = $this->ocmDiscoveryService->getHostFromOcmAddress($owner);
+				$signedRequest = $this->ocmDiscoveryService->getIncomingSignedRequest($origin);
 				$this->confirmSignedOrigin($signedRequest, 'owner', $owner);
 			} catch (IncomingRequestException $e) {
 				$this->logger->warning('incoming request exception', ['exception' => $e]);
@@ -307,10 +308,15 @@ public function receiveNotification($notificationType, $resourceType, $providerI
 
 		if (!$this->appConfig->getValueBool('core', OCMSignatoryManager::APPCONFIG_SIGN_DISABLED, lazy: true)) {
 			try {
-				// if request is signed and well signed, no exception are thrown
-				// if request is not signed and host is known for not supporting signed request, no exception are thrown
-				$signedRequest = $this->ocmDiscoveryService->getIncomingSignedRequest();
-				$this->confirmNotificationIdentity($signedRequest, $resourceType, $notification);
+				$identity = $this->resolveNotificationIdentity($resourceType, $notification);
+				$origin = null;
+				if ($identity !== '') {
+					$origin = $this->ocmDiscoveryService->getHostFromOcmAddress($identity);
+				}
+				$signedRequest = $this->ocmDiscoveryService->getIncomingSignedRequest($origin);
+				if ($identity !== '') {
+					$this->ocmDiscoveryService->confirmRequestOrigin($signedRequest?->getOrigin(), $identity);
+				}
 			} catch (IncomingRequestException $e) {
 				$this->logger->warning('incoming request exception', ['exception' => $e]);
 				return new JSONResponse(['message' => $e->getMessage(), 'validationErrors' => []], Http::STATUS_BAD_REQUEST);
@@ -450,22 +456,16 @@ private function confirmSignedOrigin(?IIncomingSignedRequest $signedRequest, str
 	}
 
 	/**
-	 *  confirm identity of the remote instance on notification, based on the share token.
+	 * Resolve the sender identity from a notification's sharedSecret.
+	 * Returns '' when the provider does not implement signed federation.
 	 *
-	 *  If request is not signed, we still verify that the hostname from the extracted value does,
-	 *  actually, not support signed request
-	 *
-	 * @param IIncomingSignedRequest|null $signedRequest
 	 * @param string $resourceType
+	 * @param array<string, mixed> $notification
 	 *
 	 * @throws IncomingRequestException
 	 * @throws BadRequestException
 	 */
-	private function confirmNotificationIdentity(
-		?IIncomingSignedRequest $signedRequest,
-		string $resourceType,
-		array $notification,
-	): void {
+	private function resolveNotificationIdentity(string $resourceType, array $notification): string {
 		$sharedSecret = $notification['sharedSecret'] ?? '';
 		if ($sharedSecret === '') {
 			throw new BadRequestException(['sharedSecret']);
@@ -481,14 +481,12 @@ private function confirmNotificationIdentity(
 					$mapping = Server::get(OcmTokenMapMapper::class)->getByAccessTokenId($accessTokenDb->getId());
 					$identity = $provider->getFederationIdFromSharedSecret($mapping->getRefreshToken(), $notification);
 				}
-			} else {
-				$this->logger->debug('cloud federation provider {provider} does not implements ISignedCloudFederationProvider', ['provider' => $provider::class]);
-				return;
+				return $identity;
 			}
+			$this->logger->debug('cloud federation provider {provider} does not implement ISignedCloudFederationProvider', ['provider' => $provider::class]);
 		} catch (\Exception $e) {
 			throw new IncomingRequestException($e->getMessage(), previous: $e);
 		}
-
-		$this->ocmDiscoveryService->confirmRequestOrigin($signedRequest?->getOrigin(), $identity);
+		return '';
 	}
 }
diff --git a/apps/cloud_federation_api/lib/Controller/TokenController.php b/apps/cloud_federation_api/lib/Controller/TokenController.php
index d62281f898a1b..31373c70b47f3 100644
--- a/apps/cloud_federation_api/lib/Controller/TokenController.php
+++ b/apps/cloud_federation_api/lib/Controller/TokenController.php
@@ -18,12 +18,14 @@
 use OCP\AppFramework\Http\Attribute\NoCSRFRequired;
 use OCP\AppFramework\Http\Attribute\PublicPage;
 use OCP\AppFramework\Http\DataResponse;
+use OCP\AppFramework\Http\JSONResponse;
 use OCP\AppFramework\Utility\ITimeFactory;
 use OCP\Authentication\Exceptions\ExpiredTokenException;
 use OCP\Authentication\Exceptions\InvalidTokenException;
 use OCP\Authentication\Token\IToken;
 use OCP\IAppConfig;
 use OCP\IRequest;
+use OCP\OCM\IOCMDiscoveryService;
 use OCP\Security\ISecureRandom;
 use OCP\Security\Signature\Exceptions\IncomingRequestException;
 use OCP\Security\Signature\Exceptions\SignatoryNotFoundException;
@@ -51,19 +53,44 @@ public function __construct(
 		private readonly IAppConfig $appConfig,
 		private readonly OcmTokenMapMapper $ocmTokenMapMapper,
 		private readonly IShareManager $shareManager,
+		private readonly IOCMDiscoveryService $ocmDiscoveryService,
 	) {
 		parent::__construct('cloud_federation_api', $request);
 	}
 
+	/**
+	 * Resolve the signer origin from the refresh token's share, or null.
+	 *
+	 * @param string $code refresh token
+	 * @return string|null signer origin, or null if it cannot be determined
+	 */
+	private function resolveOriginFromRefreshToken(string $code): ?string {
+		if ($code === '') {
+			return null;
+		}
+		try {
+			$share = $this->shareManager->getShareByToken($code);
+			$sharedWith = $share->getSharedWith();
+			if ($sharedWith === null || $sharedWith === '') {
+				return null;
+			}
+			return $this->ocmDiscoveryService->getHostFromOcmAddress($sharedWith);
+		} catch (\Throwable) {
+			return null;
+		}
+	}
+
 	/**
 	 * Verify the signature of incoming request if available
 	 *
+	 * @param string|null $origin the origin of the request, or null if unknown
+	 *
 	 * @return IIncomingSignedRequest|null null if remote does not support signed requests
 	 * @throws IncomingRequestException if signature is required but invalid
 	 */
-	private function verifySignedRequest(): ?IIncomingSignedRequest {
+	private function verifySignedRequest(?string $origin): ?IIncomingSignedRequest {
 		try {
-			$signedRequest = $this->signatureManager->getIncomingSignedRequest($this->signatoryManager);
+			$signedRequest = $this->signatureManager->getIncomingSignedRequest($this->signatoryManager, null, $origin);
 			$this->logger->debug('Token request signature verified', [
 				'origin' => $signedRequest->getOrigin()
 			]);
@@ -109,6 +136,27 @@ private function resolveJwtSigningKey(string $privateKeyPem): array {
 		throw new \RuntimeException('Unsupported signatory key type for JWT access token');
 	}
 
+	/**
+	 * Serve the local JWK Set
+	 *
+	 * @return JSONResponse<Http::STATUS_OK, array{keys: list<array<string, string>>}, array{}>
+	 *
+	 * 200: JWK Set returned
+	 */
+	#[PublicPage]
+	#[NoCSRFRequired]
+	public function jwks(): JSONResponse {
+		$keys = [];
+		try {
+			foreach ($this->signatoryManager->getLocalJwks() as $jwk) {
+				$keys[] = $jwk;
+			}
+		} catch (\Throwable $e) {
+			$this->logger->warning('failed to build local JWKs', ['exception' => $e]);
+		}
+		return new JSONResponse(['keys' => $keys]);
+	}
+
 	/**
 	 * Exchange a refresh token for a short-lived access token
 	 *
@@ -126,7 +174,7 @@ private function resolveJwtSigningKey(string $privateKeyPem): array {
 	#[FrontpageRoute(verb: 'POST', url: '/api/v1/access-token')]
 	public function accessToken(string $grant_type = '', string $code = ''): DataResponse {
 		try {
-			$signedRequest = $this->verifySignedRequest();
+			$signedRequest = $this->verifySignedRequest($this->resolveOriginFromRefreshToken($code));
 		} catch (IncomingRequestException $e) {
 			$this->logger->warning('Token request signature verification failed', [
 				'exception' => $e
diff --git a/apps/cloud_federation_api/openapi.json b/apps/cloud_federation_api/openapi.json
index 1f4a4e3a050c4..fffbefe54162b 100644
--- a/apps/cloud_federation_api/openapi.json
+++ b/apps/cloud_federation_api/openapi.json
@@ -323,13 +323,13 @@
         }
     },
     "tags": [
-        {
-            "name": "request_handler",
-            "description": "Open-Cloud-Mesh-API"
-        },
         {
             "name": "token",
             "description": "Controller for the /token endpoint Exchanges long-lived refresh tokens for short-lived access tokens"
+        },
+        {
+            "name": "request_handler",
+            "description": "Open-Cloud-Mesh-API"
         }
     ]
 }
diff --git a/apps/cloud_federation_api/tests/Controller/TokenControllerTest.php b/apps/cloud_federation_api/tests/Controller/TokenControllerTest.php
index 2506c673882d2..0fe6572f7a2ba 100644
--- a/apps/cloud_federation_api/tests/Controller/TokenControllerTest.php
+++ b/apps/cloud_federation_api/tests/Controller/TokenControllerTest.php
@@ -23,6 +23,7 @@
 use OCP\Authentication\Token\IToken;
 use OCP\IAppConfig;
 use OCP\IRequest;
+use OCP\OCM\IOCMDiscoveryService;
 use OCP\Security\ISecureRandom;
 use OCP\Security\Signature\Exceptions\SignatoryNotFoundException;
 use OCP\Security\Signature\Exceptions\SignatureException;
@@ -47,6 +48,7 @@ class TokenControllerTest extends TestCase {
 	private IAppConfig&MockObject $appConfig;
 	private OcmTokenMapMapper&MockObject $ocmTokenMapMapper;
 	private IShareManager&MockObject $shareManager;
+	private IOCMDiscoveryService&MockObject $ocmDiscoveryService;
 
 	private TokenController $controller;
 
@@ -67,6 +69,7 @@ protected function setUp(): void {
 		$this->appConfig = $this->createMock(IAppConfig::class);
 		$this->ocmTokenMapMapper = $this->createMock(OcmTokenMapMapper::class);
 		$this->shareManager = $this->createMock(IShareManager::class);
+		$this->ocmDiscoveryService = $this->createMock(IOCMDiscoveryService::class);
 
 		$this->controller = new TokenController(
 			$this->request,
@@ -79,6 +82,7 @@ protected function setUp(): void {
 			$this->appConfig,
 			$this->ocmTokenMapMapper,
 			$this->shareManager,
+			$this->ocmDiscoveryService,
 		);
 	}
 
diff --git a/core/AppInfo/Application.php b/core/AppInfo/Application.php
index 51425946a2536..52986a21f6471 100644
--- a/core/AppInfo/Application.php
+++ b/core/AppInfo/Application.php
@@ -38,7 +38,6 @@
 use OC\Core\Sharing\Recipient\TokenShareRecipientType;
 use OC\Core\Sharing\Recipient\UserShareRecipientType;
 use OC\OCM\OCMDiscoveryHandler;
-use OC\OCM\OCMJwksHandler;
 use OC\TagManager;
 use OCP\AppFramework\App;
 use OCP\AppFramework\Bootstrap\IBootContext;
@@ -110,7 +109,6 @@ public function register(IRegistrationContext $context): void {
 		$context->registerConfigLexicon(ConfigLexicon::class);
 
 		$context->registerWellKnownHandler(OCMDiscoveryHandler::class);
-		$context->registerWellKnownHandler(OCMJwksHandler::class);
 		$context->registerCapability(Capabilities::class);
 
