Manual Authentication with Amazon Cognito

Question

I know of two ways to authenticate as a user and obtain the access token , one is through the Hosted UI and another with various provided SDKs .

What I'm looking for is an endpoint obtain the access token directly with user credentials.

POST https://that-special-endpoint.com/login
{
 username: "example@email.com",
 password: "Abc123456",
 ...client ID, etc.
}

I've searched for some time but could not find how to do this. Is this not possible due to some security concerns that I'm not aware of?

I did consider creating a Lambda API and make use of the Cognito SDK to cater for my use case but I'm not sure if it's advisable...

Answer 1

Similar question is answered here . You can access https://cognito-idp.[region].amazonaws.com/ to call InitiateAuth and RespondToAuthChallenge APIs.

---

InitiateAuth

---

1. Create a json file, aws-auth-data.json

{
    "AuthParameters": {
        "USERNAME": "your-email@example.com",
        "PASSWORD": "your-first-password",
        "SECRET_HASH": "......(required if the app client is configured with a client secret)"
    },
    "AuthFlow": "USER_PASSWORD_AUTH",
    "ClientId": "5m........................"
}

2. Send a request on https://cognito-idp.us-east-2.amazonaws.com/ (if the user pool is on us-east-2 region) to call InitiateAuth API and initiate an authentication flow.

curl -X POST --data @aws-auth-data.json \
-H 'X-Amz-Target: AWSCognitoIdentityProviderService.InitiateAuth' \
-H 'Content-Type: application/x-amz-json-1.1' \
https://cognito-idp.us-east-2.amazonaws.com/

3. Then you'll get the user's tokens.

{
    "AuthenticationResult": {
        "AccessToken": "eyJra........",
        "ExpiresIn": 3600,
        "IdToken": "eyJra........",
        "RefreshToken": "eyJjd........",
        "TokenType": "Bearer"
    },
    "ChallengeParameters": {}
}

---

RespondToAuthChallenge

---

You may get a challenge as InitiateAuth response. For example, you will be asked to change password when you make a first 'InitiateAuth' attempt:

{
    "ChallengeName": "NEW_PASSWORD_REQUIRED",
    "ChallengeParameters": {
        "USER_ID_FOR_SRP": "abababab-......",
        "requiredAttributes": "[]",
        "userAttributes": "{\"email_verified\":\"true\",\"email\":\"your-email@example.com\"}"
    },
    "Session": "DNdY......"
}

In this case, change the password with RespondToAuthChallenge and you will get tokens.

{
    "ChallengeName": "NEW_PASSWORD_REQUIRED",
    "ChallengeResponses": {
        "USERNAME": "your-email@example.com",
        "NEW_PASSWORD": "your-second-password"
    },
    "ClientId": "5m........................",
    "Session": "DNdYN...(what you got in the preceding response)"
}

curl -X POST --data @aws-change-password.json \
-H 'X-Amz-Target: AWSCognitoIdentityProviderService.RespondToAuthChallenge' \
-H 'Content-Type: application/x-amz-json-1.1' \
https://cognito-idp.us-east-2.amazonaws.com/

See also:

https://docs.aws.amazon.com/cognito-user-identity-pools/latest/APIReference/API_InitiateAuth.html

https://docs.aws.amazon.com/cognito-user-identity-pools/latest/APIReference/API_RespondToAuthChallenge.html

https://docs.aws.amazon.com/cognito/latest/developerguide/amazon-cognito-user-pools-authentication-flow.html#amazon-cognito-user-pools-client-side-authentication-flow