we are trying to enable the One Tap sign-up from Google. It seems there was some security concern (reading online not officially by google) and the official document has been taken out by Google.
Is that API still working, can we integrate it or should we wait for it?
You can find related functionality in Smart Lock for Passwords section here
Looks like original SDK was removed in favor of more common browser Credentials Management API (draft of w3c) in Сhrome 51 and then reworked in Chrome 60.
Also, they have a codelabs tutorial to learn it step by step.