We're started experiencing the same issue 20 hours ago, but it's appearing on both production and localhost (which use two separate Google accounts). The strange thing is that we are able to log in every 3 or 4 tries, but not every time.
As far as an API change on Google's end, this issue on omniauth-google-oauth2 seems relevant: https://github.com/zquestz/omniauth-google-oauth2/issues/106. However, this deprecation should not be enforced until September, 2014.
Also, editing the omniauth-google-oauth2 gem directly and changing these lines:
class GoogleOauth2 < OmniAuth::Strategies::OAuth2
BASE_SCOPE_URL = "https://www.googleapis.com/auth/"
DEFAULT_SCOPE = "userinfo.email,userinfo.profile"
to this:
class GoogleOauth2 < OmniAuth::Strategies::OAuth2
BASE_SCOPE_URL = "https://www.googleapis.com/auth/"
DEFAULT_SCOPE = "email,profile"
Yielded this error:
Error: invalid_scope Some requested scopes were invalid. {invalid=[https://www.googleapis.com/auth/profile, https://www.googleapis.com/auth/email]}
Update: Quoted from an email from Lever (hire.lever.co):
"The issue stemmed from an bug in a release Google made to the authentication system Lever uses to identify users last night. We were among some apps who lost the ability to verify users via their Google OAuth API. We've been in communication with Google, and we've been told that the release was reverted at 11:30AM PDT."
Google OAuth appears to be fixed for us now.