I have used Google with the SAML module succesfully. I created an SSO app in the Google Admin console pointing to a Mendix app. Once the Google SSO App parameters were complete, I donwloaded a file from Google with the info and uploaded it into the Mendix App via the SSO admin pages. Not sure if this has been corrected in newer releases of the SAML module, but I discovered that you have to use the Name attribute in Mendix as the UserID identifier. I tried using Email attribute and it didn't work. When I put email addresses in the Name attribute and then used that for SSO, it worked.
If it helps, here is a screen shot of the Google SSO app parameters page:
Hope that helps,