The login is done via HTTP Basic Authentication with the exception that you'll provide "SSO" instead of "Basic" in the Authorization header.
Provide the following:
• Username - the E-Mail Address of the Passcreator account that should be logged in
• Password - the SSO Token that you have requested
If the login has been successful HTTP Status 200 is returned which means that you can now redirect your user to the Passcreator application.