 		$context->registerEventListener(RestrictInteractionEvent::class, RestrictInteractionListener::class);
diff --git a/lib/composer/composer/autoload_classmap.php b/lib/composer/composer/autoload_classmap.php
index beafb4700c69d..4f4de0ee036da 100644
--- a/lib/composer/composer/autoload_classmap.php
+++ b/lib/composer/composer/autoload_classmap.php
@@ -2047,7 +2047,6 @@
     'OC\\OCM\\Model\\OCMResource' => $baseDir . '/lib/private/OCM/Model/OCMResource.php',
     'OC\\OCM\\OCMDiscoveryHandler' => $baseDir . '/lib/private/OCM/OCMDiscoveryHandler.php',
     'OC\\OCM\\OCMDiscoveryService' => $baseDir . '/lib/private/OCM/OCMDiscoveryService.php',
-    'OC\\OCM\\OCMJwksHandler' => $baseDir . '/lib/private/OCM/OCMJwksHandler.php',
     'OC\\OCM\\OCMSignatoryManager' => $baseDir . '/lib/private/OCM/OCMSignatoryManager.php',
     'OC\\OCM\\Rfc9421SignatoryManager' => $baseDir . '/lib/private/OCM/Rfc9421SignatoryManager.php',
     'OC\\OCS\\ApiHelper' => $baseDir . '/lib/private/OCS/ApiHelper.php',
diff --git a/lib/composer/composer/autoload_static.php b/lib/composer/composer/autoload_static.php
index e024c1fb44b9f..0c02270a66a13 100644
--- a/lib/composer/composer/autoload_static.php
+++ b/lib/composer/composer/autoload_static.php
@@ -2088,7 +2088,6 @@ class ComposerStaticInit749170dad3f5e7f9ca158f5a9f04f6a2
         'OC\\OCM\\Model\\OCMResource' => __DIR__ . '/../../..' . '/lib/private/OCM/Model/OCMResource.php',
         'OC\\OCM\\OCMDiscoveryHandler' => __DIR__ . '/../../..' . '/lib/private/OCM/OCMDiscoveryHandler.php',
         'OC\\OCM\\OCMDiscoveryService' => __DIR__ . '/../../..' . '/lib/private/OCM/OCMDiscoveryService.php',
-        'OC\\OCM\\OCMJwksHandler' => __DIR__ . '/../../..' . '/lib/private/OCM/OCMJwksHandler.php',
         'OC\\OCM\\OCMSignatoryManager' => __DIR__ . '/../../..' . '/lib/private/OCM/OCMSignatoryManager.php',
         'OC\\OCM\\Rfc9421SignatoryManager' => __DIR__ . '/../../..' . '/lib/private/OCM/Rfc9421SignatoryManager.php',
         'OC\\OCS\\ApiHelper' => __DIR__ . '/../../..' . '/lib/private/OCS/ApiHelper.php',
diff --git a/lib/private/AppFramework/Http/Attributes/FederationRateLimit.php b/lib/private/AppFramework/Http/Attributes/FederationRateLimit.php
index 98930adceca48..412d951b3abfa 100644
--- a/lib/private/AppFramework/Http/Attributes/FederationRateLimit.php
+++ b/lib/private/AppFramework/Http/Attributes/FederationRateLimit.php
@@ -13,6 +13,7 @@
 use OC\OCM\OCMDiscoveryService;
 use OCA\Federation\TrustedServers;
 use OCP\AppFramework\Http\Attribute\AnonRateLimit;
+use OCP\Federation\ICloudFederationProviderManager;
 use OCP\IRequest;
 use OCP\Server;
 
@@ -24,12 +25,14 @@
  */
 #[Attribute(Attribute::TARGET_METHOD)]
 class FederationRateLimit extends AnonRateLimit {
+	private readonly ICloudFederationProviderManager $federationProviderManager;
 	private readonly OCMDiscoveryService $discoveryService;
 	private readonly ?TrustedServers $trustedServers;
 
 	public function __construct(int $limit, int $period) {
 		parent::__construct($limit, $period);
 
+		$this->federationProviderManager = Server::get(ICloudFederationProviderManager::class);
 		$this->discoveryService = Server::get(OCMDiscoveryService::class);
 		$this->trustedServers = Server::get(TrustedServers::class);
 	}
@@ -41,14 +44,22 @@ public function shouldApply(IRequest $request): bool {
 		}
 
 		try {
-			$signedRequest = $this->discoveryService->getIncomingSignedRequest();
+			// Resolve the signer origin from the payload so trusted servers
+			// can be exempted.
+			$parsed = $request->getParams();
+			$identity = $this->federationProviderManager->resolveSenderIdentity($parsed);
+			$origin = null;
+			if ($identity !== null) {
+				$origin = $this->discoveryService->getHostFromOcmAddress($identity);
+			}
+
+			$signedRequest = $this->discoveryService->getIncomingSignedRequest($origin);
 			if (!$signedRequest) {
 				return true;
 			}
-			$signedRequest->verify();
 			return !$this->trustedServers->isTrustedServer($signedRequest->getOrigin());
 		} catch (\Exception) {
-			// no or invalid signature
+			// no or invalid signature, or unresolvable origin
 			return true;
 		}
 	}
diff --git a/lib/private/Federation/CloudFederationProviderManager.php b/lib/private/Federation/CloudFederationProviderManager.php
index a0bafa84c997f..3db68b9c16a9f 100644
--- a/lib/private/Federation/CloudFederationProviderManager.php
+++ b/lib/private/Federation/CloudFederationProviderManager.php
@@ -18,6 +18,7 @@
 use OCP\Federation\ICloudFederationProviderManager;
 use OCP\Federation\ICloudFederationShare;
 use OCP\Federation\ICloudIdManager;
+use OCP\Federation\ISignedCloudFederationProvider;
 use OCP\Http\Client\IClient;
 use OCP\Http\Client\IClientService;
 use OCP\Http\Client\IResponse;
@@ -105,6 +106,39 @@ public function getCloudFederationProvider($resourceType) {
 		}
 	}
 
+	/**
+	 * @inheritDoc
+	 *
+	 * Notifications resolve via sharedSecret; shares via owner/sender.
+	 */
+	#[\Override]
+	public function resolveSenderIdentity(array $body): ?string {
+		$resourceType = $body['resourceType'] ?? '';
+		if ($resourceType !== '') {
+			$notification = $body['notification'] ?? null;
+			$sharedSecret = is_array($notification) ? ($notification['sharedSecret'] ?? '') : '';
+			if ($sharedSecret !== '') {
+				try {
+					$provider = $this->getCloudFederationProvider($resourceType);
+					if ($provider instanceof ISignedCloudFederationProvider || $provider instanceof \NCU\Federation\ISignedCloudFederationProvider) {
+						$identity = $provider->getFederationIdFromSharedSecret($sharedSecret, is_array($notification) ? $notification : []);
+						if ($identity !== '') {
+							return $identity;
+						}
+					}
+				} catch (\Exception) {
+					// unresolved; fall through to share-style fields
+				}
+			}
+		}
+		foreach (['owner', 'sender', 'sharedBy'] as $field) {
+			if (isset($body[$field]) && is_string($body[$field]) && $body[$field] !== '') {
+				return $body[$field];
+			}
+		}
+		return null;
+	}
+
 	/**
 	 * @deprecated 29.0.0 - Use {@see sendCloudShare()} instead and handle errors manually
 	 */
diff --git a/lib/private/OCM/Model/OCMProvider.php b/lib/private/OCM/Model/OCMProvider.php
index 76530353613c4..16ec74890e80f 100644
--- a/lib/private/OCM/Model/OCMProvider.php
+++ b/lib/private/OCM/Model/OCMProvider.php
@@ -26,6 +26,7 @@ class OCMProvider implements IOCMProvider {
 	private array $capabilities = [];
 	private string $endPoint = '';
 	private string $tokenEndPoint = '';
+	private string $jwksUri = '';
 	/** @var IOCMResource[] */
 	private array $resourceTypes = [];
 	private ?Signatory $signatory = null;
@@ -144,6 +145,26 @@ public function getTokenEndPoint(): string {
 		return '';
 	}
 
+	/**
+	 * @param string $jwksUri
+	 *
+	 * @return $this
+	 */
+	#[\Override]
+	public function setJwksUri(string $jwksUri): static {
+		$this->jwksUri = $jwksUri;
+
+		return $this;
+	}
+
+	/**
+	 * @return string
+	 */
+	#[\Override]
+	public function getJwksUri(): string {
+		return $this->jwksUri;
+	}
+
 	/**
 	 * @return string
 	 */
@@ -311,6 +332,9 @@ public function import(array $data): static {
 		if (isset($data['tokenEndPoint'])) {
 			$this->setTokenEndPoint($data['tokenEndPoint']);
 		}
+		if (is_string($data['jwksUri'] ?? null)) {
+			$this->setJwksUri($data['jwksUri']);
+		}
 
 		if (!$this->looksValid()) {
 			throw new OCMProviderException('remote provider does not look valid');
@@ -357,6 +381,10 @@ public function jsonSerialize(): array {
 		if ($inviteAcceptDialog !== '') {
 			$response['inviteAcceptDialog'] = $inviteAcceptDialog;
 		}
+		$jwksUri = $this->getJwksUri();
+		if ($jwksUri !== '') {
+			$response['jwksUri'] = $jwksUri;
+		}
 		return $response;
 	}
 }
diff --git a/lib/private/OCM/OCMDiscoveryService.php b/lib/private/OCM/OCMDiscoveryService.php
index 9975038f33321..dbe741da55e7f 100644
--- a/lib/private/OCM/OCMDiscoveryService.php
+++ b/lib/private/OCM/OCMDiscoveryService.php
@@ -209,7 +209,13 @@ public function getLocalOCMProvider(bool $fullDetails = true): IOCMProvider {
 		$provider->setCapabilities(['notifications', 'shares', 'exchange-token']);
 		$provider->setTokenEndPoint($tokenUrl);
 		if ($signingEnabled) {
-			$provider->setCapabilities(['http-sig']);
+			try {
+				// http-sig advertisement requires a jwksUri
+				$provider->setJwksUri($this->signatoryManager->getLocalJwksUri());
+				$provider->setCapabilities(['http-sig']);
+			} catch (IdentityNotFoundException $e) {
+				$this->logger->warning('cannot build local jwksUri, http-sig capability not advertised', ['exception' => $e]);
+			}
 		}
 
 		$resource = $provider->createNewResourceType();
@@ -253,9 +259,9 @@ public function getLocalOCMProvider(bool $fullDetails = true): IOCMProvider {
 	 * @since 33.0.0
 	 */
 	#[\Override]
-	public function getIncomingSignedRequest(): ?IIncomingSignedRequest {
+	public function getIncomingSignedRequest(?string $origin = null): ?IIncomingSignedRequest {
 		try {
-			$signedRequest = $this->signatureManager->getIncomingSignedRequest($this->signatoryManager);
+			$signedRequest = $this->signatureManager->getIncomingSignedRequest($this->signatoryManager, null, $origin);
 			$this->logger->debug('signed request available', ['signedRequest' => $signedRequest]);
 			return $signedRequest;
 		} catch (SignatureNotFoundException|SignatoryNotFoundException $e) {
@@ -277,7 +283,7 @@ public function getIncomingSignedRequest(): ?IIncomingSignedRequest {
 	/**
 	 * @inheritDoc
 	 *
-	 * @since 34.0.0
+	 * @since 35.0.0
 	 */
 	#[\Override]
 	public function confirmRequestOrigin(?string $signedOrigin, string $ocmAddress): void {
@@ -304,9 +310,14 @@ public function confirmRequestOrigin(?string $signedOrigin, string $ocmAddress):
 	}
 
