This article explores the importance of proper token validation in serverless architectures, focusing on Amazon Cognito JWT tokens. It demonstrates how manipulating Cognito access tokens can lead to unauthorized access of user data in a vulnerable application. The author explains the structure of JWT tokens and shows how changing the payload can bypass authentication if not properly validated. The article highlights the need for multiple security layers, including API Gateway authorizers and server-side token validation. It provides a step-by-step guide on implementing a Cognito Authorizer in API Gateway to address the vulnerability. Additionally, it offers an alternative solution of token signature validation within Lambda function code. The article emphasizes the critical nature of this security measure in protecting against unauthorized access and data exposure in serverless applications.