Software⏱️ 4 min read📅 2026-06-03

How to Fix: Missing Authentication Token while accessing API Gateway?

API Gateway requires AWS_IAM authentication with a valid token to secure API calls.

Quick Answer: Ensure your IAM user has the AmazonAPIGatewayInvokeFullAccess policy and is assigned an IAM role that includes the necessary permissions for your Lambda function.

📋 Table of Contents

  1. 💡 Why You Are Getting This Error
  2. ✅ Best Solutions to Fix It
  3. ✨ Wrapping Up

The 'Missing Authentication Token' error occurs when an API Gateway request is made without providing the required AWS IAM authentication token. This issue affects developers who have integrated their Lambda functions with API Gateway and are using AWS IAM for authentication.

This error can be frustrating as it prevents access to the API, even for authorized users. However, by following the steps outlined in this guide, you should be able to resolve the issue and secure your API calls.

💡 Why You Are Getting This Error

  • The primary reason for this error is that the AWS IAM authentication token is not being passed correctly from the client-side application to the API Gateway. This can happen when the 'Authentication type' is set to AWS_IAM, but the policy attached to the user does not include the necessary permissions.
  • An alternative reason could be that the Lambda function is not configured to expect the AWS IAM authentication token in its environment variables.

✅ Best Solutions to Fix It

Configuring API Gateway to Expect AWS IAM Authentication Token

  1. Step 1: Step 1: Navigate to your API Gateway and select the 'Method' that is causing the error. Click on the 'Integration Request' tab and then click on the 'Advanced' button.
  2. Step 2: Step 2: In the 'Advanced' window, scroll down to the 'Request Parameters' section and add a new parameter named 'X-Amz-Security-Token'. Set its data type to 'String' and leave the default value as an empty string.
  3. Step 3: Step 3: Save your changes and then test the API Gateway again. The AWS IAM authentication token should now be passed correctly, and you should no longer receive the 'Missing Authentication Token' error.

Configuring Lambda Function to Expect AWS IAM Authentication Token

  1. Step 1: Step 1: Navigate to your Lambda function in the AWS Management Console. Click on the 'Function code' tab and then click on the 'Environment variables' button.
  2. Step 2: Step 2: In the 'Environment variables' window, add a new variable named 'AWS_ACCESS_KEY_ID'. Set its value to the access key ID of the IAM user that is attached to your API Gateway.
  3. Step 3: Step 3: Add another environment variable named 'AWS_SECRET_ACCESS_KEY' with the secret access key of the IAM user. Save your changes and then test your Lambda function again. The AWS IAM authentication token should now be passed correctly, and you should no longer receive the 'Missing Authentication Token' error.

✨ Wrapping Up

By following these steps, you should be able to resolve the 'Missing Authentication Token' error and secure your API calls using AWS IAM authentication. Remember to always verify that your IAM user has the necessary permissions attached to it, and that the Lambda function is configured correctly to expect the AWS IAM authentication token.

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