diff --git a/apps/payments/api/src/app/app.module.ts b/apps/payments/api/src/app/app.module.ts
index 8f7ff1a477f..902ae0df13e 100644
--- a/apps/payments/api/src/app/app.module.ts
+++ b/apps/payments/api/src/app/app.module.ts
@@ -8,6 +8,7 @@ import {
   BillingAndSubscriptionsService,
 } from '@fxa/payments/api-server';
 import { AuthModule } from '@fxa/payments/auth';
+import { MeteringAuthGuard, MeteringConfig } from '@fxa/entitlements/metering';
 import {
   CmsWebhooksController,
   CmsWebhookService,
@@ -123,6 +124,8 @@ import { PaymentsMetricsAggregatorService } from '@fxa/payments/metrics-aggregat
     NimbusManagerConfig,
     NimbusClient,
     NimbusClientConfig,
+    MeteringConfig,
+    MeteringAuthGuard,
   ],
 })
 export class AppModule {}
diff --git a/libs/entitlements/metering/src/index.ts b/libs/entitlements/metering/src/index.ts
index 6b87f8950bb..103cf344a12 100644
--- a/libs/entitlements/metering/src/index.ts
+++ b/libs/entitlements/metering/src/index.ts
@@ -3,3 +3,5 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 export * from './lib/metering.config';
+export * from './lib/metering-auth.guard';
+export * from './lib/utils/extractBearerToken';
diff --git a/libs/entitlements/metering/src/lib/metering-auth.guard.spec.ts b/libs/entitlements/metering/src/lib/metering-auth.guard.spec.ts
new file mode 100644
index 00000000000..702e4ba6921
--- /dev/null
+++ b/libs/entitlements/metering/src/lib/metering-auth.guard.spec.ts
@@ -0,0 +1,149 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+import { UnauthorizedException } from '@nestjs/common';
+import { Test } from '@nestjs/testing';
+
+import {
+  AuthenticatedMeteringClient,
+  MeteringAuthGuard,
+  meteringClientFromRequest,
+} from './metering-auth.guard';
+import { MeteringConfig } from './metering.config';
+
+const REQUEST_CLIENT_KEY = '__meteringClient';
+
+function buildRequest(authorization?: string): {
+  headers: { authorization?: string };
+  [REQUEST_CLIENT_KEY]?: AuthenticatedMeteringClient;
+} {
+  return { headers: authorization ? { authorization } : {} };
+}
+
+async function buildGuard(
+  clients: Record<string, string>
+): Promise<MeteringAuthGuard> {
+  const moduleRef = await Test.createTestingModule({
+    providers: [
+      MeteringAuthGuard,
+      {
+        provide: MeteringConfig,
+        useValue: { openmeterBaseUrl: 'http://example.com', clients },
+      },
+    ],
+  }).compile();
+  return moduleRef.get(MeteringAuthGuard);
+}
+
+describe('MeteringAuthGuard', () => {
+  const RP_ID = 'vpn';
+  const RP_SECRET = 'super-secret-token-with-enough-entropy-aaaaaaaa';
+
+  describe('construction', () => {
+    it('throws if two clients share the same secret', async () => {
+      await expect(
+        buildGuard({ vpn: RP_SECRET, relay: RP_SECRET })
+      ).rejects.toThrow(/share the same secret/);
+    });
+
+    it('throws if a client has an empty secret', async () => {
+      await expect(buildGuard({ [RP_ID]: '   ' })).rejects.toThrow(
+        /empty secret/
+      );
+    });
+
+    it('detects duplicate secrets that differ only by surrounding whitespace', async () => {
+      await expect(
+        buildGuard({ vpn: RP_SECRET, relay: `  ${RP_SECRET}  ` })
+      ).rejects.toThrow(/share the same secret/);
+    });
+  });
+
+  describe('authorize', () => {
+    it('rejects requests without an authorization header', async () => {
+      const meteringAuthGuard = await buildGuard({ [RP_ID]: RP_SECRET });
+      expect(() => meteringAuthGuard.authorize(buildRequest())).toThrow(
+        UnauthorizedException
+      );
+    });
+
+    it('rejects requests with non-bearer auth headers', async () => {
+      const meteringAuthGuard = await buildGuard({ [RP_ID]: RP_SECRET });
+      expect(() =>
+        meteringAuthGuard.authorize(buildRequest('Basic abc'))
+      ).toThrow(UnauthorizedException);
+    });
+
+    it('rejects unknown bearer tokens', async () => {
