SkyPrep also allows single-sign on using the API.
You can make an API call to /get_login_key with the corresponding user information, and the API will return a link that you can use to log-in the user.
The general flow is:
Your app ➝ Request to SkyPrep API ➝ returns Link ➝ embed in website ➝ user clicks/follows redirect
The SSO API call has a few options. You can either use daily login links (which work for the entire day, UTC time), time expiring links (so the link expires at a certain date/time) or one time use links (that expire as soon as they are used).