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Asked: 2024-09-21T16:46:17+05:30 In:

How can I customize the response message and status code from an API Gateway custom authorizer in AWS? I’m looking for guidance on how to achieve this effectively.

Hey everyone!

I’m currently working on an API Gateway project in AWS, and I’m using a custom authorizer for authentication. I’ve hit a bit of a snag and could really use your expertise.

Specifically, I’m trying to figure out how to customize the response messages and status codes that are sent back from the API Gateway when the custom authorizer validates (or rejects) a request. I want to make sure that the clients get meaningful feedback depending on the outcome, but I’m not sure of the best approach to achieve this.

Has anyone here successfully implemented this? Any detailed steps or examples would be super helpful! Thanks in advance for your assistance!

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    3 Answers



    1. API Gateway Custom Authorizer Response Customization

      Customizing Response Messages in AWS API Gateway

      Hi there!

      I’ve run into the same challenge while working with a custom authorizer in AWS API Gateway, and I’d be happy to share what I learned.

      Custom Authorizer Setup

      Your custom authorizer will have the ability to validate requests by returning an allow or deny policy. However, to customize the responses and status codes, you will need to handle this in the integration response of your API Gateway setup.

      Steps to Customize Responses:

      1. Implement Custom Logic in Authorizer: When your authorizer evaluates a request, you can return detailed error messages by setting context properties in the response object. For example:
        2. {
  "principalId": "user|a1b2c3d4",
  "policyDocument": {
    "Version": "2012-10-17",
    "Statement": [
      {
        "Action": "execute-api:Invoke",
        "Effect": "allow",
        "Resource": "arn:aws:execute-api:region:account-id:api-id/stage/method/resource"
      }
    ]
  },
  "context": {
    "message": "Authorization successful!",
    "code": 200
  }
}
      2. Mapping Authorizer Response: In your API’s Integration Response settings, you can map these context variables to the HTTP response status code and body. For example, you can set up a mapping template to return custom messages based on the context properties.
      3. Configure Integration Response: Go to the Integration Response of your API Gateway and create a method response. Map responses based on the context.code from the authorizer. You will need conditions in your response based on the value in context.
      4. Returning Errors: If an error occurs (e.g., validation failed), you can simply return a deny policy and also add a specific status code and message to provide useful feedback to clients.
        5. {
  "principalId": "user|a1b2c3d4",
  "policyDocument": {},
  "context": {
    "message": "Unauthorized: Invalid token",
    "code": 401
  }
}

      Testing your Setup

      After all configurations, be sure to test your API with various valid and invalid tokens to verify that the responses return meaningful information based on your logic.

      I hope this helps you implement a more user-friendly feedback mechanism in your API! If you have any further questions, feel free to ask!

      Good luck with your project!




    2. API Gateway Custom Authorizer Help

      API Gateway Custom Authorizer – Response Customization

      Hey there!

      It sounds like you’re diving into quite an interesting project! Customizing the response messages and status codes for your API Gateway using a custom authorizer can certainly improve the user experience. Here are some steps and tips that might help you achieve this:

      1. Custom Authorizer Function

      First, ensure your custom authorizer is set up correctly. It should validate the incoming request (e.g., checking a token) and return a proper response. Here’s a basic outline of what your authorizer function might look like:

      
exports.handler = async (event) => {
    const token = event.authorizationToken;

    // Perform your token validation logic here
    if (isValidToken(token)) {
        return generateAllow('user', event.methodArn);
    } else {
        return generateDeny('user', event.methodArn);
    }
};

const generateAllow = (principalId, resource) => {
    return {
        principalId,
        policyDocument: {
            Version: '2012-10-17',
            Statement: [{
                Action: 'execute-api:Invoke',
                Effect: 'Allow',
                Resource: resource,
            }]
        }
    };
};

const generateDeny = (principalId, resource) => {
    return {
        principalId,
        policyDocument: {
            Version: '2012-10-17',
            Statement: [{
                Action: 'execute-api:Invoke',
                Effect: 'Deny',
                Resource: resource,
            }]
        }
    };
};

const isValidToken = (token) => {
    // Your validation logic here
    return token === 'your-valid-token';
};

      2. Customize Gateway Responses

      To customize the responses from your API Gateway, you can create Gateway Response settings in your API configuration. AWS API Gateway allows you to define specific responses for unauthorized requests.

      Example of Custom Gateway Responses:

      • Go to your API Gateway console.
      • Select your API and then click on “Gateway Responses.”
      • Add a new Response Type or edit the existing “DEFAULT_4XX” or “DEFAULT_5XX” responses.
      • In the Response Headers and Response Template sections, you can define the message format and content.

      3. Defining Custom Status Codes

      You can configure specific status codes depending on the outcome of your authorizer validation. For instance, if a token is invalid, you can return a 403 status code by modifying your authorizer to send the appropriate response:

      
if (!isValidToken(token)) {
    throw new Error('Unauthorized'); // This can trigger a 403 response
}

      4. Testing and Iterating

      After implementing these changes, use tools like Postman or Curl to test your API. Make sure to test with valid and invalid tokens to see the different response messages and statuses.

      Remember, customization can be a bit tricky as you’re learning, but experimenting will definitely help you understand it better. Don’t hesitate to reach out with specific details if you run into roadblocks or need further clarification!

      Good luck, and happy coding!



    3. To customize the response messages and status codes in AWS API Gateway when using a custom authorizer, you’ll want to leverage the integration response settings of the API Gateway along with the Lambda function implementing your custom authorizer. When your authorizer Lambda function runs, it can return a policy document along with context data, but if you want to modify the response further based on validation results, you will need to include additional logic in your Lambda function. For instance, upon successful validation, you can return a custom message in the context object, which can then be mapped to your API Gateway’s response using integration response mapping templates. You can achieve this by setting up a mapping template in the Integration Response section of your API Gateway method that transforms the output based on the context data sent from the authorizer.

      In addition to integrating custom success messages, you can also handle rejections and errors in a user-friendly manner. For instance, if your authorizer detects an unauthorized request, you can throw an error or reject with a specific message that indicates the reason for rejection, such as “Invalid token” or “User not authorized.” In the API Gateway, configure the Method Response and Integration Response to capture these specific error messages and status codes (like 401 for Unauthorized or 403 for Forbidden). By setting this up, clients interacting with your API will receive meaningful feedback tailored to the outcome of their requests, enhancing the overall user experience and ease of debugging.


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