I see you have directions for SSO which would require some work from an IT dept, but is there just a simple one that has them enter in a code emailed to them?
You may want to explore SurveyGizmo’s Login/Password Action:
The feature allows you to upload a list of usernames/passwords and requires that a password be entered before a survey response can be initiated.
There is also some documentation on including your passwords within email invitations:
Hope this helps!