Worked on the cloudflare/workers-oauth-provider repository to enhance the OAuth token exchange flow, focusing on improving concurrency safety and robustness. Introduced a grantId field to TokenExchangeCallbackOptions, enabling precise identification and revocation of specific grants during concurrent operations. Applied this enhancement across all relevant token exchange scenarios, including authorization_code, refresh_token, and token_exchange flows, addressing a critical race condition in grant revocation. Augmented the TypeScript test suite to ensure grantId consistency and documented usage patterns for downstream consumers. Maintained full backward compatibility, allowing existing API implementations to function without modification. Utilized TypeScript and API development best practices throughout the work.