-  user_property(+Identity, ?Property) is nondet
 - True when Identity has Property. Defined properties are:
- peer(Atom)
 - Remote IP address
 
- identity(Atom)
 - Identity as provided by some identity provider
 
- identity_provider(Atom)
 - Subsystem that identified the user
 
- external_identity(Atom)
 - Identity as provided by the identity_provider
 
- profile_id(Atom)
 - Identifier of the profile we have on this user.
 
- login(Atom)
 - Same as 
identity_provider(Atom) 
- name(Atom)
 - Name associated with the identity
 
- email(Atom)
 - Email associated with the identity