AuthorizationServer

An AuthorizationServer is a component in OAuth 2.0 and OpenID Connect architectures that authenticates resource owners and issues access tokens to clients after the resource owner's authorization. It sits between the client application and the resource server, and its primary function is to grant access to protected resources by presenting tokens that prove authorization.

Interaction typically involves the resource owner authenticating with the AuthorizationServer, a client requesting access through an authorization grant at the authorization endpoint, and the client exchanging the grant at the token endpoint for an access token (and optionally a refresh token and an ID token). The server validates the client, the redirect URI, and the grant before issuing tokens.

Tokens include access tokens, refresh tokens, and, in OpenID Connect, ID tokens. Access tokens authorize resource server access, while refresh tokens enable obtaining new access tokens without re-authenticating. Token formats may be opaque or JWT. Security considerations include using PKCE for public clients, short token lifetimes, token revocation, scope restriction, and audience binding.

Endpoints commonly supported by an AuthorizationServer include the authorization endpoint and the token endpoint, with optional endpoints for token revocation, introspection, and user information retrieval. OpenID Connect adds an ID token and user info endpoints. Adjustments for security and privacy are important, such as consent screens and proper storage of client credentials.

Implementation and deployment vary; servers implement different grant types, including authorization code, client credentials, and, for legacy clients, resource owner password credentials. Best practices emphasize minimal privilege scopes, secure storage of secrets, and regular audits to maintain compliance with OAuth 2.0 and OpenID Connect specifications.