This is why a quarterly check-in is not optional. Oauth 2.0 is the gatekeeper for APIs, microservices, and SSO. When it drifts, small misconfigs become outages. A disciplined review every quarter catches them before they burn you.
Start with your authorization server. Verify supported grant types match current usage. If you have unused flows, remove them. Limit scope definitions to the smallest set needed. Any extra is an attack surface. Check refresh token lifetimes against your policy. Are revoked tokens truly invalidated? Test it.
Audit client registrations. Rotate client secrets. Remove any stale apps. Inspect redirect URIs—no wildcards, no test endpoints left in place. Make sure PKCE is enforced for public clients. These steps block common exploits.
Review logging and metrics. You need visibility across token issuance, refresh, and revocation. Enable anomaly detection for unusual patterns like too many refreshes in a short window. Strong monitoring is a fast tripwire.