[web-annotation] Client can't determine if user has authorization to modify annotation

azaroth42 has just created a new issue for 
https://github.com/w3c/web-annotation:

== Client can't determine if user has authorization to modify 
annotation ==
Clients typically display whether the current user can modify an 
annotation when presenting them to the user.  The client might wish to
 present an edit button only when the edit is possible, rather than 
for every annotation on the chance that the user can edit it. 

Currently there's nowhere in the model where this information can be 
conveyed.

See https://github.com/w3c/web-annotation/issues/19