Patching an Online DirectQuery datasource

Hi,

I can execute a patch request to set the credentials of a online directquery datasource using the HttpClient class with no problem. But now I'm looking for a way to do this using the classes of the Microsoft.PowerBI.Api NuGet Package but I cannot find what method to use. I did find a class named GatewayDatasource which looks like the json payload for a patch. But that is as far as I've come... 

Thanks

Gunter