I have been able to activate the Google sign in, however there are a few problems.
When I log in myself, (administrator), through Gibbon login or Google I can view my timetable and also all the classes fine with no problems.
However, when other teachers login through Google, they do not see their classes or any classes in the markbook for example, It is all empty. Even if they have a secondary administrator role, and choose that, still there are no classes visible. The email addresses are definitely the same as the ones in the user database. This problem is not apparent when logging in the traditional way.
2. The log in with Google button is invisible (but works), the image does not show for some reason. I could not work my way around it, I can access the image, if I directly enter the url for the Google sign in logo, which is in the default/img folder. This is not a major problem, but can cause some confusion.
What version of Gibbon are you using and what server are you running it on? I recently worked with Ross to update the login with Google code.
I suspect there is either a problem with caching or a problem with the depreciation of Google APIs that the code pre Gibbon V11 was using.
There is a remote possibility that it could be connected with setting of Base URL and Base Path but I am not sure if this could be causing the issue you are describing. Could you check that the Base Url and Base Path in system settings under the menu Admin > System Admin match your site url. I found that on a Mac Server that there were problems if the case was incorrectly entered eg. http://www.MyGibbonSite/Gibbon instead of http://www.mygibbonsite/gibbon.