Implementation of Tizen SSO APIs

Implementation of SSO APIs as per widl file https://code.google.com/p/accounts-sso/source/browse/widl/signon.widl?repo=libgsignon-glib

Backend that provides core functionality is gSSO and more information about that
component could be found at https://01.org/gsso
`RequestCredentialsUpdateCb()`, `AddReferenceCb()`, `RemoveReferenceCb()`, `RemoveCb()` and `SignoutCb()`

Are they really exactly the same? If so why not just use one function?