baton-github: override static token with reuseToken in appClient

[Bencheng21]

Description

Before the fix

After the fix

Summary by CodeRabbit

• Bug Fixes
  • Improved app-based authentication to ensure tokens are properly refreshed during use, preventing potential authentication failures due to token expiration.

[coderabbitai]

Walkthrough

Refactors JWT token sourcing in the connector by introducing a reusable token source and app JWT token refresher. The installation token flow now derives from refreshed app JWT tokens instead of one-shot tokens, with appClient overridden to use the shared jwtts token source.

Changes

Cohort / File(s)	Summary
JWT Token Source Refactoring pkg/connector/connector.go	Introduces reusable jwtts token source with app JWT token refresher. Replaces inline token source in jwtTokenSource and overrides appClient to use jwtts, aligning app-based authentication with token refresh mechanics.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Poem

🐰 A token once rigid, now fluid and free,
Through refresh mechanics, a harmony!
The app JWT dances with sources anew,
Installation flows blessed with a better view! ✨

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: replacing a static token with a reusable token source in appClient, which aligns with the AI-generated summary of introducing jwtts and overriding appClient.

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✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch ben/refresh_jwttoken

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[Bencheng21]

looks like line 305 - 344 is unnecessary, but need to investigate why it's there.