 	/**
+	 * Extract the signer origin (host) from an OCM address (`user@host`).
+	 *
+	 * @param string $entry OCM address in `user@host` or `user@https://host` form
+	 * @return string the host (with port) of the OCM address
 	 * @throws IncomingRequestException on malformed address or unresolvable host
 	 */
-	private function getHostFromOcmAddress(string $entry): string {
+	#[\Override]
+	public function getHostFromOcmAddress(string $entry): string {
 		try {
 			$cloudId = $this->cloudIdManager->resolveCloudId(trim($entry, '@'));
 			return $this->signatureManager->extractIdentityFromUri($cloudId->getRemote());
diff --git a/lib/private/OCM/OCMJwksHandler.php b/lib/private/OCM/OCMJwksHandler.php
deleted file mode 100644
index 0013b38b1b400..0000000000000
--- a/lib/private/OCM/OCMJwksHandler.php
+++ /dev/null
@@ -1,49 +0,0 @@
-<?php
-
-declare(strict_types=1);
-
-/**
- * SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
- * SPDX-License-Identifier: AGPL-3.0-or-later
- */
-
-namespace OC\OCM;
-
-use OCP\AppFramework\Http\JSONResponse;
-use OCP\Http\WellKnown\GenericResponse;
-use OCP\Http\WellKnown\IHandler;
-use OCP\Http\WellKnown\IRequestContext;
-use OCP\Http\WellKnown\IResponse;
-use OCP\IAppConfig;
-use Psr\Log\LoggerInterface;
-use Throwable;
-
-/** Serves `/.well-known/jwks.json` (RFC 7517) with the OCM signing keys. */
-class OCMJwksHandler implements IHandler {
-	public function __construct(
-		private readonly IAppConfig $appConfig,
-		private readonly OCMSignatoryManager $signatoryManager,
-		private readonly LoggerInterface $logger,
-	) {
-	}
-
-	#[\Override]
-	public function handle(string $service, IRequestContext $context, ?IResponse $previousResponse): ?IResponse {
-		if ($service !== 'jwks.json') {
-			return $previousResponse;
-		}
-
-		$keys = [];
-		if (!$this->appConfig->getValueBool('core', OCMSignatoryManager::APPCONFIG_SIGN_DISABLED, lazy: true)) {
-			try {
-				foreach ($this->signatoryManager->getLocalJwks() as $jwk) {
-					$keys[] = $jwk;
-				}
-			} catch (Throwable $e) {
-				$this->logger->warning('failed to build local JWKs', ['exception' => $e]);
-			}
-		}
-
-		return new GenericResponse(new JSONResponse(['keys' => $keys]));
-	}
-}
diff --git a/lib/private/OCM/OCMSignatoryManager.php b/lib/private/OCM/OCMSignatoryManager.php
index 8320671456a12..433dac293e0a4 100644
--- a/lib/private/OCM/OCMSignatoryManager.php
+++ b/lib/private/OCM/OCMSignatoryManager.php
@@ -23,10 +23,12 @@
 use OCP\IConfig;
 use OCP\IURLGenerator;
 use OCP\OCM\Exceptions\OCMProviderException;
+use OCP\OCM\IOCMDiscoveryService;
 use OCP\Security\Signature\Enum\DigestAlgorithm;
 use OCP\Security\Signature\Enum\SignatoryType;
 use OCP\Security\Signature\Enum\SignatureAlgorithm;
 use OCP\Security\Signature\Exceptions\IdentityNotFoundException;
+use OCP\Security\Signature\Exceptions\SignatureException;
 use OCP\Security\Signature\ISignatureManager;
 use OCP\Security\Signature\Model\Signatory;
 use OCP\Server;
@@ -373,31 +375,36 @@ private function signatoryFromPool(int $poolId): ?Signatory {
 		return $signatory;
 	}
 
+	/** Absolute URL of the local JWK Set, advertised as `jwksUri`. */
+	public function getLocalJwksUri(): string {
+		return $this->urlGenerator->linkToRouteAbsolute('cloud_federation_api.Token.jwks');
+	}
+
 	/**
 	 * @param string $fragment URL fragment (e.g. 'signature' for cavage, 'ecdsa-p256-sha256' for the JWKS-published key)
 	 * @return string
 	 * @throws IdentityNotFoundException
 	 */
 	private function buildLocalKeyId(string $fragment): string {
+		return $this->buildLocalUrl('/ocm#' . $fragment);
+	}
+
+	/**
+	 * Absolute local URL for a signing path (keyId fragment or jwksUri),
+	 * built via {@see IURLGenerator::getAbsoluteURL()} so the advertised
+	 * signing origin matches the instance URL used for federated shares.
+	 * keyId callers re-canonicalize to https through {@see Signatory::setKeyId}.
+	 *
+	 * @param string $path absolute path, starting with a slash
+	 * @return string
+	 */
+	private function buildLocalUrl(string $path): string {
 		if ($this->appConfig->hasKey('core', self::APPCONFIG_SIGN_IDENTITY_EXTERNAL, true)) {
 			$identity = $this->appConfig->getValueString('core', self::APPCONFIG_SIGN_IDENTITY_EXTERNAL, lazy: true);
-			return 'https://' . $identity . '/ocm#' . $fragment;
+			return 'https://' . $identity . $path;
 		}
 
-		try {
-			return $this->signatureManager->generateKeyIdFromConfig('/ocm#' . $fragment);
-		} catch (IdentityNotFoundException) {
-		}
-
-		$url = $this->urlGenerator->linkToRouteAbsolute('cloud_federation_api.requesthandlercontroller.addShare');
-		$identity = $this->signatureManager->extractIdentityFromUri($url);
-
-		// catching possible subfolder to create a keyId like 'https://hostname/subfolder/ocm#<fragment>'
-		$path = parse_url($url, PHP_URL_PATH);
-		$pos = strpos($path, '/ocm/shares');
-		$sub = ($pos) ? substr($path, 0, $pos) : '';
-
-		return 'https://' . $identity . $sub . '/ocm#' . $fragment;
+		return $this->urlGenerator->getAbsoluteURL($path);
 	}
 
 	/**
@@ -476,10 +483,16 @@ private function readCachedJwks(string $origin): ?array {
 	}
 
 	/**
+	 * Fetch the peer's JWK Set from the URL advertised in the `jwksUri`
+	 * field of its discovery response.
+	 *
 	 * @return list<array<string, mixed>>|null
 	 */
 	private function fetchJwks(string $origin): ?array {
-		$url = 'https://' . $origin . '/.well-known/jwks.json';
+		$url = $this->resolveJwksUri($origin);
+		if ($url === null) {
+			return null;
+		}
 		$options = [
 			'timeout' => 10,
 			'connect_timeout' => 10,
@@ -508,6 +521,35 @@ private function fetchJwks(string $origin): ?array {
 		return array_values(array_filter($decoded['keys'], 'is_array'));
 	}
 
+	/**
+	 * The peer's `jwksUri` from its discovery response. Must be https, or
+	 * http from an http-only peer (the spec's testing fallback): an https
+	 * peer pointing at an http jwksUri would downgrade the key fetch.
+	 */
+	private function resolveJwksUri(string $origin): ?string {
+		try {
+			$provider = Server::get(IOCMDiscoveryService::class)->discover($origin);
+		} catch (NotFoundExceptionInterface|ContainerExceptionInterface|OCMProviderException $e) {
+			$this->logger->warning('cannot discover remote OCM provider for JWKS', ['exception' => $e, 'origin' => $origin]);
+			return null;
+		}
+
+		$jwksUri = $provider->getJwksUri();
+		if ($jwksUri === '') {
+			if ($provider->hasCapability('http-sig')) {
+				$this->logger->warning('remote advertises http-sig but no jwksUri; non-conformant peer', ['origin' => $origin]);
+			}
+			return null;
+		}
+		$httpFromHttpPeer = str_starts_with($jwksUri, 'http://')
+			&& str_starts_with($provider->getEndPoint(), 'http://');
+		if (!str_starts_with($jwksUri, 'https://') && !$httpFromHttpPeer) {
+			$this->logger->warning('refusing jwksUri: https is required unless the peer itself is http-only', ['origin' => $origin, 'jwksUri' => $jwksUri]);
+			return null;
+		}
+		return $jwksUri;
+	}
+
 	/**
 	 * @param list<array<string, mixed>>|null $keys
 	 */
@@ -519,8 +561,25 @@ private function findKid(?array $keys, string $keyId): ?Key {
 			if (($entry['kid'] ?? null) !== $keyId) {
 				continue;
 			}
+			// every published JWK must carry an `alg` parameter naming an
+			// acceptable asymmetric signature algorithm; keys without one
+			// are rejected as non-conformant
+			$alg = $entry['alg'] ?? null;
+			if (!is_string($alg) || $alg === '') {
+				$this->logger->warning('remote JWK carries no alg parameter', ['kid' => $keyId]);
+				return null;
+			}
 			try {
-				return JWK::parseKey($entry, Algorithm::deriveJoseAlgFromJwk($entry));
+				$native = Algorithm::normalize($alg);
+				$derived = Algorithm::deriveJoseAlgFromJwk($entry);
+				if ($derived !== null && Algorithm::normalize($derived) !== $native) {
+					$this->logger->warning('remote JWK alg does not match its key type', ['kid' => $keyId, 'alg' => $alg]);
+					return null;
+				}
+				return JWK::parseKey($entry);
+			} catch (SignatureException $e) {
+				$this->logger->warning('remote JWK alg is not acceptable', ['exception' => $e, 'kid' => $keyId, 'alg' => $alg]);
+				return null;
 			} catch (Throwable $e) {
 				$this->logger->warning('failed to parse remote JWK', ['exception' => $e, 'kid' => $keyId]);
 				return null;
diff --git a/lib/private/Security/Signature/Model/Rfc9421IncomingSignedRequest.php b/lib/private/Security/Signature/Model/Rfc9421IncomingSignedRequest.php
index 3697c156ec82b..89649d3bbe3a1 100644
--- a/lib/private/Security/Signature/Model/Rfc9421IncomingSignedRequest.php
+++ b/lib/private/Security/Signature/Model/Rfc9421IncomingSignedRequest.php
@@ -23,39 +23,42 @@
 use OC\Security\Signature\Rfc9421\SignatureBase;
 use OC\Security\Signature\SignatureManager;
 use OCP\IRequest;
-use OCP\Security\Signature\Exceptions\IdentityNotFoundException;
 use OCP\Security\Signature\Exceptions\IncomingRequestException;
 use OCP\Security\Signature\Exceptions\InvalidSignatureException;
 use OCP\Security\Signature\Exceptions\SignatoryNotFoundException;
 use OCP\Security\Signature\Exceptions\SignatureException;
 use OCP\Security\Signature\Exceptions\SignatureNotFoundException;
 use OCP\Security\Signature\IIncomingSignedRequest;
-use OCP\Security\Signature\Model\Signatory;
 
 /**
  * RFC 9421 implementation of {@see IIncomingSignedRequest}. Parses the
- * inbound Signature-Input / Signature dictionaries, picks the OCM-labeled
- * entry (RFC 9421 §3.2 lets verifiers scope by policy), and rebuilds the
- * signature base per RFC 9421 §2.5. Crypto is deferred to {@see verify()},
- * which needs a {@see Key} attached via {@see setKey()}. Body integrity
- * (RFC 9530 content-digest) is checked before verify() if covered.
+ * inbound Signature-Input / Signature dictionaries, picks the single entry
+ * carrying the `tag="ocm"` signature parameter (disregarding dictionary
+ * labels, as mandated by the OCM spec), and rebuilds the signature base per
+ * RFC 9421 §2.5. Crypto is deferred to {@see verify()}, which needs a
+ * {@see Key} attached via {@see setKey()}. Body integrity (RFC 9530
+ * content-digest) is checked before verify() if covered.
  */
 class Rfc9421IncomingSignedRequest extends SignedRequest implements
 	IIncomingSignedRequest,
 	JsonSerializable {
-	/** Baseline cover for OCM. Override via `rfc9421.requiredComponents`. */
-	private const DEFAULT_REQUIRED_COMPONENTS = [
+	/**
+	 * Baseline cover for OCM. Override via `rfc9421.requiredComponents`.
+	 * The `Date` header is deliberately not part of the required set:
+	 * freshness is anchored on the `created` signature parameter.
+	 */
+	public const REQUIRED_COMPONENTS = [
 		'@method',
 		'@target-uri',
 		'content-digest',
 		'content-length',
-		'date',
 	];
 
 	/** Max clock skew (seconds) for `created`. Override via `rfc9421.maxClockSkew`. */
 	private const DEFAULT_MAX_FUTURE_SKEW = 60;
 
 	private string $origin = '';
+	private string $label;
 	/** @var list<string> */
 	private array $components;
 	/** @var array<string, scalar> */
@@ -88,26 +91,42 @@ public function __construct(
 		$inputs = self::parseSignatureInput($signatureInputHeader);
 		$signatures = self::parseSignature($signatureHeader);
 
-		// OCM policy (stricter than RFC 8941 §4.2 last-wins): a duplicate
-		// `ocm` entry is ambiguous; the entire request MUST be rejected.
-		if (self::countLabel($signatureInputHeader, 'ocm') > 1
-			|| self::countLabel($signatureHeader, 'ocm') > 1) {
+		// The OCM signature is identified by its integrity-protected
+		// `tag="ocm"` parameter, disregarding dictionary labels. A message
+		// carrying more than one such signature MUST be rejected; one
+		// without any is unsigned as far as OCM is concerned.
+		$tagged = [];
+		foreach ($inputs as $label => $entry) {
+			if (($entry['params']['tag'] ?? null) === 'ocm') {
+				$tagged[] = $label;
+			}
+		}
+		if (count($tagged) > 1) {
+			throw new IncomingRequestException('multiple signatures carrying tag="ocm" in Signature-Input');
+		}
+		if ($tagged === []) {
+			throw new SignatureNotFoundException('no signature carrying tag="ocm" in Signature-Input');
+		}
+		$this->label = $tagged[0];
+
+		// A duplicated dictionary label is collapsed to its last entry by
+		// RFC 8941 §4.2 parsing; that ambiguity on the OCM entry is
+		// rejected outright.
+		if (self::countLabel($signatureInputHeader, $this->label) > 1
+			|| self::countLabel($signatureHeader, $this->label) > 1) {
 			throw new IncomingRequestException(
-				'multiple "' . 'ocm' . '" entries in signature headers'
+				'multiple "' . $this->label . '" entries in signature headers'
 			);
 		}
 
-		if (!isset($inputs['ocm'])) {
-			throw new SignatureNotFoundException('missing "' . 'ocm' . '" entry in Signature-Input');
-		}
-		if (!isset($signatures['ocm'])) {
-			throw new SignatureNotFoundException('missing "' . 'ocm' . '" entry in Signature');
+		if (!isset($signatures[$this->label])) {
+			throw new IncomingRequestException('missing "' . $this->label . '" entry in Signature');
 		}
 
-		$entry = $inputs['ocm'];
+		$entry = $inputs[$this->label];
 		$this->components = $entry['components'];
 		$this->signatureParams = $entry['params'];
-		$this->rawSignature = $signatures['ocm'];
+		$this->rawSignature = $signatures[$this->label];
 
 		$this->verifyRequiredComponents();
 		$this->verifyTimestamps();
@@ -118,13 +137,7 @@ public function __construct(
 		if (!is_string($keyId) || $keyId === '') {
 			throw new IncomingRequestException('missing keyid in Signature-Input');
 		}
-		try {
-			$this->origin = Signatory::extractIdentityFromUri($keyId);
-		} catch (IdentityNotFoundException) {
-			// keyid may follow the OCM convention `<fqdn>#<id>`; the OCM layer
-			// derives origin from the message body in that case.
-			$this->origin = '';
-		}
+		// keyid is opaque; the signer origin is set by the caller via setOrigin().
 
