Possible Duplicate:
Google login in my site
I have an php website with login form and I want every visitors can able to login into my website using their gmail account???
Possible Duplicate:
Google login in my site
I have an php website with login form and I want every visitors can able to login into my website using their gmail account???
You need to look at OpenID, it will let users choose a variety of common login sources
See here for additional detail regarding implementation:
OAuth could let you use the gmail services, once the user gives you the authorization to do it