Intermittent SQL Login Issues in Windows Server 2016 with Azure AD Token

Question

I am running into intermittent login issue to an Azure SQL Database specifically from a Windows Server 2016 machine. I have an application that continuously, every 30 seconds, requests an Azure AD Token and uses that token in the sql connection object to connect to SQL Server and run a query. This loop intermittently fails with a login failed for user NT AUTHORITY\ANONYMOUS LOGON.

The failure seems to follow a pattern in which it works for 6 requests, then fails for 6 requests. I also changed the loop time to 15 seconds and the pattern doubled.

I ran the same console application on two different Windows 10 machines and a Windows Server 2012 R2 and it worked with no issues.

The code for the application is as follows (the variables to retrieve the token are not shown for security reasons):

while (true)
            {
                var token = Task.Run(() => 
 SignInWithClientSecret("https://database.windows.net/", aadinstance, 
 applicationId, secret, true)).Result;
                using (SqlConnection conn = new 
 SqlConnection(connectionstring))
                {
                    conn.AccessToken = token.AccessToken;
                    //Console.WriteLine(token.AccessToken);
                    try
                    {
                        conn.Open();
                        using (var cmd = new SqlCommand(sqlcommand, conn))
                        {
                            var result = cmd.ExecuteNonQuery();
                            Console.WriteLine("Executed command");
                        }
                    }
                    catch (Exception ex)
                    {
                        Console.WriteLine("Error executing sql command: " + 
 ex.Message);
                    }
                }
                Thread.Sleep(30000);
            }

Answer 1

The issue was due to the .NET Framework installed. I upgraded to 4.7.2 and it works.