ident: don't expose register page if it doesn't exist for method (#40935)

tests/test_fc_auth.py

@@ -350,3 +350,10 @@ def test_fc_logout_error():
     setup_fc_environment(pub)
     app = get_app(pub)
     app.get('/ident/fc/logout', status=400)
+
+
+def test_fc_register_error():
+    setup_user_profile(pub)
+    setup_fc_environment(pub)
+    app = get_app(pub)
+    app.get('/register/fc/', status=404)

wcs/root.py

@@ -182,6 +182,8 @@ class RegisterDirectory(Directory):
     def _q_lookup(self, component):
         try:
             dir = ident.get_method_directory(component)
+            if 'register' not in dir._q_exports:
+                return errors.TraversalError()
             # set the register page as the index page, so the url can be
             # /register/password/ instead of /register/password/register
             dir._q_exports.append('')