 		$paramsLine = SignatureBase::serializeSignatureParams($this->components, $this->signatureParams);
 		$this->signatureBaseString = SignatureBase::build(
@@ -136,7 +149,7 @@ public function __construct(
 		);
 
 		$this->setSigningElements([
-			'label' => 'ocm',
+			'label' => $this->label,
 			'keyId' => $keyId,
 			'algorithm' => isset($this->signatureParams['alg']) ? (string)$this->signatureParams['alg'] : '',
 			'created' => isset($this->signatureParams['created']) ? (string)$this->signatureParams['created'] : '',
@@ -161,6 +174,15 @@ public function getOrigin(): string {
 		return $this->origin;
 	}
 
+	/**
+	 * Signer origin, established by the caller from the share/sender identity.
+	 *
+	 * @param string $origin
+	 */
+	public function setOrigin(string $origin): void {
+		$this->origin = $origin;
+	}
+
 	#[\Override]
 	public function getKeyId(): string {
 		return $this->getSigningElement('keyId');
@@ -222,7 +244,7 @@ public function verify(): void {
 	/** @throws IncomingRequestException if the signature doesn't cover the OCM-required components */
 	private function verifyRequiredComponents(): void {
 		/** @var list<string> $required */
-		$required = $this->options['rfc9421.requiredComponents'] ?? self::DEFAULT_REQUIRED_COMPONENTS;
+		$required = $this->options['rfc9421.requiredComponents'] ?? self::REQUIRED_COMPONENTS;
 		$missing = array_values(array_diff($required, $this->components));
 		if ($missing !== []) {
 			throw new IncomingRequestException(
@@ -320,7 +342,7 @@ public function jsonSerialize(): array {
 			parent::jsonSerialize(),
 			[
 				'origin' => $this->origin,
-				'label' => 'ocm',
+				'label' => $this->label,
 				'components' => $this->components,
 				'signatureParams' => $this->signatureParams,
 				'signatureBase' => $this->signatureBaseString,
diff --git a/lib/private/Security/Signature/Model/Rfc9421OutgoingSignedRequest.php b/lib/private/Security/Signature/Model/Rfc9421OutgoingSignedRequest.php
index d2fa2a4ae86a3..812d24213dff7 100644
--- a/lib/private/Security/Signature/Model/Rfc9421OutgoingSignedRequest.php
+++ b/lib/private/Security/Signature/Model/Rfc9421OutgoingSignedRequest.php
@@ -25,7 +25,8 @@
  * RFC 9421 implementation of {@see IOutgoingSignedRequest}, sibling to the
  * draft-cavage {@see OutgoingSignedRequest}. Default ECDSA P-256 (`ES256`)
  * with the `alg` parameter omitted (RFC 9421 §3.3.7); verifier resolves it
- * from the JWK.
+ * from the JWK. The signature carries the `tag="ocm"` parameter mandated by
+ * the OCM spec; the `ocm` dictionary label is cosmetic.
  *
  * Options from {@see ISignatoryManager::getOptions()}: `rfc9421.signingAlgorithm`,
  * `rfc9421.coveredComponents`, `rfc9421.contentDigestAlgorithm`,
@@ -34,7 +35,6 @@
 class Rfc9421OutgoingSignedRequest extends SignedRequest implements
 	IOutgoingSignedRequest,
 	JsonSerializable {
-	private const DEFAULT_COMPONENTS = ['@method', '@target-uri', 'content-digest', 'content-length', 'date'];
 
 	private string $host = '';
 	private array $headers = [];
@@ -64,7 +64,7 @@ public function __construct(
 		$this->signingAlgorithm = (string)($options['rfc9421.signingAlgorithm'] ?? 'ecdsa-p256-sha256');
 		$contentDigestAlgorithm = (string)($options['rfc9421.contentDigestAlgorithm'] ?? ContentDigest::ALGO_SHA256);
 		/** @var list<string> $components */
-		$components = $options['rfc9421.coveredComponents'] ?? self::DEFAULT_COMPONENTS;
+		$components = $options['rfc9421.coveredComponents'] ?? Rfc9421IncomingSignedRequest::REQUIRED_COMPONENTS;
 		$includeAlg = (bool)($options['rfc9421.includeAlgParameter'] ?? false);
 		$dateHeaderFormat = (string)($options['dateHeader'] ?? SignatureManager::DATE_HEADER);
 
@@ -84,6 +84,9 @@ public function __construct(
 			// Off by default per RFC 9421 §3.3.7 (verifier resolves alg from JWK).
 			$this->signatureParams['alg'] = $this->signingAlgorithm;
 		}
+		// integrity-protected marker (RFC 9421 §2.3) identifying this
+		// signature as the OCM one; the dictionary label is not significant
+		$this->signatureParams['tag'] = 'ocm';
 
 		$this->signatureBaseString = SignatureBase::build(
 			$this->method,
diff --git a/lib/private/Security/Signature/Rfc9421/Algorithm.php b/lib/private/Security/Signature/Rfc9421/Algorithm.php
index 4fd7569a1ff12..3c79cd6721d75 100644
--- a/lib/private/Security/Signature/Rfc9421/Algorithm.php
+++ b/lib/private/Security/Signature/Rfc9421/Algorithm.php
@@ -110,7 +110,8 @@ public static function verify(string $signatureBase, string $signature, Key $key
 	}
 
 	/**
-	 * Map a JOSE alg (RFC 7518/8037) to the RFC 9421 native identifier.
+	 * Map a JOSE alg (RFC 7518/8037, including fully-specified RFC 9864
+	 * names such as `Ed25519`) to the RFC 9421 native identifier.
 	 * Pass-through if already native.
 	 *
 	 * @throws SignatureException
@@ -132,9 +133,9 @@ public static function normalize(string $algorithm): string {
 	}
 
 	/**
-	 * Default JOSE alg for {@see \Firebase\JWT\JWK::parseKey} when the JWK has
-	 * no `alg` (RFC 7517 leaves it optional). Null if kty/crv don't pin one
-	 * down (e.g. RSA, where the hash isn't determined).
+	 * JOSE alg implied by a JWK's kty/crv, used to cross-check the JWK's
+	 * mandatory `alg` member against its key material. Null if kty/crv
+	 * don't pin one down (e.g. RSA, where the hash isn't determined).
 	 *
 	 * @param array<string, mixed> $jwk
 	 */
diff --git a/lib/private/Security/Signature/SignatureManager.php b/lib/private/Security/Signature/SignatureManager.php
index 555ff28e1a337..efdf30e7b186f 100644
--- a/lib/private/Security/Signature/SignatureManager.php
+++ b/lib/private/Security/Signature/SignatureManager.php
@@ -97,6 +97,7 @@ public function __construct(
 	public function getIncomingSignedRequest(
 		ISignatoryManager $signatoryManager,
 		?string $body = null,
+		?string $origin = null,
 	): IIncomingSignedRequest {
 		$body = $body ?? file_get_contents('php://input');
 		$options = $signatoryManager->getOptions();
@@ -106,7 +107,7 @@ public function getIncomingSignedRequest(
 
 		// `Signature-Input` is unique to RFC 9421; cavage uses `Signature` only.
 		if ($this->request->getHeader('Signature-Input') !== '') {
-			return $this->getRfc9421IncomingSignedRequest($signatoryManager, $body, $options);
+			return $this->getRfc9421IncomingSignedRequest($signatoryManager, $body, $options, $origin);
 		}
 
 		// generate IncomingSignedRequest based on body and request
@@ -132,6 +133,11 @@ public function getIncomingSignedRequest(
 	/**
 	 * RFC 9421 inbound path. Requires {@see IJwkResolvingSignatoryManager}.
 	 *
+	 * @param ISignatoryManager $signatoryManager
+	 * @param string $body request body
+	 * @param array $options signatory manager options
+	 * @param string|null $origin signer origin from the caller (the keyid is opaque)
+	 *
 	 * @throws IncomingRequestException
 	 * @throws SignatureException
 	 * @throws SignatureNotFoundException
@@ -140,17 +146,25 @@ private function getRfc9421IncomingSignedRequest(
 		ISignatoryManager $signatoryManager,
 		string $body,
 		array $options,
+		?string $origin,
 	): IIncomingSignedRequest {
 		if (!($signatoryManager instanceof IJwkResolvingSignatoryManager)) {
 			throw new IncomingRequestException('RFC 9421 inbound is not supported by ' . get_class($signatoryManager));
 		}
+		if ($origin === null || $origin === '') {
+			// The keyid is opaque; the caller must supply the signer origin.
+			throw new IncomingRequestException('RFC 9421 verification requires the sender origin');
+		}
 
 		$signedRequest = new Rfc9421IncomingSignedRequest($body, $this->request, $options);
+		$signedRequest->setOrigin($origin);
 
 		try {
 			$key = $signatoryManager->getRemoteKey($signedRequest->getOrigin(), $signedRequest->getKeyId());
 			if ($key === null) {
-				throw new SignatoryNotFoundException('no JWK resolved for keyid ' . $signedRequest->getKeyId());
+				// a present signature MUST be verified; an unresolvable key
+				// is a verification failure, not an unsigned request
+				throw new IncomingRequestException('no JWK resolved for keyid ' . $signedRequest->getKeyId());
 			}
 			$signedRequest->setKey($key);
 			$signedRequest->verify();
diff --git a/lib/public/Federation/ICloudFederationProviderManager.php b/lib/public/Federation/ICloudFederationProviderManager.php
index 815808ffa4189..2bf2ba1ac738a 100644
--- a/lib/public/Federation/ICloudFederationProviderManager.php
+++ b/lib/public/Federation/ICloudFederationProviderManager.php
@@ -60,6 +60,15 @@ public function getAllCloudFederationProviders();
 	 */
 	public function getCloudFederationProvider($resourceType);
 
+	/**
+	 * Resolve the sender's federated identity from an OCM request body.
+	 *
+	 * @param array $body decoded OCM request body
+	 * @return string|null federated cloud id (`user@host`), or null
+	 * @since 35.0.0
+	 */
+	public function resolveSenderIdentity(array $body): ?string;
+
 	/**
 	 * send federated share
 	 *
diff --git a/lib/public/OCM/IOCMDiscoveryService.php b/lib/public/OCM/IOCMDiscoveryService.php
index 674c907bb1587..68855c59b0652 100644
--- a/lib/public/OCM/IOCMDiscoveryService.php
+++ b/lib/public/OCM/IOCMDiscoveryService.php
@@ -59,11 +59,14 @@ public function getLocalOCMProvider(bool $fullDetails = true): IOCMProvider;
 	 * - if request is signed, but wrongly signed
 	 * - if request is not signed but instance is configured to only accept signed ocm request
 	 *
+	 * @param string|null $origin for RFC 9421, the signer origin from the caller
+	 *                            (the keyid is opaque)
+	 *
 	 * @return IIncomingSignedRequest|null null if remote does not (and never did) support signed request
 	 * @throws IncomingRequestException
 	 * @since 33.0.0
 	 */
-	public function getIncomingSignedRequest(): ?IIncomingSignedRequest;
+	public function getIncomingSignedRequest(?string $origin = null): ?IIncomingSignedRequest;
 
