27.5. Authentication and Authorization in APIs with API Gateway and Lambda: Using JWT Tokens for Authentication and Authorization

Authentication and authorization are fundamental parts of any application. They ensure that the user is who they say they are (authentication) and that they have permission to do what they are trying to do (authorization). In the context of REST APIs, this is especially important as these APIs are often exposed on the internet and are therefore potential targets for abuse.

A common way to implement authentication and authorization in REST APIs is using JWT tokens (JSON Web Tokens). JWT is an open standard that defines a compact, independent way to transmit information between parties as a JSON object. This information can be verified and trusted because it is digitally signed. JWTs can be signed using a secret (with the HMAC algorithm) or a public/private key pair using RSA or ECDSA.

In a typical scenario, the user authenticates by providing credentials, such as a username and password. If the credentials are correct, the server generates a JWT token and sends it back to the client. The client then includes this token in each subsequent request to the server. The server checks the token and, if it is valid, processes the request. If the token is not valid (for example, it is expired), the server rejects the request.

Authentication and Authorization with API Gateway and Lambda

AWS API Gateway and AWS Lambda are two powerful services that can be used to create and host REST APIs. They also support authentication and authorization using JWT tokens.

API Gateway can be configured to require a JWT token for certain routes. This is done using a feature called 'JWT Token Authorizers'. A JWT Token Authorizer is a Lambda function that receives a JWT token, checks its validity, and returns an access policy that specifies what actions the token holder is authorized to perform.

Here's an example of how this might work:

1. The client authenticates by providing its credentials.
2. The server checks the credentials and, if they are correct, generates a JWT token and sends it back to the client.
3. The client includes the JWT token in each subsequent request to the server.
4. API Gateway receives the request and extracts the JWT token.
5. API Gateway calls the JWT Token Authorizer Lambda function, passing the JWT token as an argument.
6. The Lambda function checks the validity of the JWT token. If the token is valid, the Lambda function returns an access policy that specifies what actions the token holder is authorized to perform.
7. API Gateway checks the access policy returned by the Lambda function. If the policy allows the requested action, API Gateway processes the request. If the policy does not allow the requested action, API Gateway rejects the request.

This process ensures that only authenticated users with appropriate permissions can access your REST APIs.

Conclusion

Authentication and authorization are fundamental parts of any application and using JWT tokens is an effective way to implement these functionalities in REST APIs. AWS API Gateway and AWS Lambda provide robust support for authentication and authorization using JWT tokens, making them an excellent choice for developing secure REST APIs.