When you use AWS Cognito User Pools to authenticate a user, the typical flow involves several steps where the user is authenticated, and tokens are issued and utilized. Here’s a step-by-step breakdown of this process:
- User Registration/Sign-up: The user signs up using their username and password, or through a third-party identity provider supported by Cognito.
- User Sign-in: Upon successful sign-up, the user signs in. This can be done using a standard authentication flow (username and password) or through federated sign-in via external identity providers integrated with Cognito.
- Authentication Challenge: Depending on the user pool's security configuration, the user may be required to respond to various challenges (like MFA or CAPTCHA) before authentication is confirmed.
Once the user is authenticated:
- ID Token: This JWT (JSON Web Token) contains claims about the identity of the authenticated user such as the user’s name, email, and groups they belong to. It is used to assert the identity of the user.
- Access Token: This token is also a JWT and is used to authorize access to a resource. It contains scopes and other access privileges.
- Refresh Token: This is used to obtain new ID and access tokens once the original tokens expire without requiring the user to authenticate again.
- Token Storage: Where these tokens are stored depends on the client application’s architecture. In web applications, tokens might be stored in web storage (local storage or session storage). For mobile applications, tokens could be stored securely in keychain storage (iOS) or SharedPreferences (Android). It’s crucial to handle token storage securely to prevent vulnerabilities such as XSS or CSRF attacks.
- Token Usage: When the client makes requests to resources (like an API Gateway or some AWS service), the access token is included in the authorization header of the HTTP request. This allows the service to verify the token and determine if the client should be allowed access to the requested resources.
- Refresh Process: When the ID and access tokens expire, the client application can use the refresh token (if it hasn't expired) to request new tokens from Cognito without needing the user to re-authenticate. This is typically handled automatically by most client SDKs provided by AWS.
This flow ensures that user authentication and authorization are handled securely and efficiently, with AWS Cognito handling much of the complexity involved in managing these processes.