 	/**
 	 * Confirm that the host portion of $ocmAddress matches $signedOrigin
@@ -76,10 +79,20 @@ public function getIncomingSignedRequest(): ?IIncomingSignedRequest;
 	 * @param string $ocmAddress in `user@host` or `user@https://host` form
 	 *
 	 * @throws IncomingRequestException on mismatch or malformed address
-	 * @since 34.0.0
+	 * @since 35.0.0
 	 */
 	public function confirmRequestOrigin(?string $signedOrigin, string $ocmAddress): void;
 
+	/**
+	 * Extract the signer origin (host) from an OCM address (`user@host`).
+	 *
+	 * @param string $entry OCM address in `user@host` or `user@https://host` form
+	 * @return string the host (with port) of the OCM address
+	 * @throws IncomingRequestException on malformed address or unresolvable host
+	 * @since 35.0.0
+	 */
+	public function getHostFromOcmAddress(string $entry): string;
+
 	/**
 	 * Request a remote OCM endpoint.
 	 *
diff --git a/lib/public/OCM/IOCMProvider.php b/lib/public/OCM/IOCMProvider.php
index bcda666578438..0655e6ad2ad79 100644
--- a/lib/public/OCM/IOCMProvider.php
+++ b/lib/public/OCM/IOCMProvider.php
@@ -160,6 +160,27 @@ public function setCapabilities(array $capabilities): static;
 	 */
 	public function setInviteAcceptDialog(string $inviteAcceptDialog): static;
 
+	/**
+	 * get the URL of the JWK Set document (RFC 7517) containing the public
+	 * keys this OCM provider uses for HTTP Message Signatures (RFC 9421)
+	 *
+	 * @return string empty string if not advertised
+	 * @since 35.0.0
+	 */
+	public function getJwksUri(): string;
+
+	/**
+	 * set the URL of the JWK Set document (RFC 7517) containing the public
+	 * keys this OCM provider uses for HTTP Message Signatures (RFC 9421).
+	 * MUST use https when the `http-sig` capability is advertised.
+	 *
+	 * @param string $jwksUri
+	 *
+	 * @return $this
+	 * @since 35.0.0
+	 */
+	public function setJwksUri(string $jwksUri): static;
+
 	/**
 	 * get the token endpoint URL
 	 *
@@ -230,7 +251,8 @@ public function import(array $data): static;
 	 *         shareTypes: list<string>,
 	 *         protocols: array<string, string>
 	 *     }>,
-	 *     version: string
+	 *     version: string,
+	 *     jwksUri?: string
 	 * }
 	 * @since 28.0.0
 	 */
diff --git a/lib/public/Security/Signature/ISignatureManager.php b/lib/public/Security/Signature/ISignatureManager.php
index e4246d2f82089..ddc7be4778795 100644
--- a/lib/public/Security/Signature/ISignatureManager.php
+++ b/lib/public/Security/Signature/ISignatureManager.php
@@ -66,6 +66,8 @@ interface ISignatureManager {
 	 *
 	 * @param ISignatoryManager $signatoryManager used to get details about remote instance
 	 * @param string|null $body if NULL, body will be extracted from php://input
+	 * @param string|null $origin for RFC 9421, the signer origin from the caller
+	 *                            (the keyid is opaque)
 	 *
 	 * @return IIncomingSignedRequest
 	 * @throws IncomingRequestException if anything looks wrong with the incoming request
@@ -73,7 +75,11 @@ interface ISignatureManager {
 	 * @throws SignatureException if signature could not be confirmed
 	 * @since 33.0.0
 	 */
-	public function getIncomingSignedRequest(ISignatoryManager $signatoryManager, ?string $body = null): IIncomingSignedRequest;
+	public function getIncomingSignedRequest(
+		ISignatoryManager $signatoryManager,
+		?string $body = null,
+		?string $origin = null,
+	): IIncomingSignedRequest;
 
 	/**
 	 * Preparing signature (and headers) to sign an outgoing request.
diff --git a/openapi.json b/openapi.json
index 25ef87591e40b..48cfc9a7925b6 100644
--- a/openapi.json
+++ b/openapi.json
@@ -37,14 +37,14 @@
             "name": "core/open_metrics",
             "description": "OpenMetrics controller Gather and display metrics"
         },
-        {
-            "name": "cloud_federation_api/request_handler",
-            "description": "Open-Cloud-Mesh-API"
-        },
         {
             "name": "cloud_federation_api/token",
             "description": "Controller for the /token endpoint Exchanges long-lived refresh tokens for short-lived access tokens"
         },
+        {
+            "name": "cloud_federation_api/request_handler",
+            "description": "Open-Cloud-Mesh-API"
+        },
         {
             "name": "federatedfilesharing/mount_public_link",
             "description": "Class MountPublicLinkController convert public links to federated shares"
diff --git a/tests/lib/OCM/DiscoveryServiceTest.php b/tests/lib/OCM/DiscoveryServiceTest.php
index d218b2dec93bb..e1d41e565fb43 100644
--- a/tests/lib/OCM/DiscoveryServiceTest.php
+++ b/tests/lib/OCM/DiscoveryServiceTest.php
@@ -14,6 +14,7 @@
 use OCA\CloudFederationAPI\Controller\OCMRequestController;
 use OCP\EventDispatcher\IEventDispatcher;
 use OCP\IConfig;
+use OCP\IURLGenerator;
 use OCP\OCM\Events\LocalOCMDiscoveryEvent;
 use OCP\OCM\Events\OCMEndpointRequestEvent;
 use OCP\Server;
@@ -130,12 +131,22 @@ public function testLocalBaseCapability(): void {
 
 	public function testLocalCapabilitiesAdvertiseHttpSigByDefault(): void {
 		// `http-sig` is the OCM-spec flag signalling RFC 9421 support backed
-		// by /.well-known/jwks.json. Advertised whenever signing is not
-		// disabled outright.
+		// by the JWK Set published at the URL in `jwksUri`. Advertised
+		// whenever signing is not disabled outright.
 		$local = $this->discoveryService->getLocalOCMProvider();
 		$this->assertTrue($local->hasCapability('http-sig'));
 	}
 
+	public function testLocalDiscoveryAdvertisesJwksUri(): void {
+		// scheme follows the instance base URL
+		$local = $this->discoveryService->getLocalOCMProvider();
+		$jwksUri = $local->getJwksUri();
+		$baseUrl = Server::get(IURLGenerator::class)->getBaseUrl();
+		$expectedScheme = str_starts_with($baseUrl, 'http://') ? 'http://' : 'https://';
+		$this->assertStringStartsWith($expectedScheme, $jwksUri);
+		$this->assertStringContainsString('cloud_federation_api/api/v1/jwks', $jwksUri);
+	}
+
 	public function testLocalAddedCapability(): void {
 		$this->context->for('ocm-capability-app')->registerEventListener(LocalOCMDiscoveryEvent::class, LocalOCMDiscoveryTestEvent::class);
 		$this->context->delegateEventListenerRegistrations($this->dispatcher);
diff --git a/tests/lib/OCM/OCMJwksHandlerTest.php b/tests/lib/OCM/OCMJwksHandlerTest.php
deleted file mode 100644
index f7270298dee09..0000000000000
--- a/tests/lib/OCM/OCMJwksHandlerTest.php
+++ /dev/null
@@ -1,118 +0,0 @@
-<?php
-
-declare(strict_types=1);
-
-/**
- * SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
- * SPDX-License-Identifier: AGPL-3.0-or-later
- */
-
-namespace Test\OCM;
-
-use OC\OCM\OCMJwksHandler;
-use OC\OCM\OCMSignatoryManager;
-use OCP\AppFramework\Http\JSONResponse;
-use OCP\Http\WellKnown\GenericResponse;
-use OCP\Http\WellKnown\IRequestContext;
-use OCP\Http\WellKnown\IResponse;
-use OCP\Http\WellKnown\JrdResponse;
-use OCP\IAppConfig;
-use PHPUnit\Framework\MockObject\MockObject;
-use Psr\Log\LoggerInterface;
-use Test\TestCase;
-
-class OCMJwksHandlerTest extends TestCase {
-	private IAppConfig&MockObject $appConfig;
-	private OCMSignatoryManager&MockObject $signatoryManager;
-	private LoggerInterface&MockObject $logger;
-	private IRequestContext&MockObject $context;
-	private OCMJwksHandler $handler;
-
-	#[\Override]
-	protected function setUp(): void {
-		parent::setUp();
-
-		$this->appConfig = $this->createMock(IAppConfig::class);
-		$this->signatoryManager = $this->createMock(OCMSignatoryManager::class);
-		$this->logger = $this->createMock(LoggerInterface::class);
-		$this->context = $this->createMock(IRequestContext::class);
-
-		$this->handler = new OCMJwksHandler(
-			$this->appConfig,
-			$this->signatoryManager,
-			$this->logger,
-		);
-	}
-
-	public function testIgnoresUnrelatedService(): void {
-		$previous = new JrdResponse('foo');
-		$result = $this->handler->handle('webfinger', $this->context, $previous);
-		$this->assertSame($previous, $result);
-	}
-
-	public function testEmptyKeySetWhenSigningDisabled(): void {
-		$this->appConfig->method('getValueBool')
-			->with('core', OCMSignatoryManager::APPCONFIG_SIGN_DISABLED, false, true)
-			->willReturn(true);
-		$this->signatoryManager->expects($this->never())->method('getLocalJwks');
-
-		$body = $this->jsonBody($this->handler->handle('jwks.json', $this->context, null));
-		$this->assertSame(['keys' => []], $body);
-	}
-
-	public function testPublishesJwksWhenAvailable(): void {
-		$this->appConfig->method('getValueBool')->willReturn(false);
-		$jwk = [
-			'kty' => 'EC',
-			'crv' => 'P-256',
-			'kid' => 'https://example.org/ocm#ecdsa-p256-sha256',
-			'alg' => 'ES256',
-			'use' => 'sig',
-			'x' => 'AAAA',
-			'y' => 'BBBB',
-		];
-		$this->signatoryManager->method('getLocalJwks')->willReturn([$jwk]);
-
-		$body = $this->jsonBody($this->handler->handle('jwks.json', $this->context, null));
-		$this->assertSame(['keys' => [$jwk]], $body);
-	}
-
-	public function testPublishesAllSlotsAdvertisedDuringRotation(): void {
-		$this->appConfig->method('getValueBool')->willReturn(false);
-		$active = [
-			'kty' => 'EC', 'crv' => 'P-256', 'kid' => 'kid-1', 'alg' => 'ES256', 'use' => 'sig', 'x' => 'AAAA', 'y' => 'BBBB',
-		];
-		$pending = [
-			'kty' => 'EC', 'crv' => 'P-256', 'kid' => 'kid-2', 'alg' => 'ES256', 'use' => 'sig', 'x' => 'CCCC', 'y' => 'DDDD',
-		];
-		$this->signatoryManager->method('getLocalJwks')->willReturn([$active, $pending]);
-
-		$body = $this->jsonBody($this->handler->handle('jwks.json', $this->context, null));
-		$this->assertSame(['keys' => [$active, $pending]], $body);
-	}
-
-	public function testEmptyKeySetWhenSignatoryUnavailable(): void {
-		$this->appConfig->method('getValueBool')->willReturn(false);
-		$this->signatoryManager->method('getLocalJwks')->willReturn([]);
-
-		$body = $this->jsonBody($this->handler->handle('jwks.json', $this->context, null));
-		$this->assertSame(['keys' => []], $body);
-	}
-
-	public function testFailingJwkBuildIsLoggedAndYieldsEmptyKeySet(): void {
-		$this->appConfig->method('getValueBool')->willReturn(false);
-		$this->signatoryManager->method('getLocalJwks')
-			->willThrowException(new \RuntimeException('boom'));
-		$this->logger->expects($this->once())->method('warning');
-
-		$body = $this->jsonBody($this->handler->handle('jwks.json', $this->context, null));
-		$this->assertSame(['keys' => []], $body);
-	}
-
-	private function jsonBody(?IResponse $response): array {
-		$this->assertInstanceOf(GenericResponse::class, $response);
-		$http = $response->toHttpResponse();
-		$this->assertInstanceOf(JSONResponse::class, $http);
-		return $http->getData();
-	}
-}
diff --git a/tests/lib/OCM/OCMProviderTest.php b/tests/lib/OCM/OCMProviderTest.php
index bae2abef9a8b4..dce9cc1c2567f 100644
--- a/tests/lib/OCM/OCMProviderTest.php
+++ b/tests/lib/OCM/OCMProviderTest.php
@@ -69,4 +69,30 @@ public function testAddResourceTypeMergeOverwritesSameProtocol(): void {
 			$this->provider->getResourceTypes()[0]->getProtocols(),
 		);
 	}
+
+	public function testJwksUriImportedFromDiscoveryData(): void {
+		$this->provider->import([
+			'enabled' => true,
+			'apiVersion' => '1.1.0',
+			'endPoint' => 'https://cloud.example.org/ocm',
+			'capabilities' => ['http-sig'],
+			'jwksUri' => 'https://cloud.example.org/ocm/jwks',
+		]);
+
+		$this->assertSame('https://cloud.example.org/ocm/jwks', $this->provider->getJwksUri());
+	}
+
+	public function testJwksUriSerializedOnlyWhenSet(): void {
+		$this->provider->setEnabled(true)
+			->setApiVersion('1.1.0')
+			->setEndPoint('https://cloud.example.org/ocm');
+
+		$this->assertArrayNotHasKey('jwksUri', $this->provider->jsonSerialize());
+
+		$this->provider->setJwksUri('https://cloud.example.org/ocm/jwks');
+		$this->assertSame(
+			'https://cloud.example.org/ocm/jwks',
+			$this->provider->jsonSerialize()['jwksUri'],
+		);
+	}
 }
diff --git a/tests/lib/OCM/OCMSignatoryManagerJwksTest.php b/tests/lib/OCM/OCMSignatoryManagerJwksTest.php
index ee13ee352c194..3377c4f7784a2 100644
--- a/tests/lib/OCM/OCMSignatoryManagerJwksTest.php
+++ b/tests/lib/OCM/OCMSignatoryManagerJwksTest.php
@@ -10,6 +10,7 @@
 namespace Test\OCM;
 
