fix: offload blocking Keycloak introspect to thread pool

[suhr25]

Summary
Fixes a performance issue where blocking I/O was executed inside async code, causing the event loop to stall under load.

Problem

• In src/authentication.py, _get_user() called keycloak_openid.introspect(token), which uses synchronous requests, blocking the asyncio event loop.
• In src/middleware/access_log.py, a synchronous DB sess.commit() ran inside async middleware, blocking request handling.

Fix

1. Offload Keycloak introspection to a thread pool

loop = asyncio.get_running_loop()
userinfo = await loop.run_in_executor(None, keycloak_openid.introspect, token)

2. Move access log DB write to a background task

response.background = BackgroundTask(
    _write_access_log, resource_type, asset_id, response.status_code
)

Verification

• Existing tests pass without modification
• Mocked introspect() works correctly with executor
• Concurrent requests no longer block each other
• Access logs are still written correctly
• Load testing shows reduced latency and improved throughput under concurrency

[suhr25]

Hi @geetu040,
Fixed event loop blocking by offloading the Keycloak introspection call to a thread pool and moving the DB write to a background task. This restores proper async behavior and improves performance under load without changing functionality.

[suhr25]

Hi @geetu040 @fkiraly,
Just noticed the workflow is awaiting approval, so CI hasn’t run yet.
Would appreciate approval when possible. Thank you!

[suhr25]

Hi @geetu040,
Please let me know if any change is needed or it is ready to merge?

[suhr25]

Hi @geetu040 @fkiraly,
Can you please review this PR.
Thanks!