How to Fix AWS Cognito User Login Error

In this tutorial, you'll learn about How to Fix AWS Cognito User Login Error. We cover key concepts, practical examples, and best practices to help you understand and apply this topic effectively.

Users cannot log in through Cognito — NotAuthorizedException, UserNotFoundException, or InvalidParameterException — the authentication flow is misconfigured.

Step-by-Step Fix

1. Check user pool configuration

aws cognito-idp describe-user-pool --user-pool-id us-east-1_abc123

2. Verify app client settings

aws cognito-idp describe-user-pool-client --user-pool-id us-east-1_abc123 --client-id 1234567890abcdef

Ensure ExplicitAuthFlows includes the correct flows:

{
    "UserPoolClient": {
        "ClientName": "my-app",
        "ExplicitAuthFlows": [
            "ALLOW_USER_PASSWORD_AUTH",
            "ALLOW_REFRESH_TOKEN_AUTH]
        ]
    }
}

3. Update app client to allow password auth

aws cognito-idp update-user-pool-client --user-pool-id us-east-1_abc123 --client-id 1234567890abcdef --explicit-auth-flows ALLOW_USER_PASSWORD_AUTH ALLOW_REFRESH_TOKEN_AUTH

4. Initiate authentication

aws cognito-idp initiate-auth --auth-flow USER_PASSWORD_AUTH --auth-parameters USERNAME=user@example.com,PASSWORD=MyPassword123! --client-id 1234567890abcdef

Expected output:

{
    "AuthenticationResult": {
        "AccessToken": "eyJ...",
        "ExpiresIn": 3600,
        "IdToken": "eyJ...",
        "RefreshToken": "eyJ..."
    }
}

5. Handle forgot password flow

aws cognito-idp forgot-password --client-id 1234567890abcdef --username user@example.com

6. Confirm forgot password

aws cognito-idp confirm-forgot-password --client-id 1234567890abcdef --username user@example.com --confirmation-code 123456 --password NewPassword123!

Common Mistakes

Prevention

• Use the Cognito hosted UI for standard login flows.
• Enable advanced security features for compromised credential detection.
• Implement proper error handling in the client app.
• Use refresh tokens for persistent sessions.

Common Mistakes with cognito login

1. Overlapping type class instances that cause GHC to reject the program with ambiguous dispatch errors
2. Non-exhaustive pattern matches that compile with warnings then crash at runtime
3. Misunderstanding that String is [Char] with poor performance for large text operations

These mistakes appear frequently in real-world AWS code. DodaTech's contributors have identified these patterns through analysis of open-source projects and production systems.

Practice Exercise

Write a pure function that safely divides two integers using Maybe, then test it with edge cases like division by zero and negative numbers.

This exercise reinforces the concepts covered in this guide. Try implementing it before checking online solutions.

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