AWS API Gateway 403 Missing Authentication Token — What It Means & How to Fix It

Fix AWS API Gateway 403 Missing Authentication Token error when requests are sent to non-existent endpoints or without required authorization. This guide covers everything you need to know about this topic, including common causes, step-by-step solutions, and answers to frequently asked questions.

Here are the key things to understand: AWS API Gateway returns 403 Missing Authentication Token for requests to undefined routes, not just auth failures. Despite the error message, this often has nothing to do with authentication — it is a misleading error from API Gateway. The error occurs when the requested resource path or HTTP method does not match any deployed API route. It can also genuinely occur when a required authorizer (Lambda, Cognito, IAM) is not satisfied. Understanding these fundamentals will help you diagnose and resolve this issue more effectively.

The most common reasons this occurs include: Request sent to a URL path that does not exist in the API Gateway stage. API was not deployed after adding new routes — changes are not live yet. Incorrect stage name in the URL (e.g., /prod vs /staging). IAM authorization required but no SigV4 signature provided in the request. Identifying the root cause is the first step toward finding the right solution.

To resolve this, follow these recommended steps: Verify the exact URL path and HTTP method match a deployed route in API Gateway console. Deploy the API to the correct stage after making any route changes. Check the stage URL format: https://{api-id}.execute-api.{region}.amazonaws.com/{stage}/{path}. If using IAM auth, ensure the request includes valid AWS SigV4 authentication headers. If these steps do not resolve the issue, consider consulting additional resources or a qualified professional.

This article is part of our HTTP Status Codes collection on Error Codes Wiki. We provide comprehensive, up-to-date information to help you find solutions quickly.