feat: define credential validity contracts#787
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July 22, 2026 09:02
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Summary
SigningCredential::is_valid()currently mixes cache freshness with exact operation usability. This can make a successful refresh return the same still-live token inside its proactive refresh window, only for the request signer to reject it. Core also interpretsexpires_inas a universal credential lifetime even though service authentication paths have different requirements.This change defines
is_valid()as cache freshness andis_valid_at()as exact timestamp usability. It addsSignRequest::required_valid_until()so each service owns its signing clock, interpretation ofexpires_in, and explicit operation headroom. The new hook has a default implementation, so normal downstream implementations remain source-compatible while adopting the new documented semantics.Cached credentials must be both fresh and usable for the operation. Refreshed credentials only need to satisfy the exact operation deadline and are cached even when they remain inside the refresh window. Provider errors and
Noneremain visible to the caller;Signerperforms no internal retry or stale-cache fallback. Individual provider-chain fallback policies are unchanged.The built-in credential types and signers now implement these contracts for AWS, Azure, Google, Aliyun, Huawei, Oracle, Tencent, and Volcengine, including direct-call validation and request failure atomicity.
Closes #786.