Hello SLUser
I do not think it is possible to start a user session in Moodle from RosarioSIS, using web services.
There may be a Moodle plugin which approaches this goal:
https://moodle.org/plugins/?q=single%20sign%20on
The plugin allowing SSO from MediaWiki could be a good start.
If you wish to sponsor the development, please contact us at https://www.rosariosis.org/services/