An excerpt from insightful Louis Gray analysis. I doubt Apple will succeed as an identity/authentication/authorization service beyond its own properties.
One of the greatest tug of wars amidst leading Web companies today is that for ownership of your identity, through your personal profile, or pushing you to "Sign in with" their credentials. You may sign in with Twitter, Facebook, Google or OpenID, and enable those services to certify it's you. One of the most successful tech companies out there who never comes up in this conversation is Apple, and it's incredible to think how easily they could have converted its army of Mac loyalists (myself included) to "Sign in With Mac", carrying the Apple flag forward as a badge of honor.