public class BroadleafSocialSignInAdapter
The SignInAdapter is exclusively used for provider sign in so a SignInAdapter
bean will need to be added to the Spring Social configuration.
The signIn() method takes the local application user's user ID normalized as a String.
No other credentials are necessary here because by the time this method is called the user will have signed
into the provider and their connection with that provider has been used to prove the user's identity.
This adapter will then authenticate manually against Spring Security
this will automatically be injected into ProviderSignInController,
as long as this package is scanned
(make sure the following is in applicationContext-servlet.xml)