Fix external auth returns for query_user calls

Adds the missing field on the query_user calls, updates the external auth tests to ensure it is returned properly, and adds new end-to-end tests which call the external auth engines via the *API*, to ensure this doesn't break again

endpoints/api/search.py

@@ -10,6 +10,7 @@ from auth.permissions import (OrganizationMemberPermission, ReadRepositoryPermis
 from auth.auth_context import get_authenticated_user
 from auth import scopes
 from app import avatar, authentication
+from flask import abort
 from operator import itemgetter
 from stringscore import liquidmetal
 from util.names import parse_robot_username
@@ -17,13 +18,15 @@ from util.names import parse_robot_username
 import anunidecode # Don't listen to pylint's lies. This import is required.
 import math
 
-@show_if(authentication.federated_service) # Only enabled for non-DB auth.
 @resource('/v1/entities/link/<username>')
 @internal_only
 class LinkExternalEntity(ApiResource):
   """ Resource for linking external entities to internal users. """
   @nickname('linkExternalUser')
   def post(self, username):
+    if not authentication.federated_service:
+      abort(404)
+
     # Only allowed if there is a logged in user.
     if not get_authenticated_user():
       raise Unauthorized()