Flutter Django应用程序托管在Netlify和Heroku上。当用户尝试登录时，显示以下错误消息：Access to XMLHttpRequest at [heroku url] from origin [netlify url] has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.在Django设置中，我有以下内容：

#settings.py

INSTALLED_APPS = [
    # other apps
    'corsheaders',
]

MIDDLEWARE = [
    'corsheaders.middleware.CorsMiddleware',
    # other middlewares
]

CORS_ORIGIN_ALLOW_ALL = False

CORS_ORIGIN_WHITELIST = [
    [netlify url],
    [heroku url],

]

在netlify上，我做了以下补充：_headers和.toml，并在build命令中添加了_headers：

Build Command: 
if [ -d "flutter" ]; then cd flutter && git pull && cd ..; else git clone https://github.com/flutter/flutter.git; fi; flutter/bin/flutter build web; cp _headers build/web/

#_headers
/*
  Access-Control-Allow-Origin: *

#netlify.toml
[[headers]]
  for = "/*"  # Match all paths
  [headers.values]
    Access-Control-Allow-Origin = "*"  # or specify your allowed domains here
    Access-Control-Allow-Headers = "Origin, X-Requested-With, Content-Type, Accept"
    Access-Control-Allow-Methods = "GET, POST, PUT, DELETE, OPTIONS"

我已经联系了Netlify支持，他们说：“据我所知，无论您连接到什么API，都不会发送该响应：
没有访问控制头。由于Netlify不提供此服务（如您所见，服务器是gunicorn），因此我们无法帮助您。
我有一个heroku配置vars，其中的ALLOWED_HOSTS设置为允许访问netlify。我不知道我还能做什么来解决这个问题。任何想法？任何帮助是非常感谢！