HttpListenerException "access denied" using GoogleWebAuthorizationBroker.AuthorizeAsync

Question

HttpListenerException "access denied" using GoogleWebAuthorizationBroker.AuthorizeAsync

I am trying to run OAuth2 using web applications hosted on Azure and cannot use service accounts (several solutions are available here, but they are all tied to service accounts / certificates), while I need a user for authentication and Log in with Google.

The code:

var credential = GoogleWebAuthorizationBroker.AuthorizeAsync(
    new ClientSecrets { ClientId = _clientId, ClientSecret = _clientSecret },
    scopes,
    User.Identity.Name,
    CancellationToken.None,
    new FileDataStore("GA.Auth.Store")) /* tried this to be null as well */
    .Result;

var service = new AnalyticsService(
    new BaseClientService.Initializer()
    {
        HttpClientInitializer = credential,
        ApplicationName = "Analytics API Sample"
    });

It works locally, but throws this exception when deployed as an Azure web application:

[HttpListenerException (0x5): Access is denied]
Microsoft.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) +82
Microsoft.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccess(Task task) +76
Google.Apis.Auth.OAuth2.<AuthorizeAsync>d__1.MoveNext() +233