Disconnect any leftover connections when destroying auth manager

If one of these connections is triggered after destruction of auth manager, bad things happen because the slot tries to access the mutex which has gone for good along with the auth manager itself.

src/core/auth/qgsauthmanager.cpp

@@ -140,12 +140,14 @@ QSqlDatabase QgsAuthManager::authDatabaseConnection() const
       // triggers a condition in QSqlDatabase which detects the nullptr private thread data and returns an invalid database instead.
       // QSqlDatabase::removeDatabase is thread safe, so this is ok to do.
       // Right about now is a good time to re-evaluate your selected career ;)
-      connect( QThread::currentThread(), &QThread::finished, QThread::currentThread(), [connectionName, this ]
+      QMetaObject::Connection connection = connect( QThread::currentThread(), &QThread::finished, QThread::currentThread(), [connectionName, this ]
       {
         QMutexLocker locker( mMutex );
-        QgsDebugMsgLevel( QStringLiteral( "Removing outdated connection to %1 on thread exit" ).arg( connectionName ), 2 );
         QSqlDatabase::removeDatabase( connectionName );
+        mConnectedThreads.remove( QThread::currentThread() );
       }, Qt::DirectConnection );
+
+      mConnectedThreads.insert( QThread::currentThread(), connection );
     }
   }
   else
@@ -2961,6 +2963,15 @@ void QgsAuthManager::tryToStartDbErase()
 
 QgsAuthManager::~QgsAuthManager()
 {
+  QMutexLocker locker( mMutex );
+  QMapIterator<QThread *, QMetaObject::Connection> iterator( mConnectedThreads );
+  while ( iterator.hasNext() )
+  {
+    iterator.next();
+    iterator.key()->disconnect( iterator.value() );
+  }
+  locker.unlock();
+
   if ( !isDisabled() )
   {
     delete QgsAuthMethodRegistry::instance();

src/core/auth/qgsauthmanager.h

@@ -900,6 +900,8 @@ class CORE_EXPORT QgsAuthManager : public QObject
     //! password helper folder in the wallets
     static const QLatin1String AUTH_PASSWORD_HELPER_FOLDER_NAME;
 
+    mutable QMap<QThread *, QMetaObject::Connection> mConnectedThreads;
+
     friend class QgsApplication;
 
 };