BUG #15161: libpq - Invalid SSPI context after PQreset

The following bug has been logged on the website:

Bug reference: 15161
Logged by: Petrovan Bogdan
Email address: petrovanster(at)gmail(dot)com
PostgreSQL version: 9.3.5
Operating system: Windows Server 7 and 2012R2
Description:

When doing multiple parallel connects/resets I'm getting two types of
errors:

2018-04-17 00:00:21 EEST FATAL: invalid frontend message type 112

2018-04-17 00:28:21 EEST FATAL: could not accept SSPI security context
2018-04-17 00:28:21 EEST DETAIL: The token supplied to the function is
invalid

Originally this happens on a php backend. I've went "downstream" from the
php adodb library, to php_psql and then to libpq, which is the underlying
client library.

php_psql extension does a PQreset on the connection resource.

I was able to reproduce the issue with a small C++ app:

#include "stdafx.h"
#include <libpq-fe.h>
#include <thread>

#include <iostream>

using namespace std;

void test()
{
for (int i = 0; i < 10; i++)
{
PGconn* conn = PQconnectdb("hostaddr=127.0.0.1 port=5432 host=***
user=user1 dbname=db");
auto status = PQstatus(conn);

if (status == CONNECTION_BAD)
{
cout << "connection bad after connect" << endl;
}
PQfinish(conn);
}
}

int main()
{
const int N = 100;
thread threads[N];
for (int i = 0; i < N; i++)
{
threads[i] = thread(test);
}
for (int i = 0; i < N; i++) {
threads[i].join();
}
return 0;
}

When running the application on the same machine as the postgres service, I
get the "could not accept SSPI security context" error.

SSPI authentication host is the local computer, not an AD.

I've tried also changing the application to run a single thread and start 10
instances of it. In this case there is no sspi error. Thus I suspect the
libpq implementation.

Using the application above there is no "invalid frontend message type 112".
But when I add a PQreset before PQfinish (like php_pgsql ext does), it will
appear.