OpenID Connect (OIDC) is a widely used client authentication method for Couchbase Sync Gateway, facilitating the synchronization of Couchbase Lite clients, web frontends, or mobile apps. The system uses OIDC Implicit Flow for authentication, which is simpler than the Authorization Code flow and involves embedding an ID token as a Bearer token or using a session ID for replication processes. Configuration involves setting up Couchbase Sync Gateway for OIDC authentication by specifying providers, client IDs, and registration options. On startup, Sync Gateway fetches metadata from the OIDC provider's discovery endpoint to validate tokens, using either offline mode for ID token validation or session cookies for continuous sessions. Users can be automatically created on Sync Gateway if they do not exist, but they are initially without specific access grants. Access grants to documents can be managed dynamically or statically, ensuring that users only see content they have permissions for. Changes in user access or deletion during replication can impact the replication process, terminating it if necessary. Future posts promise to explore the Authorization Code Flow within Sync Gateway.