ClientID

A ClientID is a public identifier assigned to an application or client by an authorization server or API provider during the client registration process. It is used to identify the application to the authorization server and to the service handling API access.

Typically, the ClientID is a non-secret string, such as a UUID or alphanumeric token. It is designed to be exposed in requests, user interfaces, and browser-based flows. By itself, the ClientID does not prove the identity of the client or grant access; it simply identifies which application is making a request.

In OAuth 2.0 and OpenID Connect, the ClientID is included in authorization requests to indicate which application is requesting access or initiating an authentication flow. The authorization server uses the ClientID to apply registered settings, such as allowed redirect URIs, permitted scopes, and consent requirements. The server may return authorization codes or tokens tied to that client identifier.

The ClientID is distinct from the client secret. The client secret is a confidential credential used to authenticate the client during token requests, typically in server-side or confidential client scenarios. Public clients, such as single-page apps or mobile apps, often do not have a client secret and rely on other security measures like PKCE.

Registration and management involve submitting application details (name, redirect URIs, potentially branding or contact information) to the identity provider or API service. The provider issues a ClientID and may also provide a client secret or other credentials, along with management options and usage policies.

Security considerations emphasize that the ClientID alone does not authorize access. Proper use of redirect URIs, state parameters, PKCE, and secure token handling remains essential to protect the flow.