Init the session. Preserves potential LTI information.

def _set_session(self, username, realname, email, language):
        """ Init the session. Preserves potential LTI information. """
        self._session.loggedin = True
        self._session.email = email
        self._session.username = username
        self._session.realname = realname
        self._session.language = language
        self._session.token = None
        if "lti" not in self._session:
            self._session.lti = None