by Joscha Zander.
*Update for my initial question:
I was able to send grades back to moodle with (org.imsglobal.pox.IMSPOXRequest)
IMSPOXRequest.sendReplaceResult(request.getParameter("lis_outcome_service_url"), request.getParameter("oauth_consumer_key"), getSecret(), request.getParameter("lis_result_sourcedid"),"1");
This call will set my own grade to 100% in moodle (i am the testing user).
In the end it was very easy to send the grades back. However i study computer science and from a developers perspective the documentations (for any LTI package i have found so far) is superrr horrible. I can not imagine how it must be for a teacher...
If requested by anyone - I will speak to my supervisor to publish my solution in the end.
best regards
Joscha Zander