Unable to get IAM security credentials from EC2 Instance Metadata Service error when using Aws Sdk in UWP - wpf

Question

I'm working with Aws Sdk and I'm trying to implement a login UI using UWP. I followed this online tutorial (which is for WPF) and I tried to make it works for the Universal Windows Platform as well.
The core part of the source code is the following (please note that is 90% similar to the one posted in the tutorial. The "only difference" is that I used
InitiateAuthAsync
instead of
AdminInitiateAuthAsync
<!-- language: lang-cs -->
private readonly AmazonCognitoIdentityProviderClient _client;
private readonly string _clientId = "32fsoifj93fjsiispat";
public MainPage()
{
this.InitializeComponent();
var amazonCognitoIdentityProviderConfig = new AmazonCognitoIdentityProviderConfig();
amazonCognitoIdentityProviderConfig.ServiceURL = "https://cognito-idp.eu-central-1.amazonaws.com/";
_client = new AmazonCognitoIdentityProviderClient(amazonCognitoIdentityProviderConfig);
}
private async Task<bool> CheckPasswordAsync(string userName, string password)
{
try
{
List<HttpHeader> httpHeaders = new List<HttpHeader>();
HttpHeader httpHeader = new HttpHeader
{
HeaderName = "X-Amz-Target",
HeaderValue = "AWSCognitoIdentityProviderService.InitiateAuth"
};
httpHeaders.Add(httpHeader);
httpHeader = new HttpHeader
{
HeaderName = "Content-Type",
HeaderValue = "application/x-amz-json-1.1"
};
httpHeaders.Add(httpHeader);
var authReq = new InitiateAuthRequest()
{
ClientId = _clientId,
AuthFlow = AuthFlowType.USER_PASSWORD_AUTH,
};
authReq.AuthParameters.Add("USERNAME", userName);
authReq.AuthParameters.Add("PASSWORD", password);
var authResp = await _client.InitiateAuthAsync(authReq);
return true;
}
catch (Exception ex)
{
return false;
}
}
Please consider that it is working properly with WPF framework. I'm able to get the TokenId and RefreshToken.
But if I try to copy and paste the same code in UWP I get the exception:
'Unable to get IAM security credentials from EC2 Instance Metadata Service.'
And if I try to investigate with Fiddler I get the following error:
[Fiddler] The connection to '169.254.169.254' failed. Error: NetworkUnreachable (0x2743). System.Net.Sockets.SocketException A socket operation was attempted to an unreachable network 169.254.169.254:80
I really can't understand why it tries to connect to the '169.254.169.254' address. Googling around I found other people experiencing the same issue (for example here). Do you have any idea?