You will be using the OAuth , in which Windows Live, Google, Facebook and Twitter will be the way in which you have options of connecting users.
I needed to get more information on user and thus I wrote a question and ended up using the LoginAsync, but then 2 other things were CRITICAL for me to get more information
var userInfo = await MobileServices.MobileService.InvokeApiAsync(
"userInfo", HttpMethod.Get, null);
Then
with a Custom API - node.js code
THEN an area in the portal with adding "SCOPE" which in Azure portal is like a web.config / app.config , then I was able to get email address (it does warn the user about it sharing this information, which is normal)
Visit this link:
Azure Mobile Services - Getting more user information