Disable linked users in IDP

Author: michielbdejong

lib/models/authenticator.js

@@ -144,7 +144,9 @@ class PasswordAuthenticator extends Authenticator {
           error.statusCode = 400
           throw error
         }
-
+        if (foundUser.link) {
+          throw new Error('Linked users not currently supported, sorry (external WebID without TLS?)')
+        }
         return this.userStore.matchPassword(foundUser, this.password)
       })
       .then(validUser => {