Implements client registration, authorization code flow with PKCE (S256), access/refresh token generation/verification, and cleanup utilities. Follows TDD — all 12 service-level tests pass. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Implements client registration, authorization code flow with PKCE (S256), access/refresh token generation/verification, and cleanup utilities. Follows TDD — all 12 service-level tests pass. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>