CORS middleware for Django

gistfile1.py

import re

from django.utils.text import compress_string
from django.utils.cache import patch_vary_headers
from django.conf import settings

from django import http

XS_SHARING_ALLOWED_ORIGINS = getattr(settings, 'XS_SHARING_ALLOWED_ORIGINS', ['*'])

XS_SHARING_ALLOWED_METHODS = getattr(settings, 'XS_SHARING_ALLOWED_METHODS', [
    'POST',
    'GET',
    'OPTIONS',
    'PUT',
    'DELETE'
])


class XsSharing(object):
    """ Allows cross-domain XHR using the html5 postMessage API. """

    def process_request(self, request):
        if 'HTTP_ACCESS_CONTROL_REQUEST_METHOD' in request.META:
            if 'HTTP_ORIGIN' in request.META:
                if request.META['HTTP_ORIGIN'] in XS_SHARING_ALLOWED_ORIGINS or '*' in XS_SHARING_ALLOWED_ORIGINS:
                    response = http.HttpResponse()
                    response['Access-Control-Allow-Origin'] = request.META['HTTP_ORIGIN'] 
                    response['Access-Control-Allow-Methods'] = ",".join(XS_SHARING_ALLOWED_METHODS) 
                    return response

        return None

    def process_response(self, request, response):
        if response.has_header('Access-Control-Allow-origin'):
            return response

        if 'HTTP_ORIGIN' in request.META:
            if request.META['HTTP_ORIGIN'] in XS_SHARING_ALLOWED_ORIGINS or '*' in XS_SHARING_ALLOWED_ORIGINS:
                response['Access-Control-Allow-Origin'] = request.META['HTTP_ORIGIN'] 
                response['Access-Control-Allow-Methods'] = ",".join(XS_SHARING_ALLOWED_METHODS) 

        return response

~                                                                                                                                          

The "Access-Control-Allow-Headers" header is not set during a preflight OPTIONS request.
The snippet below can be added between line 28 and 29 to fix that. Sure, it can be configured via the settings file
as well like you already have for the other two headers.
response['Access-Control-Allow-Headers'] = request.META['HTTP_ACCESS_CONTROL_REQUEST_HEADERS']