Allow for PKCE oauth2 grant flow method

Author: nirvn

src/core/qfieldcloudconnection.cpp

@@ -587,7 +587,7 @@ void QFieldCloudConnection::setAuthenticationToken( QNetworkRequest &request )
       configMap["configType"] = 1;
       configMap["description"] = QString( "Connection details for QFieldCloud using %1 provider" ).arg( mProvider );
       configMap["extraTokens"] = providerDetails.value( "extra_tokens" ).toMap();
-      configMap["grantFlow"] = 0;
+      configMap["grantFlow"] = providerDetails.value( "grant_flow" ).toInt();
       configMap["name"] = QString( "Autogenerated by QField" );
       configMap["persistToken"] = true;
       configMap["redirectHost"] = QString( "localhost" );