## What changed
Add a `GithubOidc` implementation of `SubjectTokenSource` that requests a fresh token using a bearer credential read from stdin. Validate HTTPS request URLs and replace the audience query parameter while preserving other parameters. CLI integration is not included.
Add a token HTTP client that disables redirects and request logging, applies timeouts, and bounds response bodies. Keep token response buffers in zeroizing storage and exclude credentials, request URLs, and response bodies from errors.
Generalize the locked stdin credential reader for bounded OIDC bearer tokens while preserving API key validation.
## Testing
Add tests for fresh token acquisition, short reads, credential size limits, injection rejection, redirect refusal, and credential-safe errors and logs. Extend API key tests to retain the stricter character restrictions.
GitOrigin-RevId: fd7767178f475b8161734f29d29108c795839185
## What changed
Introduce a shared `Auth` abstraction that supplies sensitive authorization headers and the client's redirect policy. Preserve the existing static API key allocation and default redirect behavior, and return an empty `502` response if header acquisition fails.
Unify the stdin authentication entry point around platform-specific `read_from_stdin` helpers.
## Testing
Add a test verifying that both compact and pretty `Debug` output redact API keys.
GitOrigin-RevId: 6a924534f00c1b209b24e8b0af117091cfa3ec07
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