Added log to show which URL is blocked by CORS. (#26347)

---------

Co-authored-by: Mattermost Build <build@mattermost.com>

server/channels/api4/websocket.go

@@ -32,7 +32,10 @@ func connectWebSocket(c *Context, w http.ResponseWriter, r *http.Request) {
 
 	ws, err := upgrader.Upgrade(w, r, nil)
 	if err != nil {
-		c.Err = model.NewAppError("connect", "api.web_socket.connect.upgrade.app_error", nil, err.Error(), http.StatusBadRequest)
+		params := map[string]any{
+			"BlockedOrigin": r.Header.Get("Origin"),
+		}
+		c.Err = model.NewAppError("connect", "api.web_socket.connect.upgrade.app_error", params, err.Error(), http.StatusBadRequest)
 		return
 	}
 

server/channels/api4/websocket_test.go

@@ -465,5 +465,5 @@ func TestWebSocketUpgrade(t *testing.T) {
 	require.NoError(t, err)
 	require.Equal(t, resp.StatusCode, http.StatusBadRequest)
 	require.NoError(t, th.TestLogger.Flush())
-	testlib.AssertLog(t, buffer, mlog.LvlDebug.Name, "Failed to upgrade websocket connection.")
+	testlib.AssertLog(t, buffer, mlog.LvlDebug.Name, "URL Blocked because of CORS. Url: ")
 }