Get user token in SSO environment

I am working on creating an addon for a 3rd party app, which will show enrolled courses, and their assignments etc. to the user from a portal web app. With a wstoken for a moodle user with the appropriate permissions, I can get course enrollments, and basic course assignment info. (using REST, but not sure that matters)

However, to show more details on the assignments (due dates, submission status, etc.), it appears I need the users' personal token, gotten with /login/token.php

Here is the problem: we are in a SSO environment, where our moodle system(s) do not have the password; they trust the SSO authority.

Is there another way to retrieve the user token?

Thanks,

Johan