Let django use the x-original-host header to setup absolute urls

Question

Context

We have a Docker container running Django on Azure. The container is served through a Azure Application Gateway.

Because Django is behind a a proxy you should use use the USE_X_FORWARDED_HOST setting to let Django fetch the hostname from that header. See this link for the documentation:

https://docs.djangoproject.com/en/3.0/ref/settings/#std:setting-USE_X_FORWARDED_HOST

Unfortunartly the Azure Application Gateway cannot provide the X-Forwarded-Host header, it does however provide a X-Original-Host.

Source: https://learn.microsoft.com/en-us/azure/application-gateway/how-application-gateway-works#modifications-to-the-request

According to this medium the X-Forwarded-Host header must be set at the public internet facing proxy. So I can not set it on the Nginx proxy running inside the docker container. I have tried with the settings below on Nginx, i see the X-Forwarded-Host is set but it doesn't get picked up by Django.

location / {
        add_header 'Access-Control-Allow-Origin' '*';
        add_header 'Access-Control-Allow-Headers' 'authorization, content-type';
        add_header 'X-Forwarded-Host' 'www.mydomain.com';
        proxy_set_header Host $host;
        proxy_redirect off;
        proxy_pass http://backend_api$request_uri;
    }

And also tried with proxy_set_header X-Forwarded-Host www.mydomain.com. I see the header is set in the response, but Django doesn't use it for the absolute urls.

Question

How can i let django use the X-Orignal-Host instead of the X-Forwarded-Host header? or hardcode the hostname in another way? Preferably I do not want to use the django.contrib.sites module, because it is build for multisite content management.

You could configure your HA proxy in front of django to transform your headers and set `X-Forwarded-Host` according to `X-Original-Host`. — nima, Jan 27 '20 at 13:23
I have tried. I see the header come up in the response, but Django doesn't use it. The nginx is not public and already behind the Application Gateway. So I think thats why it doesn't work, not 100% sure why not. See the medium article I shared. — Florian, Jan 27 '20 at 14:50

score 2 · Accepted Answer · answered Jan 30 '20 at 11:36

I have solved my problem by writing custom middleware that copies the X_Original_Host to X_Forwarded_Host.

Add a file middleware.py with this content:

class MultipleProxyMiddleware:
    FORWARDED_FOR_FIELDS = [
        'HTTP_X_FORWARDED_FOR',
        'HTTP_X_FORWARDED_HOST',
        'HTTP_X_FORWARDED_SERVER',
    ]

    def __init__(self, get_response):
        self.get_response = get_response

    def __call__(self, request):
        """
        Rewrites the proxy headers so that only the most
        recent proxy is used.
        """
        for field in self.FORWARDED_FOR_FIELDS:
            if field in request.META:
                if ',' in request.META[field]:
                    parts = request.META[field].split(',')
                    request.META[field] = parts[-1].strip()

        """
        Rewrites the X Original Host to X Forwarded Host header
        """
        if 'HTTP_X_ORIGINAL_HOST' in request.META:
            request.META['HTTP_X_FORWARDED_HOST'] = request.META['HTTP_X_ORIGINAL_HOST']

        return self.get_response(request)

And add it to your MIDDLEWARE settings:

MIDDLEWARE = [
    'wally.middleware.MultipleProxyMiddleware',
    'corsheaders.middleware.CorsMiddleware',
    'django.middleware.security.SecurityMiddleware',
    'django.contrib.sessions.middleware.SessionMiddleware',
    ....
]

Let django use the x-original-host header to setup absolute urls

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1 Answers1