feat(introspection): return structured failure details

[shreemaan-abhishek]

Summary

• extend introspect with an additive raw endpoint status and structured failure result while preserving its existing first two return values
• distinguish invalid requests and tokens from unavailable endpoints, invalid responses, and configuration errors
• preserve structured failure details when concurrent requests share a non-cacheable introspection result, while retaining direct introspection fallback when coordination fails

Fixes #574

Checklist

• Tests pass with docker build -f tests/Dockerfile . -t lua-resty-openidc/test
• Tests pass with docker run -t --rm lua-resty-openidc/test:latest
• ChangeLog is updated for behavior changes, bug fixes, features, or user-visible documentation changes

[shreemaan-abhishek]

@kevinlzw could you please review this PR?

[kevinlzw]

Thanks for the PR. I reviewed the diff and have two non-blocking suggestions:

1. Could we add coverage for the new return values on cache hits and coalesced requests? In particular, a negative-cache hit should retain invalid_token/401, and waiters sharing an endpoint failure should receive the same endpoint_status and failure details as the initiating request. The current concurrent test checks the response status and failure kind, but not the third return value.

2. Could we also mention the stricter boolean validation of active in the ChangeLog? Previously, truthy non-boolean values such as "true" or 1 could be accepted; they now produce invalid_response. This is a useful validation change, but it is an observable behavior change beyond adding return values.

I haven't rerun the tests locally; this review is based on the code and test changes, with CI passing.

Also, I'll be on vacation for about two weeks, so my replies may be slower during that time. Thanks for your patience!

[shreemaan-abhishek]

Thanks, both suggestions are addressed in eca4a7f.

[shreemaan-abhishek]

Enjoy your vacation, thanks a lot!

[kevinlzw]

Thanks for addressing both suggestions. The negative-cache and coalesced-failure tests now cover the additional return values, and the ChangeLog documents the stricter boolean active validation. Reviewed eca4a7f; CI is passing. I have not rerun the tests locally. Looks good to me.

[shreemaan-abhishek]

thank you, if you can, please let us know when will the next release be conducted?