Client ID

Overview

Client ID is a public identifier assigned to an OAuth client so the authorization server can distinguish the requesting application and apply its registered configuration. A client ID identifies the client but is not normally a secret and must not be treated as proof that the caller is legitimate.

Key risks include client impersonation assumptions, shared IDs across unrelated applications, stale registrations, redirect URI abuse, mix-up across authorization servers, and accidental exposure of production configuration in test code. Changes to Client ID should preserve overlap or recovery where required while preventing old credentials from remaining active indefinitely.

A production implementation should bind it to exact redirect URIs and allowed grant types, separate environments, inventory ownership, validate issuer context, and retire unused registrations. For Client ID, secrets and tokens should remain outside browser bundles, URLs, ordinary logs, and unprotected configuration.

Useful measures include active client registrations, unused-client age, invalid client errors, redirect mismatches, environment-crossing attempts, and registrations without owners. Client ID is closely connected to OAuth 2.0, Client Secret, and Authorization Endpoint. Monitoring for Client ID should track failed use, unusual scope or audience, expiry, rotation status, and attempts involving revoked credentials.

The Client ID recovery process should restore access without bypassing the original identity and authorization controls. Least-privilege configuration for Client ID should be verified against the operations used by each environment and consuming service.

A compromise response for Client ID should support rapid revocation, replacement, affected-client identification, and review of prior use. The Client ID boundary should identify the principal, credential or key, permitted audience, scope, lifetime, and revocation path.