I get NpgsqlException(0x80004005) when I use MS DTC
<p>I get NpgsqlException(0x80004005) when I use MS DTC.</p>

<p>Npgsql.NpgsqlException (0x80004005): No password has been provided but the backend requires one (in MD5)</p>

<p>Here is an example of the code.</p>

<pre><code>string strcon1 = "Server=localhost;Port=5432;User Id=postgres; Password=xxxxx; Database=db1;enlist=true;";
string strcon2 = "Server=localhost;Port=5432;User Id=postgres; Password=xxxxx; Database=db2;enlist=true;";

using (TransactionScope tx = new TransactionScope())
{
    using (NpgsqlConnection conn1 = new NpgsqlConnection(strcon1))
    {
        string sql = "insert into test1(col1) values('A')";
        conn1.Open();
        using (NpgsqlCommand command = new NpgsqlCommand(sql, conn1))
        {
            command.ExecuteNonQuery();
        }
        using (NpgsqlConnection conn2 = new NpgsqlConnection(strcon2))
        {
            conn2.Open();
            using (NpgsqlCommand command = new NpgsqlCommand(sql, conn2))
            {
                command.ExecuteNonQuery();
            }
        }
    }
    tx.Complete();
} //  Error: tx.Dispose()

Server stack trace: 
Npgsql.NpgsqlConnector.ProcessAuthenticationMessage(String username, AuthenticationRequestMessage msg)
Npgsql.NpgsqlConnector.HandleAuthentication(String username, NpgsqlTimeout timeout)
Npgsql.NpgsqlConnector.Open(NpgsqlTimeout timeout)
Npgsql.ConnectorPool.Allocate(NpgsqlConnection conn, NpgsqlTimeout timeout)
Npgsql.NpgsqlConnection.OpenInternal()
Npgsql.NpgsqlTransactionCallbacks.GetConnection()
Npgsql.NpgsqlTransactionCallbacks.PrepareTransaction()
System.Runtime.Remoting.Messaging.StackBuilderSink._PrivateProcessMessage(IntPtr md, Object[] args, Object server, Object[]&amp;amp;amp; outArgs)
System.Runtime.Remoting.Messaging.StackBuilderSink.SyncProcessMessage(IMessage msg)

Exception rethrown at [0]: 
System.Runtime.Remoting.Proxies.RealProxy.HandleReturnMessage(IMessage reqMsg, IMessage retMsg)
System.Runtime.Remoting.Proxies.RealProxy.PrivateInvoke(MessageData&amp;amp;amp; msgData, Int32 type)
Npgsql.INpgsqlTransactionCallbacks.PrepareTransaction()
Npgsql.NpgsqlResourceManager.DurableResourceManager.Prepare(PreparingEnlistment preparingEnlistment)
System.Transactions.Oletx.OletxEnlistment.PrepareRequest(Boolean singlePhase, Byte[] prepareInfo)
System.Transactions.Oletx.OletxTransactionManager.ShimNotificationCallback(Object state, Boolean timeout)
System.Threading._ThreadPoolWaitOrTimerCallback.PerformWaitOrTimerCallback(Object state, Boolean timedOut)&lt;/StackTrace&gt;&lt;ExceptionString&gt;Npgsql.NpgsqlException (0x80004005): No password has been provided but the backend requires one (in MD5)

Server stack trace: 
Npgsql.NpgsqlConnector.ProcessAuthenticationMessage(String username, AuthenticationRequestMessage msg)
Npgsql.NpgsqlConnector.HandleAuthentication(String username, NpgsqlTimeout timeout)
Npgsql.NpgsqlConnector.Open(NpgsqlTimeout timeout)
Npgsql.ConnectorPool.Allocate(NpgsqlConnection conn, NpgsqlTimeout timeout)
Npgsql.NpgsqlConnection.OpenInternal()
Npgsql.NpgsqlTransactionCallbacks.GetConnection()
Npgsql.NpgsqlTransactionCallbacks.PrepareTransaction()
System.Runtime.Remoting.Messaging.StackBuilderSink._PrivateProcessMessage(IntPtr md, Object[] args, Object server, Object[]&amp;amp;amp; outArgs)
System.Runtime.Remoting.Messaging.StackBuilderSink.SyncProcessMessage(IMessage msg)

Exception rethrown at [0]: 
System.Runtime.Remoting.Proxies.RealProxy.HandleReturnMessage(IMessage reqMsg, IMessage retMsg)
System.Runtime.Remoting.Proxies.RealProxy.PrivateInvoke(MessageData&amp;amp;amp; msgData, Int32 type)
Npgsql.INpgsqlTransactionCallbacks.PrepareTransaction()
Npgsql.NpgsqlResourceManager.DurableResourceManager.Prepare(PreparingEnlistment preparingEnlistment)
System.Transactions.Oletx.OletxEnlistment.PrepareRequest(Boolean singlePhase, Byte[] prepareInfo)
System.Transactions.Oletx.OletxTransactionManager.ShimNotificationCallback(Object state, Boolean timeout)
System.Threading._ThreadPoolWaitOrTimerCallback.PerformWaitOrTimerCallback(Object state, Boolean timedOut)
</code></pre>

<p>Windows Server 2012 R2 standard, 
PostgreSQL 9.6,
Npgsql 3.1.8</p>

<p>How can I solve it?</p>