 use OC\Memcache\ArrayCache;
+use OC\OCM\Model\OCMProvider;
 use OC\OCM\OCMSignatoryManager;
 use OC\Security\IdentityProof\Manager as IdentityProofManager;
 use OCP\Http\Client\IClient;
@@ -19,6 +20,8 @@
 use OCP\ICacheFactory;
 use OCP\IConfig;
 use OCP\IURLGenerator;
+use OCP\OCM\Exceptions\OCMProviderException;
+use OCP\OCM\IOCMDiscoveryService;
 use OCP\Security\Signature\ISignatureManager;
 use PHPUnit\Framework\MockObject\MockObject;
 use Psr\Log\LoggerInterface;
@@ -28,6 +31,10 @@ class OCMSignatoryManagerJwksTest extends TestCase {
 	/** RFC 7517 §A.1 test vector for an EC P-256 public key. */
 	private const TEST_X = 'f83OJ3D2xF1Bg8vub9tLe1gHMzV76e8Tus9uPHvRVEU';
 	private const TEST_Y = 'x_FEzRu9m36HLN_tue659LNpXW6pCyStikYjKIWI5a0';
+	/** RFC 8037 §A.2 test vector for an Ed25519 public key. */
+	private const TEST_OKP_X = '11qYAYKxCrfVS_7TyWQHOg7hcvPapiMlrwIaaPcHURo';
+
+	private const JWKS_URI = 'https://sender.example.org/ocm/jwks';
 
 	private IAppConfig&MockObject $appConfig;
 	private ISignatureManager&MockObject $signatureManager;
@@ -37,6 +44,7 @@ class OCMSignatoryManagerJwksTest extends TestCase {
 	private IConfig&MockObject $config;
 	private LoggerInterface&MockObject $logger;
 	private IClient&MockObject $client;
+	private IOCMDiscoveryService&MockObject $discoveryService;
 	private OCMSignatoryManager $signatoryManager;
 
 	#[\Override]
@@ -51,8 +59,10 @@ protected function setUp(): void {
 		$this->config = $this->createMock(IConfig::class);
 		$this->logger = $this->createMock(LoggerInterface::class);
 		$this->client = $this->createMock(IClient::class);
+		$this->discoveryService = $this->createMock(IOCMDiscoveryService::class);
 
 		$this->clientService->method('newClient')->willReturn($this->client);
+		$this->overwriteService(IOCMDiscoveryService::class, $this->discoveryService);
 
 		$cacheFactory = $this->createMock(ICacheFactory::class);
 		$cacheFactory->method('createDistributed')->willReturn(new ArrayCache(''));
@@ -69,7 +79,27 @@ protected function setUp(): void {
 		);
 	}
 
+	#[\Override]
+	protected function tearDown(): void {
+		$this->restoreService(IOCMDiscoveryService::class);
+		parent::tearDown();
+	}
+
+	/** Remote discovery response advertising http-sig and $jwksUri. */
+	private function primeDiscovery(
+		string $jwksUri = self::JWKS_URI,
+		array $capabilities = ['http-sig'],
+		string $endPoint = 'https://sender.example.org/ocm',
+	): void {
+		$provider = new OCMProvider();
+		$provider->setCapabilities($capabilities);
+		$provider->setJwksUri($jwksUri);
+		$provider->setEndPoint($endPoint);
+		$this->discoveryService->method('discover')->willReturn($provider);
+	}
+
 	public function testGetRemoteKeyFetchesAndMatchesByKid(): void {
+		$this->primeDiscovery();
 		$kid = 'sender.example.org#key1';
 		$jwks = [
 			'keys' => [
@@ -85,17 +115,20 @@ public function testGetRemoteKeyFetchesAndMatchesByKid(): void {
 	}
 
 	public function testGetRemoteKeyReturnsNullWhenKidMissing(): void {
+		$this->primeDiscovery();
 		$this->respondWith(['keys' => [$this->ecJwk('unrelated')]]);
 		$this->assertNull($this->signatoryManager->getRemoteKey('sender.example.org', 'other-kid'));
 	}
 
 	public function testGetRemoteKeyReturnsNullOnHttpError(): void {
+		$this->primeDiscovery();
 		$this->client->method('get')->willThrowException(new \RuntimeException('boom'));
 		$this->logger->expects($this->once())->method('warning');
 		$this->assertNull($this->signatoryManager->getRemoteKey('sender.example.org', 'kid'));
 	}
 
 	public function testGetRemoteKeyReturnsNullOnInvalidJson(): void {
+		$this->primeDiscovery();
 		$response = $this->createMock(IResponse::class);
 		$response->method('getBody')->willReturn('not json');
 		$this->client->method('get')->willReturn($response);
@@ -104,22 +137,25 @@ public function testGetRemoteKeyReturnsNullOnInvalidJson(): void {
 	}
 
 	public function testGetRemoteKeyReturnsNullWhenKeysMissing(): void {
+		$this->primeDiscovery();
 		$this->respondWith(['no-keys-here' => []]);
 		$this->assertNull($this->signatoryManager->getRemoteKey('sender.example.org', 'kid'));
 	}
 
 	public function testGetRemoteKeyReturnsNullOnUnparseableJwk(): void {
+		$this->primeDiscovery();
 		// JWK with kty=EC but no crv: parseKey rejects.
-		$this->respondWith(['keys' => [['kty' => 'EC', 'kid' => 'kid', 'x' => self::TEST_X, 'y' => self::TEST_Y]]]);
+		$this->respondWith(['keys' => [['kty' => 'EC', 'kid' => 'kid', 'alg' => 'ES256', 'x' => self::TEST_X, 'y' => self::TEST_Y]]]);
 		$this->logger->expects($this->once())->method('warning');
 		$this->assertNull($this->signatoryManager->getRemoteKey('sender.example.org', 'kid'));
 	}
 
-	public function testGetRemoteKeyUsesWellKnownPath(): void {
+	public function testGetRemoteKeyFetchesFromAdvertisedJwksUri(): void {
+		$this->primeDiscovery();
 		$this->client->expects($this->once())
 			->method('get')
 			->with(
-				$this->equalTo('https://sender.example.org/.well-known/jwks.json'),
+				$this->equalTo(self::JWKS_URI),
 				$this->isType('array'),
 			)
 			->willReturn($this->jsonResponse(['keys' => []]));
@@ -127,7 +163,94 @@ public function testGetRemoteKeyUsesWellKnownPath(): void {
 		$this->signatoryManager->getRemoteKey('sender.example.org', 'kid');
 	}
 
+	public function testGetRemoteKeyRejectsMissingJwksUriWhenHttpSigAdvertised(): void {
+		// a peer advertising http-sig without a jwksUri is non-conformant
+		$this->primeDiscovery(jwksUri: '');
+		$this->client->expects($this->never())->method('get');
+		$this->logger->expects($this->once())->method('warning');
+		$this->assertNull($this->signatoryManager->getRemoteKey('sender.example.org', 'kid'));
+	}
+
+	public function testGetRemoteKeyRejectsHttpJwksUriFromHttpsPeer(): void {
+		// downgrade guard: http jwksUri from an https peer
+		$this->primeDiscovery(jwksUri: 'http://sender.example.org/ocm/jwks');
+		$this->client->expects($this->never())->method('get');
+		$this->logger->expects($this->once())->method('warning');
+		$this->assertNull($this->signatoryManager->getRemoteKey('sender.example.org', 'kid'));
+	}
+
+	public function testGetRemoteKeyAcceptsHttpJwksUriFromHttpPeer(): void {
+		// the spec's http fallback for testing setups
+		$this->primeDiscovery(
+			jwksUri: 'http://sender.example.org/ocm/jwks',
+			endPoint: 'http://sender.example.org/ocm',
+		);
+		$kid = 'sender.example.org#key1';
+		$this->client->expects($this->once())
+			->method('get')
+			->with(
+				$this->equalTo('http://sender.example.org/ocm/jwks'),
+				$this->isType('array'),
+			)
+			->willReturn($this->jsonResponse(['keys' => [$this->ecJwk($kid)]]));
+
+		$this->assertNotNull($this->signatoryManager->getRemoteKey('sender.example.org', $kid));
+	}
+
+	public function testGetRemoteKeyReturnsNullWhenDiscoveryFails(): void {
+		$this->discoveryService->method('discover')
+			->willThrowException(new OCMProviderException('no discovery'));
+		$this->client->expects($this->never())->method('get');
+		$this->logger->expects($this->once())->method('warning');
+		$this->assertNull($this->signatoryManager->getRemoteKey('sender.example.org', 'kid'));
+	}
+
+	public function testGetRemoteKeyRejectsJwkWithoutAlg(): void {
+		$this->primeDiscovery();
+		$jwk = $this->ecJwk('kid');
+		unset($jwk['alg']);
+		$this->respondWith(['keys' => [$jwk]]);
+		$this->logger->expects($this->once())->method('warning');
+		$this->assertNull($this->signatoryManager->getRemoteKey('sender.example.org', 'kid'));
+	}
+
+	public function testGetRemoteKeyRejectsJwkWithSymmetricAlg(): void {
+		$this->primeDiscovery();
+		$jwk = $this->ecJwk('kid');
+		$jwk['alg'] = 'HS256';
+		$this->respondWith(['keys' => [$jwk]]);
+		$this->logger->expects($this->once())->method('warning');
+		$this->assertNull($this->signatoryManager->getRemoteKey('sender.example.org', 'kid'));
+	}
+
+	public function testGetRemoteKeyRejectsJwkAlgMismatchingKeyType(): void {
+		$this->primeDiscovery();
+		// EC P-256 key claiming an Ed25519 algorithm
+		$jwk = $this->ecJwk('kid');
+		$jwk['alg'] = 'Ed25519';
+		$this->respondWith(['keys' => [$jwk]]);
+		$this->logger->expects($this->once())->method('warning');
+		$this->assertNull($this->signatoryManager->getRemoteKey('sender.example.org', 'kid'));
+	}
+
+	public function testGetRemoteKeyAcceptsFullySpecifiedEd25519Alg(): void {
+		$this->primeDiscovery();
+		$this->respondWith(['keys' => [[
+			'kty' => 'OKP',
+			'crv' => 'Ed25519',
+			'kid' => 'kid',
+			'alg' => 'Ed25519',
+			'use' => 'sig',
+			'x' => self::TEST_OKP_X,
+		]]]);
+
+		$key = $this->signatoryManager->getRemoteKey('sender.example.org', 'kid');
+		$this->assertNotNull($key);
+		$this->assertSame('Ed25519', $key->getAlgorithm());
+	}
+
 	public function testGetRemoteKeyPassesSelfSignedFlagThrough(): void {
+		$this->primeDiscovery();
 		$this->config->method('getSystemValueBool')
 			->with('sharing.federation.allowSelfSignedCertificates')
 			->willReturn(true);
@@ -144,6 +267,7 @@ public function testGetRemoteKeyPassesSelfSignedFlagThrough(): void {
 	}
 
 	public function testJwksCachedAcrossCallsToTheSameOrigin(): void {
+		$this->primeDiscovery();
 		$kid = 'sender.example.org#key1';
 		$jwks = ['keys' => [$this->ecJwk($kid)]];
 		$this->client->expects($this->once())
@@ -155,6 +279,7 @@ public function testJwksCachedAcrossCallsToTheSameOrigin(): void {
 	}
 
 	public function testCacheMissOnNewKidTriggersRefetchOnce(): void {
+		$this->primeDiscovery();
 		$first = ['keys' => [$this->ecJwk('old')]];
 		$second = ['keys' => [$this->ecJwk('new')]];
 		$this->client->expects($this->exactly(2))
@@ -168,6 +293,51 @@ public function testCacheMissOnNewKidTriggersRefetchOnce(): void {
 		$this->assertNotNull($this->signatoryManager->getRemoteKey('sender.example.org', 'new'));
 	}
 
