… during authorization code exchange.

… during refresh token exchange.

… refreshAuthorization to maintain compatibility.

… into ochafik/auth-merge-531-552

…ods' into ochafik/auth-merge-531-552

The applyBasicAuth function was incorrectly trying to set headers using
array notation on a Headers object. Fixed by using the proper Headers.set()
method instead of treating it as a plain object.

This ensures that HTTP Basic authentication works correctly when
client_secret_basic is the selected authentication method.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>