The token exchange request was missing the required grant_type parameter
per OAuth 2.0 RFC 6749. IndieAuth providers that properly validate this
were rejecting the request with a 422 error.
- Add grant_type=authorization_code to token exchange data
- Add ADR-022 documenting the spec compliance requirement
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
