For those of you who are here in hopes of getting some clarity on the outdated solution in step 5 of Lesson 6: Create Google Sign in here is some helpful documentation that shows more up to date implementation of what is needed in the login.html file.
server-side-flow
Following through step 6 should provide insight into what is new to the Google OAuth2 functionality. Step 7 would replace what is already provided as a solution in the project.py file for the /gconnect endpoint, if that is something of interest.
Hopefully Udacity can make updates to this repo and the course videos soon...