OAuth 2.0: The Foundation

• Authorization, not Authentication:

  OAuth 2.0 primarily focuses on authorization, determining which applications have access to user data. It doesn’t handle the actual login process (authentication), which is often handled separately. 
• Delegated Access:

  OAuth 2.0 allows users to grant specific permissions to third-party applications, such as accessing their email, social media data, or other protected resources. 
• Access Tokens:

  The core of OAuth 2.0 is the use of access tokens, which are short-lived credentials used to verify access to protected resources. 
• Authorization Server:

  An authorization server manages the OAuth 2.0 flow, issuing and managing access tokens. 
• Resource Server:

  The resource server provides access to the protected resources. 
• Client Application:

  The client application, like a web or mobile app, requests access to resources. 

OpenID Connect (OIDC): Adding Authentication

• Building on OAuth 2.0:

  OIDC builds upon OAuth 2.0, adding a layer of authentication to identify the user making the request.
• User Information:

  OIDC provides mechanisms to retrieve user information, such as their ID, email, and other attributes.
• Identity Provider (IdP):

  OIDC relies on an identity provider (IdP) to handle authentication and issue user identification tokens.
• JSON Web Tokens (JWT):

  OIDC often uses JWTs for authentication and authorization, providing a standardized format for exchanging user information securely. 

Beyond OAuth 2.0 and OIDC: Advanced Security

• API Gateways:

  Using an API gateway provides a centralized point for managing security policies, including OAuth 2.0 and OIDC, and implementing additional security measures like rate limiting and request filtering. 
• JWT Verification:

  Validating JWTs received from an API request is crucial for verifying the identity and authorization of the user or application. 
• Token Rotation and Revocation:

  Implement mechanisms for rotating access tokens and revoking them if necessary, for example, when a user’s account is compromised. 
• HTTPS and Transport Layer Security (TLS):

  Ensure that all communication between clients, authorization servers, and resource servers uses HTTPS to encrypt sensitive data in transit. 
• Principle of Least Privilege:

  Grant applications only the necessary permissions to access specific resources, minimizing the potential impact of a security breach. 
• Monitoring and Logging:

  Implement robust monitoring and logging to detect and respond to security incidents, including unauthorized access attempts. 

Example Scenario: Securing a REST API

1. 1. User Authentication:

   A user authenticates with an OIDC-compliant IdP (e.g., Auth0).
2. 2. IdP Issues ID Token:

   The IdP issues an ID token, containing user information, which is then returned to the client application.
3. 3. Client Requests Access Token:

   The client application uses the ID token to request an access token from the authorization server (e.g., using the authorization code grant flow).
4. 4. Authorization Server Issues Access Token:

   The authorization server validates the ID token, issues an access token, and returns it to the client application.
5. 5. Client Makes API Request:

   The client application includes the access token in an API request to the resource server (e.g., using the “Bearer” authentication scheme).
6. 6. Resource Server Validates Token:

   The resource server validates the access token, ensuring it is valid and has the necessary permissions.
7. 7. Resource Server Serves Data:

   If the token is valid, the resource server provides the requested data to the client application.