How to Simulate Cognito Login in Postman

When you're testing a backend system protected by AWS Cognito, one of the first practical challenges is obtaining a valid authentication token without going through your frontend app. You need to call the Cognito identity provider directly, and that requires understanding two things: the Cognito authentication flow, and how AWS Signature Version 4 (SigV4) authorization works in Postman. This post walks through the exact setup, from IAM credentials to a working 200 OK with an AccessToken in hand. Prerequisites Before you start, make sure you have the following: Access to the AWS Console with permissions to view Cognito and IAM The AWS region where your Cognito User Pool is deployed (e.g., us-east-2 ) An IAM user with programmatic access — you will need the Access Key ID and Secret Access Key Your Cognito App Client ID — found under your User Pool > App clients A test user account in the User Pool with known credentials USER_PASSWORD_AUTH enabled on the App Client (more on this below) A