Fix HTTP Basic Auth popups caused by auth failures.

If a user's session cookie expired, the next REST API request their
browser did would go into the json_unauthorized code path.  This
returned a response with a WWW-Authenticate tag for HTTP Basic Auth
(since that's what the REST API uses), even for /json requests which
should only be authenticated using session auth.

We fix this by explicitly passing the desired WWW-Authenticate state.

Fixes: #800.

zerver/lib/response.py

@@ -10,14 +10,19 @@ from six import text_type
 class HttpResponseUnauthorized(HttpResponse):
     status_code = 401
 
-    def __init__(self, realm):
-        # type (text_type) -> None
+    def __init__(self, realm, www_authenticate=None):
+        # type (text_type, Optional[text_type]) -> None
         HttpResponse.__init__(self)
+        if www_authenticate is None:
             self["WWW-Authenticate"] = 'Basic realm="%s"' % (realm,)
+        elif www_authenticate == "session":
+            self["WWW-Authenticate"] = 'Session realm="%s"' % (realm,)
+        else:
+            raise Exception("Invalid www_authenticate value!")
 
-def json_unauthorized(message):
-    # type: (text_type) -> text_type
-    resp = HttpResponseUnauthorized("zulip")
+def json_unauthorized(message, www_authenticate=None):
+    # type: (text_type, Optional[text_type]) -> HttpResponse
+    resp = HttpResponseUnauthorized("zulip", www_authenticate=www_authenticate)
     resp.content = ujson.dumps({"result": "error",
                                 "msg": message}) + "\n"
     return resp

zerver/lib/rest.py

@@ -83,8 +83,11 @@ def rest_dispatch(request, globals_list, **kwargs):
                 # If this looks like a request from a top-level page in a
                 # browser, send the user to the login page
                 return HttpResponseRedirect('%s/?next=%s' % (settings.HOME_NOT_LOGGED_IN, request.path))
-            else:
+            elif request.path.startswith("/api"):
                 return json_unauthorized(_("Not logged in: API authentication or user session required"))
+            else:
+                return json_unauthorized(_("Not logged in: API authentication or user session required"),
+                                         www_authenticate='session')
 
         if request.method not in ["GET", "POST"]:
             # process_as_post needs to be the outer decorator, because