Retry failed JWT key refreshes with exponential backoff

[Copilot]

JWT key refresh previously waited for the configured periodic interval after failures, which defaults to 30 minutes. Existing outage coverage checked failure metrics but not subsequent recovery.

Changes

• Retry scheduling

  • Track retries independently per issuer.
  • Retry after min(5 seconds, key_refresh_interval).
  • Exponentially back off to the configured interval.
  • Coalesce pending retries and discard stale tasks safely.
  • Cancel retry state after success, issuer removal, or role change.

• Outage recovery coverage

  • Extend the unavailable-endpoint test to start the issuer after an initial connection failure.
  • Verify keys refresh before the deliberately long periodic interval expires.

• Documentation

  • Document retry behavior in the JWT operator guide and changelog.

• Fixes Make JWT refresh more robust #3869

[Copilot]

Pull request overview

This PR improves JWT/JWK auto-refresh robustness in CCF by adding per-issuer retry scheduling with exponential backoff, so transient OpenID/JWKS endpoint failures recover quickly rather than waiting for the (often long) periodic refresh interval.

Changes:

• Add per-issuer retry state and delayed-task scheduling to retry failed refreshes quickly, then exponentially back off up to the configured refresh interval.
• Extend the connection-failure e2e test to verify recovery once the OpenID endpoint becomes available.
• Document the retry behavior in the JWT operator guide and add a changelog entry.

Custom instructions used:

• .github/copilot-instructions.md
• .github/instructions/reviewing.instructions.md
• .github/instructions/changelog.instructions.md

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
src/node/jwt_key_auto_refresh.h	Adds per-issuer retry scheduling with exponential backoff and cancellation on success/issuer removal/role change.
tests/jwt_test.py	Extends the connection-failure test to start the issuer after an initial failure and assert refresh recovery.
doc/build_apps/auth/jwt.rst	Documents the new retry + exponential backoff behavior.
CHANGELOG.md	Records the user-visible behavior change for JWT auto-refresh retries.

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