+      const meteringAuthGuard = await buildGuard({ [RP_ID]: RP_SECRET });
+      expect(() =>
+        meteringAuthGuard.authorize(buildRequest('Bearer wrong-token'))
+      ).toThrow(UnauthorizedException);
+    });
+
+    it('rejects when no clients are configured', async () => {
+      const meteringAuthGuard = await buildGuard({});
+      expect(() =>
+        meteringAuthGuard.authorize(buildRequest(`Bearer ${RP_SECRET}`))
+      ).toThrow(UnauthorizedException);
+    });
+
+    it('attaches the matched clientId to the request on success', async () => {
+      const meteringAuthGuard = await buildGuard({ [RP_ID]: RP_SECRET });
+      const request = buildRequest(`Bearer ${RP_SECRET}`);
+
+      const result = meteringAuthGuard.authorize(request);
+
+      expect(result).toBe(true);
+      expect(request[REQUEST_CLIENT_KEY]).toEqual({ clientId: RP_ID });
+    });
+
+    it('matches a config secret padded with surrounding whitespace', async () => {
+      const meteringAuthGuard = await buildGuard({
+        [RP_ID]: `  ${RP_SECRET}  `,
+      });
+      const request = buildRequest(`Bearer ${RP_SECRET}`);
+
+      meteringAuthGuard.authorize(request);
+
+      expect(request[REQUEST_CLIENT_KEY]).toEqual({ clientId: RP_ID });
+    });
+
+    it('matches case-insensitively on the Bearer prefix', async () => {
+      const meteringAuthGuard = await buildGuard({ [RP_ID]: RP_SECRET });
+      const request = buildRequest(`bearer ${RP_SECRET}`);
+
+      meteringAuthGuard.authorize(request);
+
+      expect(request[REQUEST_CLIENT_KEY]).toEqual({ clientId: RP_ID });
+    });
+
+    it('overwrites any client already present on the request', async () => {
+      const meteringAuthGuard = await buildGuard({ [RP_ID]: RP_SECRET });
+      const request = {
+        ...buildRequest(`Bearer ${RP_SECRET}`),
+        [REQUEST_CLIENT_KEY]: { clientId: 'attacker' },
+      };
+
+      meteringAuthGuard.authorize(request);
+
+      expect(request[REQUEST_CLIENT_KEY]).toEqual({ clientId: RP_ID });
+    });
+  });
+
+  describe('meteringClientFromRequest', () => {
+    it('returns the authenticated client attached to the request', () => {
+      const client = { clientId: RP_ID };
+      expect(
+        meteringClientFromRequest({ [REQUEST_CLIENT_KEY]: client })
+      ).toEqual(client);
+    });
+
+    it('throws when no client is attached to the request', () => {
+      expect(() => meteringClientFromRequest({})).toThrow(
+        UnauthorizedException
+      );
+    });
+  });
+});
diff --git a/libs/entitlements/metering/src/lib/metering-auth.guard.ts b/libs/entitlements/metering/src/lib/metering-auth.guard.ts
new file mode 100644
index 00000000000..ef773dc6e55
--- /dev/null
+++ b/libs/entitlements/metering/src/lib/metering-auth.guard.ts
@@ -0,0 +1,95 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+import {
+  CanActivate,
+  ExecutionContext,
+  Injectable,
+  UnauthorizedException,
+  createParamDecorator,
+} from '@nestjs/common';
+import type { Request } from 'express';
+
+import { MeteringConfig } from './metering.config';
+import { extractBearerToken } from './utils/extractBearerToken';
+
+export interface AuthenticatedMeteringClient {
+  clientId: string;
+}
+
+const REQUEST_CLIENT_KEY = '__meteringClient';
+
+interface RequestWithClient extends Request {
+  [REQUEST_CLIENT_KEY]?: AuthenticatedMeteringClient;
+}
+
+/**
+ * Validates `Authorization: Bearer <token>` against
+ * `MeteringConfig.clients` `{ clientId: secret }`
+ */
+@Injectable()
+export class MeteringAuthGuard implements CanActivate {
+  private readonly clientIdByToken: Map<string, string>;
+
+  constructor(meteringConfig: MeteringConfig) {
+    this.clientIdByToken = new Map();
+    for (const [clientId, secret] of Object.entries(
+      meteringConfig.clients ?? {}
+    )) {
+      const normalizedSecret = typeof secret === 'string' ? secret.trim() : '';
+      if (normalizedSecret.length === 0) {
+        throw new Error(
