How to get REFRESH_TOKEN_AUTH request to return RefreshToken

Question

I am using Amazon Cognito to login users and save a RefreshToken so they don't have to type their password after the initial setup. I need to be able to login with the RefreshToken and get a new RefreshToken to save for next time. However, when I call InitiateAuthAsync, it does not return the RefreshToken.

C#:

var refreshReq = new InitiateAuthRequest();
refreshReq.ClientId = _clientId;

refreshReq.AuthFlow = AuthFlowType.REFRESH_TOKEN_AUTH;
refreshReq.AuthParameters.Add("SECRET_HASH", 
    SecretHash(_clientId, _clientSecret, username));
refreshReq.AuthParameters.Add("REFRESH_TOKEN", refreshToken);


var clientResp = cognitoProvider.InitiateAuthAsync(refreshReq).Result;

Response:

{
    "AuthenticationResult": {
        "AccessToken": "<accessToken>",
        "ExpiresIn": 3600,
        "IdToken": "<idToken>",
        "TokenType": "Bearer"
    },
    "ChallengeParameters": {}
}

And this is the response from the login with a working ResponseToken:

{
    "AuthenticationResult": {
        "AccessToken": "<accessToken>",
        "ExpiresIn": 3600,
        "IdToken": "<idToken>",
        "RefreshToken": "<refreshToken>",
        "TokenType": "Bearer"
    },
    "ChallengeParameters": {}
}

Answer 1

Apparently this is a bug in the AWS Cognito API. The docs say that InitiateAuth should return an updated RefreshToken, but it does not.