Asp.net VB oauth2.0 call keeps getting cancelled

<pre>
Protected Async Sub BtnGo_Click(sender As Object, e As EventArgs) Handles BtnGo.Click
       Dim Test As String = Await AsyncCall(Nothing)
   End Sub


   Protected Async Function AsyncCall(ByVal e As System.EventArgs) As Task(Of String)

       Dim clientId As String = "4e502cbc-a55f-4341-a498-69cfbe19ee7b"
       Dim clientSecret As String = "my sercret goes here"

       Dim credentials = String.Format("{0}:{1}", clientId, clientSecret)
       Dim headerValue = Convert.ToBase64String(Encoding.UTF8.GetBytes(credentials))

       Dim content = New FormUrlEncodedContent(New Dictionary(Of String, String) From {
                                       {"client_id", clientId},
                                       {"client_secret", clientSecret},
                                       {"grant_type", "client_credentials"},
                                       {"scope", "https://tffproduction.onmicrosoft.com/04cc9749-dbe5-4914-b262-d866b907756b/.default"}
                                       })

       Dim requestMessage = New HttpRequestMessage(HttpMethod.Post, "https://login.microsoftonline.com/ca4f5969-c10f-40d4-8127-e74b691f95de/oauth2/v2.0/token")
       requestMessage.Headers.Authorization = New AuthenticationHeaderValue("Basic", headerValue)
       requestMessage.Content = content

       Dim responsemessage As HttpResponseMessage

       Dim client As New HttpClient

       Try
           responsemessage = Await client.SendAsync(requestMessage)

           If responsemessage.IsSuccessStatusCode Then
               Dim responseContent As String = Await responsemessage.Content.ReadAsStringAsync()

               Return responseContent
           Else

               Return "Error: " & responsemessage.StatusCode.ToString()
           End If
       Catch ex As Exception

           Return "Error: " & ex.Message
       End Try

   End Function