AuthorizationEndpoint vs TokenEndpoint

In OAuth 2.0, the AuthorizationEndpoint and TokenEndpoint serve different roles in the process of obtaining access to resources on behalf of a user. Here's a breakdown of the differences between them:

1. Authorization Endpoint

• Purpose: The AuthorizationEndpoint is responsible for obtaining authorization from the user to access their resources. This is where the user grants permission to the client application (the one trying to access resources on behalf of the user).

• What Happens Here:

  • The client (e.g., a web or mobile app) redirects the user to the Authorization Server’s AuthorizationEndpoint.
  • The user authenticates (e.g., via login) and then authorizes the client to access specific resources.
  • If the authorization is successful, the server responds with an authorization code (in the case of the Authorization Code Flow) or directly with tokens (for other flows, such as Implicit Flow).

• When It’s Used:

  • Authorization Code Flow: This flow is used when the client needs to exchange an authorization code for tokens.
  • Implicit Flow: This flow is used primarily for single-page applications (SPAs) where tokens are returned directly from the AuthorizationEndpoint without needing to be exchanged via a server.

• Example Flow:

  • The user visits a website that requests access to their Google account.
  • The website redirects the user to Google’s AuthorizationEndpoint.
  • The user logs in, grants permission, and Google issues an authorization code back to the client.

• URL Example:
  
  

  https://authorization-server.com/oauth/authorize

2. Token Endpoint

• Purpose: The TokenEndpoint is responsible for exchanging an authorization code or other credentials (like client credentials or refresh tokens) for an access token (and possibly a refresh token and ID token). This token is what allows the client to access protected resources on behalf of the user.

• What Happens Here:

  • The client makes a POST request to the TokenEndpoint (usually after obtaining an authorization code from the AuthorizationEndpoint).
  • The client sends the authorization code, client credentials (client ID, client secret), and other required parameters.
  • If the request is valid, the server responds with an access token, which the client can use to access resources on the user's behalf.
  • In some cases, the TokenEndpoint also provides a refresh token for refreshing access tokens when they expire.

• When It’s Used:

  • Authorization Code Flow: After obtaining the authorization code, the client uses it to request an access token from the TokenEndpoint.
  • Client Credentials Flow: The client uses its own credentials to request an access token.
  • Refresh Token Flow: The client can use the TokenEndpoint to exchange a refresh token for a new access token when the original token expires.

• URL Example:
  
  

  https://authorization-server.com/oauth/token

Key Differences:

Example in OAuth 2.0 Authorization Code Flow:

1. Step 1: Authorization Endpoint:

   • The user is redirected to the AuthorizationEndpoint (e.g., Google’s OAuth page).
   • The user logs in and grants permissions.
   • The server sends back an authorization code to the client app.

2. Step 2: Token Endpoint:

   • The client sends a POST request to the TokenEndpoint, passing the authorization code.
   • The server verifies the authorization code and responds with an access token (and optionally a refresh token).
   • The client now uses this access token to access protected resources (like APIs) on behalf of the user.

Summary:

• The Authorization Endpoint is responsible for user interaction, where the user provides authorization for the client to access their resources.
• The Token Endpoint is responsible for issuing access tokens after verifying the client's authorization or credentials. It’s used in server-to-server communication to exchange authorization codes or refresh tokens for access tokens.