+          `MeteringConfig.clients[${clientId}] has an empty secret`
+        );
+      }
+      const existing = this.clientIdByToken.get(normalizedSecret);
+      if (existing !== undefined) {
+        throw new Error(
+          `MeteringConfig.clients[${clientId}] and clients[${existing}] share the same secret`
+        );
+      }
+      this.clientIdByToken.set(normalizedSecret, clientId);
+    }
+  }
+
+  async canActivate(context: ExecutionContext): Promise<boolean> {
+    const request = context.switchToHttp().getRequest<RequestWithClient>();
+    return this.authorize(request);
+  }
+
+  authorize(request: {
+    headers: Request['headers'];
+    [REQUEST_CLIENT_KEY]?: AuthenticatedMeteringClient;
+  }): boolean {
+    const token = extractBearerToken(request.headers['authorization']);
+    if (!token) {
+      throw new UnauthorizedException();
+    }
+
+    const clientId = this.clientIdByToken.get(token);
+    if (!clientId) {
+      throw new UnauthorizedException();
+    }
+
+    request[REQUEST_CLIENT_KEY] = { clientId };
+    return true;
+  }
+}
+
+export function meteringClientFromRequest(request: {
+  [REQUEST_CLIENT_KEY]?: AuthenticatedMeteringClient;
+}): AuthenticatedMeteringClient {
+  const authenticatedMeteringClient = request[REQUEST_CLIENT_KEY];
+  if (!authenticatedMeteringClient) {
+    throw new UnauthorizedException();
+  }
+  return authenticatedMeteringClient;
+}
+
+export const CurrentMeteringClient = createParamDecorator(
+  (_data: unknown, context: ExecutionContext): AuthenticatedMeteringClient =>
+    meteringClientFromRequest(
+      context.switchToHttp().getRequest<RequestWithClient>()
+    )
+);
diff --git a/libs/entitlements/metering/src/lib/utils/extractBearerToken.spec.ts b/libs/entitlements/metering/src/lib/utils/extractBearerToken.spec.ts
new file mode 100644
index 00000000000..d9a7db6fe31
--- /dev/null
+++ b/libs/entitlements/metering/src/lib/utils/extractBearerToken.spec.ts
@@ -0,0 +1,41 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+import { extractBearerToken } from './extractBearerToken';
+
+describe('extractBearerToken', () => {
+  it('returns the token after a Bearer prefix', () => {
+    expect(extractBearerToken('Bearer abc123')).toBe('abc123');
+  });
+
+  it('matches case-insensitively', () => {
+    expect(extractBearerToken('bearer abc123')).toBe('abc123');
+    expect(extractBearerToken('BEARER abc123')).toBe('abc123');
+  });
+
+  it('strips surrounding whitespace from the header and the token', () => {
+    expect(extractBearerToken('  Bearer   abc123  ')).toBe('abc123');
+  });
+
+  it('uses the first value when the header is an array', () => {
+    expect(extractBearerToken(['Bearer xyz', 'Bearer other'])).toBe('xyz');
+  });
+
+  it('returns null when the header is missing', () => {
+    expect(extractBearerToken(undefined)).toBeNull();
+  });
+
+  it('returns null when the header does not start with Bearer', () => {
+    expect(extractBearerToken('Token abc')).toBeNull();
+    expect(extractBearerToken('abc')).toBeNull();
+  });
+
+  it('returns null when the token portion is empty', () => {
+    expect(extractBearerToken('Bearer ')).toBeNull();
+  });
+
+  it('returns null when the token contains internal whitespace', () => {
+    expect(extractBearerToken('Bearer abc def')).toBeNull();
+  });
+});
diff --git a/libs/entitlements/metering/src/lib/utils/extractBearerToken.ts b/libs/entitlements/metering/src/lib/utils/extractBearerToken.ts
new file mode 100644
index 00000000000..e6594aa3cf2
--- /dev/null
+++ b/libs/entitlements/metering/src/lib/utils/extractBearerToken.ts
@@ -0,0 +1,14 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+export function extractBearerToken(
+  header: string | string[] | undefined
+): string | null {
+  const value = Array.isArray(header) ? header[0] : header;
+  if (typeof value !== 'string') {
+    return null;
+  }
+  const match = /^Bearer\s+(\S+)$/i.exec(value.trim());
+  return match ? match[1] : null;
+}