I'm using latest code from "dotnetopenauth" library downloaded from Git.
I didn't find an example to satisfy OAuth2.0 "Username and Password Flow" basically same case as per this post
EDIT: I guess ExchangeUserCredentialForTokenAsync within DotNetOpenAuth.OAuth2.ClientBase is what I'm looking for: I have been able to get an access token explicitly using Token endopint directly from the client.