+	public function testGetRemoteKeyAcceptsHttpsJwksUriFromHttpPeer(): void {
+		// upgrade from an http-only peer is fine
+		$this->primeDiscovery(
+			endPoint: 'http://sender.example.org/ocm',
+		);
+		$kid = 'sender.example.org#key1';
+		$this->client->expects($this->once())
+			->method('get')
+			->with(
+				$this->equalTo(self::JWKS_URI),
+				$this->isType('array'),
+			)
+			->willReturn($this->jsonResponse(['keys' => [$this->ecJwk($kid)]]));
+
+		$this->assertNotNull($this->signatoryManager->getRemoteKey('sender.example.org', $kid));
+	}
+
+	public function testGetRemoteKeyAcceptsJwksUriOnDifferentHost(): void {
+		// the JWK Set may live on a different host than the peer
+		$this->primeDiscovery(
+			jwksUri: 'https://keys.example.net/ocm/jwks',
+			endPoint: 'http://sender.example.org/ocm',
+		);
+		$kid = 'sender.example.org#key1';
+		$this->client->expects($this->once())
+			->method('get')
+			->with(
+				$this->equalTo('https://keys.example.net/ocm/jwks'),
+				$this->isType('array'),
+			)
+			->willReturn($this->jsonResponse(['keys' => [$this->ecJwk($kid)]]));
+
+		$this->assertNotNull($this->signatoryManager->getRemoteKey('sender.example.org', $kid));
+	}
+
+	public function testGetLocalJwksUriPointsAtAppRoute(): void {
+		$this->urlGenerator->method('linkToRouteAbsolute')
+			->willReturn('https://sender.example.org/index.php/apps/cloud_federation_api/api/v1/jwks');
+
+		$this->assertSame(
+			'https://sender.example.org/index.php/apps/cloud_federation_api/api/v1/jwks',
+			$this->signatoryManager->getLocalJwksUri(),
+		);
+	}
+
 	private function respondWith(array $body): void {
 		$this->client->method('get')->willReturn($this->jsonResponse($body));
 	}
diff --git a/tests/lib/OCM/OCMSignatoryManagerRotationTest.php b/tests/lib/OCM/OCMSignatoryManagerRotationTest.php
index 3c1d7038ee78c..bc3a7f2530c54 100644
--- a/tests/lib/OCM/OCMSignatoryManagerRotationTest.php
+++ b/tests/lib/OCM/OCMSignatoryManagerRotationTest.php
@@ -19,7 +19,6 @@
 use OCP\ICacheFactory;
 use OCP\IConfig;
 use OCP\IURLGenerator;
-use OCP\Security\Signature\Exceptions\IdentityNotFoundException;
 use OCP\Security\Signature\ISignatureManager;
 use PHPUnit\Framework\MockObject\MockObject;
 use Psr\Log\LoggerInterface;
@@ -47,8 +46,9 @@ protected function setUp(): void {
 		$this->wireIdentityProofManager();
 
 		$signatureManager = $this->createMock(ISignatureManager::class);
-		$signatureManager->method('generateKeyIdFromConfig')
-			->willReturnCallback(static fn (string $suffix): string => 'https://alice.example/' . ltrim($suffix, '/'));
+		$urlGenerator = $this->createMock(IURLGenerator::class);
+		$urlGenerator->method('getAbsoluteURL')
+			->willReturnCallback(static fn (string $path): string => 'https://alice.example' . $path);
 
 		$cacheFactory = $this->createMock(ICacheFactory::class);
 		$cacheFactory->method('createDistributed')->willReturn(new ArrayCache(''));
@@ -56,7 +56,7 @@ protected function setUp(): void {
 		$this->signatoryManager = new OCMSignatoryManager(
 			$this->appConfig,
 			$signatureManager,
-			$this->createMock(IURLGenerator::class),
+			$urlGenerator,
 			$this->identityProofManager,
 			$this->stubClientService(),
 			$this->createMock(IConfig::class),
@@ -188,11 +188,10 @@ public function testSignerReturnsNullWhenIdentityCannotBeDerived(): void {
 		// identity at all; provisioning the first key should fail loudly so
 		// the admin gets a clear message instead of a corrupt half-state.
 		$signatureManager = $this->createMock(ISignatureManager::class);
-		$signatureManager->method('generateKeyIdFromConfig')
-			->willThrowException(new IdentityNotFoundException('no identity'));
 		$urlGenerator = $this->createMock(IURLGenerator::class);
-		$urlGenerator->method('linkToRouteAbsolute')
-			->willThrowException(new IdentityNotFoundException('no url either'));
+		// getAbsoluteURL() yields no host, so the kid's identity cannot be
+		// resolved; provisioning must fail loudly rather than corrupt state.
+		$urlGenerator->method('getAbsoluteURL')->willReturn('');
 
 		$cacheFactory = $this->createMock(ICacheFactory::class);
 		$cacheFactory->method('createDistributed')->willReturn(new ArrayCache(''));
diff --git a/tests/lib/Security/Signature/Model/Rfc9421RoundTripTest.php b/tests/lib/Security/Signature/Model/Rfc9421RoundTripTest.php
index e7d42460987f0..4639c1145b8d3 100644
--- a/tests/lib/Security/Signature/Model/Rfc9421RoundTripTest.php
+++ b/tests/lib/Security/Signature/Model/Rfc9421RoundTripTest.php
@@ -12,6 +12,8 @@
 use Firebase\JWT\JWK;
 use OC\Security\Signature\Model\Rfc9421IncomingSignedRequest;
 use OC\Security\Signature\Model\Rfc9421OutgoingSignedRequest;
+use OC\Security\Signature\Rfc9421\Algorithm;
+use OC\Security\Signature\Rfc9421\ContentDigest;
 use OCP\IRequest;
 use OCP\Security\Signature\Enum\DigestAlgorithm;
 use OCP\Security\Signature\Enum\SignatureAlgorithm;
@@ -39,6 +41,11 @@ public function testEcdsaP256RoundTripVerifies(): void {
 		$in->setKey($jwk);
 
 		$this->assertSame($out->getSignatureBaseString(), $in->getSignatureBaseString());
+		// the Date header is deliberately not covered by the signature
+		$this->assertSame(
+			['@method', '@target-uri', 'content-digest', 'content-length'],
+			$in->getCoveredComponents(),
+		);
 		$in->verify(); // throws on failure
 		$this->addToAssertionCount(1);
 	}
@@ -50,11 +57,18 @@ public function testEd25519VerifyAcceptedWhenSodiumLoaded(): void {
 
 		$body = '{"hello":"world"}';
 		$out = new Rfc9421OutgoingSignedRequest($body, $signatoryManager, 'receiver.example.org', 'POST', 'https://receiver.example.org/ocm/shares');
-		// Ed25519 sign() throws via Algorithm::sign; produce the signature directly.
-		$rawSig = sodium_crypto_sign_detached($out->getSignatureBaseString(), $signatory->getPrivateKey());
-		$out->setSignature(base64_encode($rawSig));
+		// Ed25519 sign() throws via Algorithm::sign; produce the signature directly
+		// over a manually reconstructed signature base.
 		$headers = $out->getHeaders();
-		$paramsLine = '("@method" "@target-uri" "content-digest" "content-length" "date");created=' . time() . ';keyid="' . $signatory->getKeyId() . '"';
+		$paramsLine = '("@method" "@target-uri" "content-digest" "content-length");created=' . time() . ';keyid="' . $signatory->getKeyId() . '";tag="ocm"';
+		$base = implode("\n", [
+			'"@method": POST',
+			'"@target-uri": https://receiver.example.org/ocm/shares',
+			'"content-digest": ' . $headers['Content-Digest'],
+			'"content-length": ' . $headers['Content-Length'],
+			'"@signature-params": ' . $paramsLine,
+		]);
+		$rawSig = sodium_crypto_sign_detached($base, $signatory->getPrivateKey());
 		$headers['Signature-Input'] = 'ocm=' . $paramsLine;
 		$headers['Signature'] = 'ocm=:' . base64_encode($rawSig) . ':';
 
@@ -98,7 +112,7 @@ public function testTamperedSignatureRejected(): void {
 		$in->verify();
 	}
 
-	public function testOutgoingUsesOcmLabel(): void {
+	public function testOutgoingCarriesOcmTag(): void {
 		[$signatory] = $this->ecdsaP256Material('https://sender.example.org/ocm#ecdsa-p256-sha256');
 		$signatoryManager = $this->makeSignatoryManager($signatory);
 
@@ -106,31 +120,72 @@ public function testOutgoingUsesOcmLabel(): void {
 		$out->sign();
 
 		$headers = $out->getHeaders();
+		// the label is cosmetic; the integrity-protected tag parameter is
+		// what marks the signature as the OCM one
 		$this->assertStringStartsWith('ocm=(', (string)$headers['Signature-Input']);
+		$this->assertStringContainsString(';tag="ocm"', (string)$headers['Signature-Input']);
 		$this->assertStringStartsWith('ocm=:', (string)$headers['Signature']);
 	}
 
-	public function testRequestWithoutOcmLabelRejected(): void {
-		[$signatory] = $this->ecdsaP256Material('https://sender.example.org/ocm#ecdsa-p256-sha256');
+	public function testArbitraryLabelWithOcmTagVerifies(): void {
+		[$signatory, $jwk] = $this->ecdsaP256Material('https://sender.example.org/ocm#ecdsa-p256-sha256');
 		$signatoryManager = $this->makeSignatoryManager($signatory);
 
 		$out = new Rfc9421OutgoingSignedRequest('msg', $signatoryManager, 'receiver.example.org', 'POST', 'https://receiver.example.org/ocm/shares');
 		$out->sign();
 
-		// Rename the OCM label to something else; verifier MUST reject.
+		// Rename the dictionary label; the verifier MUST select by the
+		// tag="ocm" parameter and disregard labels.
 		$headers = $out->getHeaders();
 		$headers['Signature-Input'] = preg_replace('/^ocm=/', 'sig1=', (string)$headers['Signature-Input']);
 		$headers['Signature'] = preg_replace('/^ocm=/', 'sig1=', (string)$headers['Signature']);
 
+		$req = $this->mockRequest($headers, 'POST', '/ocm/shares', 'receiver.example.org');
+		$in = new Rfc9421IncomingSignedRequest('msg', $req);
+		$in->setKey($jwk);
+		$in->verify();
+		$this->addToAssertionCount(1);
+	}
+
+	public function testRequestWithoutOcmTagTreatedAsUnsigned(): void {
+		[$signatory] = $this->ecdsaP256Material('https://sender.example.org/ocm#ecdsa-p256-sha256');
+		$signatoryManager = $this->makeSignatoryManager($signatory);
+
+		$out = new Rfc9421OutgoingSignedRequest('msg', $signatoryManager, 'receiver.example.org', 'POST', 'https://receiver.example.org/ocm/shares');
+		$out->sign();
+
+		// Strip the tag parameter; without tag="ocm" the request carries no
+		// OCM signature and is handled as unsigned.
+		$headers = $out->getHeaders();
+		$headers['Signature-Input'] = str_replace(';tag="ocm"', '', (string)$headers['Signature-Input']);
+
 		$req = $this->mockRequest($headers, 'POST', '/ocm/shares', 'receiver.example.org');
 		$this->expectException(SignatureNotFoundException::class);
 		new Rfc9421IncomingSignedRequest('msg', $req);
 	}
 
