How to solve CORS problem of my Django API?

Question

I cannot solve CORS problem in my Django API. When I make a call to this API, I get error:

Access to fetch at 'http://localhost:8000/' from origin 'http://localhost' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource. If an opaque response serves your needs, set the request's mode to 'no-cors' to fetch the resource with CORS disabled.

To enable CORS, I did pip install django-cors-headers and added the following code to settings.py:

INSTALLED_APPS = [
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
    'corsheaders',
]

MIDDLEWARE_CLASSES = [
    'corsheaders.middleware.CorsMiddleware',
    'django.middleware.common.CommonMiddleware',
    'django.middleware.security.SecurityMiddleware',
    'django.contrib.sessions.middleware.SessionMiddleware',
    'django.middleware.common.CommonMiddleware',
    'django.middleware.csrf.CsrfViewMiddleware',
    'django.contrib.auth.middleware.AuthenticationMiddleware',
    'django.contrib.auth.middleware.SessionAuthenticationMiddleware',
    'django.contrib.messages.middleware.MessageMiddleware',
    'django.middleware.clickjacking.XFrameOptionsMiddleware',
]

CORS_ORIGIN_WHITELIST = [
    'localhost:80',
    'localhost:8000',
    '127.0.0.1:8000'
]

I should say that I run my project on Docker. This is docker-compose.yml:

version: '2'

services:
  django-docker:
    build:
      context: .
      dockerfile: Dockerfile.django
    container_name: my.django
    image: my-django
    ports:
      - 8000:8000

  webapp-docker:
    build:
      context: .
      dockerfile: Dockerfile.webapp
    container_name: my.webapp
    image: my-web
    ports:
      - 80:80

Answer 1

You need to add corsheaders.middleware.CorsMiddleware middleware to the middleware classes in settings.py :

MIDDLEWARE_CLASSES = (
    'corsheaders.middleware.CorsMiddleware',
    'django.middleware.common.BrokenLinkEmailsMiddleware',
    'django.middleware.common.CommonMiddleware',
    #...
)

You have duplicate django.middleware.common.CommonMiddleware in your middleware classes.

You can then, either enable CORS for all domains by adding the following setting:

CORS_ORIGIN_ALLOW_ALL = True

Or Only enable CORS for specified domains:

CORS_ORIGIN_ALLOW_ALL = False

CORS_ORIGIN_WHITELIST = (
    'http//:localhost:8000',
)

Answer 2

Try to add this in your settings:

from corsheaders.defaults import default_headers

CORS_ALLOW_HEADERS = default_headers + (
    'Access-Control-Allow-Origin',
)