Having spoken to the product manager at google, I got the following response:
While there is no service level agreement (SLA) for the Google Identity Toolkit, Google itself uses the same infrastructure as GITKit to support federated login for Google accounts. Google users can even opt-in to use an Account Chooser in place of the traditional Google login box.
Sorry for the delayed reply. When I mentioned T&Cs I meant the risk that the provider you use changes the terms and conditions some time after you've deployed and have an established user base that relies on the provider's service.
While there is no service level agreement (SLA) for the Google Identity Toolkit, Google itself uses the same infrastructure as GITKit to support federated login for Google accounts. Google users can even opt-in to use an Account Chooser in place of the traditional Google login box.
https://code.google.com/apis/identitytoolkit/v1/learnmore.ht...