+	public function testTwoSignaturesCarryingOcmTagRejected(): void {
+		[$signatory] = $this->ecdsaP256Material('https://sender.example.org/ocm#ecdsa-p256-sha256');
+		$signatoryManager = $this->makeSignatoryManager($signatory);
+
+		$out = new Rfc9421OutgoingSignedRequest('msg', $signatoryManager, 'receiver.example.org', 'POST', 'https://receiver.example.org/ocm/shares');
+		$out->sign();
+
+		// A second, differently-labeled signature also carrying tag="ocm":
+		// the entire message MUST be rejected.
+		$headers = $out->getHeaders();
+		$headers['Signature-Input'] = (string)$headers['Signature-Input'] . ', ' . preg_replace('/^ocm=/', 'sig2=', (string)$headers['Signature-Input']);
+		$headers['Signature'] = (string)$headers['Signature'] . ', ' . preg_replace('/^ocm=/', 'sig2=', (string)$headers['Signature']);
+
+		$req = $this->mockRequest($headers, 'POST', '/ocm/shares', 'receiver.example.org');
+		$this->expectException(IncomingRequestException::class);
+		new Rfc9421IncomingSignedRequest('msg', $req);
+	}
+
 	public function testDuplicateOcmLabelRejected(): void {
-		// RFC 8941 §4.2 last-wins on duplicate dictionary keys, but OCM
-		// mandates that duplicate `ocm` entries cause the request to be
-		// rejected outright. The model layer enforces that.
+		// RFC 8941 §4.2 last-wins on duplicate dictionary keys, which would
+		// silently hide one of two identically-labeled OCM signatures; that
+		// ambiguity on the selected entry causes outright rejection.
 		[$signatory] = $this->ecdsaP256Material('https://sender.example.org/ocm#ecdsa-p256-sha256');
 		$signatoryManager = $this->makeSignatoryManager($signatory);
 
@@ -223,6 +278,44 @@ public function testMissingCreatedRejected(): void {
 		new Rfc9421IncomingSignedRequest($body, $req);
 	}
 
+	public function testMissingKeyidRejected(): void {
+		[$signatory] = $this->ecdsaP256Material('https://sender.example.org/ocm#ecdsa-p256-sha256');
+		$signatoryManager = $this->makeSignatoryManager($signatory);
+
+		$body = 'msg';
+		$out = new Rfc9421OutgoingSignedRequest($body, $signatoryManager, 'receiver.example.org', 'POST', 'https://receiver.example.org/ocm/shares');
+		$out->sign();
+
+		// Strip the `;keyid="..."` parameter; verifiers MUST reject
+		// signatures without it.
+		$headers = $out->getHeaders();
+		$headers['Signature-Input'] = preg_replace('/;keyid="[^"]*"/', '', (string)$headers['Signature-Input']);
+
+		$req = $this->mockRequest($headers, 'POST', '/ocm/shares', 'receiver.example.org');
+		$this->expectException(IncomingRequestException::class);
+		new Rfc9421IncomingSignedRequest($body, $req);
+	}
+
+	public function testExtraCoveredDateStillVerifies(): void {
+		// covering more than the mandatory components (here: `date`) is
+		// allowed; only the four baseline components are required
+		[$signatory, $jwk] = $this->ecdsaP256Material('https://sender.example.org/ocm#ecdsa-p256-sha256');
+		$signatoryManager = $this->makeSignatoryManagerWithComponents(
+			$signatory,
+			['@method', '@target-uri', 'content-digest', 'content-length', 'date'],
+		);
+
+		$body = 'msg';
+		$out = new Rfc9421OutgoingSignedRequest($body, $signatoryManager, 'receiver.example.org', 'POST', 'https://receiver.example.org/ocm/shares');
+		$out->sign();
+
+		$req = $this->mockRequestFromOutgoing($out, 'POST', '/ocm/shares', 'receiver.example.org');
+		$in = new Rfc9421IncomingSignedRequest($body, $req);
+		$in->setKey($jwk);
+		$in->verify();
+		$this->addToAssertionCount(1);
+	}
+
 	public function testSignatureNotCoveringRequiredComponentsRejected(): void {
 		// A peer that signs only `@method` and `@target-uri`: the body and
 		// freshness window aren't bound. Even with a valid signature we
@@ -242,6 +335,39 @@ public function testSignatureNotCoveringRequiredComponentsRejected(): void {
 		new Rfc9421IncomingSignedRequest($body, $req);
 	}
 
+	public function testKeyIdIsOpaqueAndOriginIsExternal(): void {
+		// keyid is opaque; the origin is supplied by the caller via setOrigin().
+		$kid = 'sender.example.org#key1';
+		[$privatePem, $jwk] = $this->ecdsaP256Jwk($kid);
+
+		$body = 'msg';
+		$digest = ContentDigest::compute($body, ContentDigest::ALGO_SHA256);
+		$paramsLine = '("@method" "@target-uri" "content-digest" "content-length");created=' . time() . ';keyid="' . $kid . '";tag="ocm"';
+		$base = implode("\n", [
+			'"@method": POST',
+			'"@target-uri": https://receiver.example.org/ocm/shares',
+			'"content-digest": ' . $digest,
+			'"content-length": ' . strlen($body),
+			'"@signature-params": ' . $paramsLine,
+		]);
+		$rawSig = Algorithm::sign($base, $privatePem, 'ecdsa-p256-sha256');
+		$headers = [
+			'Content-Digest' => $digest,
+			'Content-Length' => (string)strlen($body),
+			'Signature-Input' => 'sig1=' . $paramsLine,
+			'Signature' => 'sig1=:' . base64_encode($rawSig) . ':',
+		];
+
+		$req = $this->mockRequest($headers, 'POST', '/ocm/shares', 'receiver.example.org');
+		$in = new Rfc9421IncomingSignedRequest($body, $req);
+		// The keyid is not parsed; the origin comes from the caller.
+		$in->setOrigin('sender.example.org');
+		$this->assertSame('sender.example.org', $in->getOrigin());
+		$in->setKey($jwk);
+		$in->verify();
+		$this->addToAssertionCount(1);
+	}
+
 	private function skipUnlessSodium(): void {
 		if (!extension_loaded('sodium')) {
 			$this->markTestSkipped('ext-sodium is not loaded');
@@ -323,9 +449,29 @@ private function ecdsaP256Material(string $kid): array {
 		$signatory->setPublicKey($publicPem);
 		$signatory->setPrivateKey($privatePem);
 
+		$key = self::jwkFromEcDetails($details, $kid);
+		return [$signatory, $key];
+	}
+
+	/**
+	 * Key material for a peer whose kid is not a URL; Nextcloud's Signatory
+	 * model cannot represent those.
+	 *
+	 * @return array{0: string, 1: \Firebase\JWT\Key} [private key PEM, verification key]
+	 */
+	private function ecdsaP256Jwk(string $kid): array {
+		$pkey = openssl_pkey_new(['private_key_type' => OPENSSL_KEYTYPE_EC, 'curve_name' => 'prime256v1']);
+		$privatePem = '';
+		openssl_pkey_export($pkey, $privatePem);
+		$details = openssl_pkey_get_details($pkey);
+
+		return [$privatePem, self::jwkFromEcDetails($details, $kid)];
+	}
+
+	private static function jwkFromEcDetails(array $details, string $kid): \Firebase\JWT\Key {
 		$x = str_pad($details['ec']['x'], 32, "\x00", STR_PAD_LEFT);
 		$y = str_pad($details['ec']['y'], 32, "\x00", STR_PAD_LEFT);
-		$key = JWK::parseKey([
+		return JWK::parseKey([
 			'kty' => 'EC',
 			'crv' => 'P-256',
 			'kid' => $kid,
@@ -333,7 +479,6 @@ private function ecdsaP256Material(string $kid): array {
 			'x' => self::b64url($x),
 			'y' => self::b64url($y),
 		], 'ES256');
-		return [$signatory, $key];
 	}
 
 	/**
diff --git a/tests/lib/Security/Signature/Rfc9421/AlgorithmTest.php b/tests/lib/Security/Signature/Rfc9421/AlgorithmTest.php
index abcf200e76048..50610285c3b99 100644
--- a/tests/lib/Security/Signature/Rfc9421/AlgorithmTest.php
+++ b/tests/lib/Security/Signature/Rfc9421/AlgorithmTest.php
@@ -27,6 +27,8 @@ public function testNormalizeNativeIsPassThrough(): void {
 
 	public function testNormalizeJoseAliases(): void {
 		$this->assertSame('ed25519', Algorithm::normalize('EdDSA'));
+		// fully-specified RFC 9864 name, recommended by the OCM spec
+		$this->assertSame('ed25519', Algorithm::normalize('Ed25519'));
 		$this->assertSame('ecdsa-p256-sha256', Algorithm::normalize('ES256'));
 		$this->assertSame('ecdsa-p384-sha384', Algorithm::normalize('ES384'));
 		$this->assertSame('rsa-v1_5-sha256', Algorithm::normalize('RS256'));
@@ -117,7 +119,9 @@ public function testAlgHintConflictsWithJwkAlgRejected(): void {
 	public function testParseKeyRejectsContradictoryAlg(): void {
 		$this->markTestSkipped(
 			'firebase/php-jwt JWK::parseKey does not validate kty/crv/alg coherence; '
-			. 'the alg mismatch is caught at verify() time instead — see testVerifyEd25519KeyAgainstES256Alg.'
+			. 'OCMSignatoryManager::findKid() rejects such keys before parsing '
+			. '(see OCMSignatoryManagerJwksTest::testGetRemoteKeyRejectsJwkAlgMismatchingKeyType) '
+			. 'and a remaining mismatch is caught at verify() time.'
 		);
 	}
 
diff --git a/tests/lib/Security/Signature/SignatureManagerDispatchTest.php b/tests/lib/Security/Signature/SignatureManagerDispatchTest.php
index 698ea59d6188e..cc079272ccda4 100644
--- a/tests/lib/Security/Signature/SignatureManagerDispatchTest.php
+++ b/tests/lib/Security/Signature/SignatureManagerDispatchTest.php
@@ -100,7 +100,8 @@ public function testInboundDispatchesToRfc9421WhenSignatureInputPresent(): void
 
 		$resolver = $this->makeKeyResolver($signatoryManager, $jwk, 'https://sender.example.org/ocm#ecdsa-p256-sha256');
 
-		$signed = $this->signatureManager->getIncomingSignedRequest($resolver, $body);
+		// RFC 9421 verification needs the sender origin from the caller.
+		$signed = $this->signatureManager->getIncomingSignedRequest($resolver, $body, 'sender.example.org');
 		$this->assertInstanceOf(Rfc9421IncomingSignedRequest::class, $signed);
 	}
 
@@ -123,6 +124,29 @@ public function testInboundRejectsRfc9421WhenSignatoryManagerCannotResolve(): vo
 		$this->signatureManager->getIncomingSignedRequest($signatoryManager, $body);
 	}
 
+	public function testInboundRejectsRfc9421WhenNoKeyResolvedForKeyid(): void {
+		[$signatoryManager, $jwk] = $this->ecdsaP256SignatoryManager(rfc9421Format: true);
+
+		$body = '{"hello":"world"}';
+		$out = new Rfc9421OutgoingSignedRequest(
+			$body,
+			$signatoryManager,
+			'receiver.example.org',
+			'POST',
+			'https://receiver.example.org/ocm/shares',
+		);
+		$out->sign();
+		$this->primeRequest($out->getHeaders(), 'POST', '/ocm/shares', 'receiver.example.org');
+
+		// resolver knows a different kid only: a present signature whose key
+		// cannot be resolved is a verification failure, not an unsigned
+		// request
+		$resolver = $this->makeKeyResolver($signatoryManager, $jwk, 'https://other.example.org/ocm#nomatch');
+
+		$this->expectException(IncomingRequestException::class);
+		$this->signatureManager->getIncomingSignedRequest($resolver, $body, 'sender.example.org');
+	}
+
 	private function rsaSignatoryManager(): ISignatoryManager {
 		$key = openssl_pkey_new(['private_key_type' => OPENSSL_KEYTYPE_RSA, 'private_key_bits' => 2048]);
 		$priv = '';