minor #4052 [Security] [Custom Provider] Use properties on WebserviceUser (entering)

This PR was submitted for the 2.5 branch but it was merged into the 2.3 branch instead (closes #4052).

Discussion
----------

[Security] [Custom Provider] Use properties on WebserviceUser

Commits
-------

c6ede6d Security] [Custom Provider] Use properties on WebserviceUser
8d69fc8 [Security] [Custom Provider] Use getters on WebserviceUser

Author: weaverryan

cookbook/security/custom_provider.rst

@@ -90,7 +90,7 @@ This is how your ``WebserviceUser`` class looks in action::
                 return false;
             }
 
-            if ($this->getSalt() !== $user->getSalt()) {
+            if ($this->salt !== $user->getSalt()) {
                 return false;
             }