Upload assignment on Moodle using REST webservice function

I am trying to develop a Moodle Android app. I am using MoodleREST source code for my reference. But rest code to upload assignment is not provided by this library. I want to be able to upload assignment from mobile client with a webservice call. Uploading assignment using a webview is possible but in that case user need to login again to access upload assignment page. I have found something similar here https://moodle.org/mod/forum/discuss.php?d=207875. I am new to moodle and still learning it, so my question can be a little naive so please bear with it :)