I see tons of solutions for allowing Google Apps to use external AD and LDAP services for login.
However, I already have a ton of users setup in Google Apps already, and I'm trying to go the other way around. That is, I'd like to allow users to log into my external servers using the accounts I created in Google Apps.
Has anyone successfully discovered a way to use a Google Apps domain as an Open Directory, Active Directory, or LDAP provider?
Best Answer
This is absolutely impossible.
Yes, there are means to synchronize between local directory services and Google's directory, but that doesn't mean that you can use Google's directory like AD, OD, or even a simple LDAP service.
Now, if all you want is to enable users to be able to use their Google credentials to sign into your application, look into OpenID.
Note: See answer 4 years after this answer by trs-80 stating that Google introduced a solution.