We are developing a hybrid mobile app (code is written in HTML and runs on browser shell as a native app on the device). We need to authenticate the user against an external security manager. I've seen the Gmail App in iPhone which opens a browser to authenticate the user. We are also looking to do something of that sort. We just need to gather your thoughts on how authentication can be done with some external security manager in a mobile app.
Also I noticed that Dailymotion website was able to know if the user is authenticated with Facebook. This looks like a cross domain authentication.
Can you please share your thoughts on how Google and others have implemented it?
What you are looking for is OAuth and OpenID services to federate your login. Depending on the architecture of your system you can implement whichever one you like or even a hybrid of both.
Take a look at this link: Federated Login for Google Accounts
It provides all the useful information you need.