Check out the documentation for PMDF API and SIMS API. The MTA comes from PMDF. I just did a quick check and could not find out when documentation will be out regarding iMS-MTA API.
For what you want to accomplish I don't think the MTA-API is where you need to be looking. I know that ME and iDA SSO can be enabled, and I think it can be done with Portal as well, but I do not know how.