EmID: Web Authentication by Email Address

It suggests that OpenID should use email addresses rather than URLs as identifiers, and show how OpenID can be adapted accordingly with relative ease. Email addresses provide better backwards compatibility with existing web authentication paradigms, map to existing trust decisions more closely, and provide a smoother, less intrusive adoption curve. Of particular interest to privacy advocates, a username-and-domain approach to web identifiers lends itself more naturally to cryptographic authentication protocols where the identity provider need not learn its users' every authentication event.