How to copy X-Forwarded-For header to another header variable in AFD Standard rule set?

Question

How to copy X-Forwarded-For header to another header variable in AFD Standard rule set?

takeolexus 200

Hello,

I am trying to add a rule set in AFD Standard to copy the X-Forwarded-For header to a different header variable.

The reason is that when configuring the Forwarded Headers Middleware in the backend ASP.NET Core, I need to dynamically obtain and set all of the AFD backend IP address using options.KnownProxies.Add(IPAddress.Parse("xxx.xxx.xxx.xxx")). To avoid this, I want to copy the X-Forwarded-For header to another header variable so that the Forwarded Headers Middleware does not interfere with retrieving the X-Forwarded-For header.

I defined the rule and associated it with the route as shown below, but the variable could not be retrieved.

Header Value is '{http_req_header_X-Forwarded-For}'. User's image

I referred to the following Learn article:

https://learn.microsoft.com/en-us/azure/frontdoor/rules-engine-scenarios?tabs=portal#scenario-2-populate-or-modify-a-response-header-based-on-a-request-header-value

Is it not possible to copy the X-Forwarded-For header to another header variable using this method?

Thank you in advance.

takeolexus 200 Reputation points

2025-07-31T23:36:25.5233333+00:00

Hello @Praveen Bandaru

Thank you for your response.

For example, when the header value is a static value like 'TEST' instead of '{http_req_header_X-Forwarded-For}', it can be retrieved correctly on the backend ASP.NET Core.

Therefore, I think the issue is either with how this server variable is being used or that the 'X-Forwarded-For' header cannot be obtained at all.
Praveen Bandaru 6,850 Reputation points Microsoft External Staff Moderator

2025-08-01T09:35:10.8633333+00:00

Hello takeolexus
Thank you for your response. Could you please confirm if the backend application will support access using an X-forwarded header. If it does, please set up a rule with the appropriate server variable.

Hope the above answer helps! Please let us know do you have any further queries.

Please do not forget to “up-vote” wherever the information provided helps you, this can be beneficial to other community members.
Praveen Bandaru 6,850 Reputation points Microsoft External Staff Moderator

2025-08-04T02:21:22.45+00:00

Hello takeolexus

I just wanted to follow up and see if you had a chance to review my response to your question. Please let us know if it was helpful, and feel free to reach out if you have any further queries.

Hope the above answer helps! Please let us know do you have any further queries.

Please do not forget to "accept answer" and “up-vote” wherever the information provided helps you, this can be beneficial to other community members.

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takeolexus 200 Reputation points

2025-07-31T23:36:25.5233333+00:00

Hello @Praveen Bandaru

Thank you for your response.

For example, when the header value is a static value like 'TEST' instead of '{http_req_header_X-Forwarded-For}', it can be retrieved correctly on the backend ASP.NET Core.

Therefore, I think the issue is either with how this server variable is being used or that the 'X-Forwarded-For' header cannot be obtained at all.
Praveen Bandaru 6,850 Reputation points Microsoft External Staff Moderator

2025-08-01T09:35:10.8633333+00:00

Hello takeolexus
Thank you for your response. Could you please confirm if the backend application will support access using an X-forwarded header. If it does, please set up a rule with the appropriate server variable.

Hope the above answer helps! Please let us know do you have any further queries.

Please do not forget to “up-vote” wherever the information provided helps you, this can be beneficial to other community members.
Praveen Bandaru 6,850 Reputation points Microsoft External Staff Moderator

2025-08-04T02:21:22.45+00:00

Hello takeolexus

I just wanted to follow up and see if you had a chance to review my response to your question. Please let us know if it was helpful, and feel free to reach out if you have any further queries.

Hope the above answer helps! Please let us know do you have any further queries.

Please do not forget to "accept answer" and “up-vote” wherever the information provided helps you, this can be beneficial to other community members.

Answer 1

Hello takeolexus
You're attempting to copy the X-Forwarded-For header to a different header variable in Azure Front Door (AFD) so your backend ASP.NET Core application can access it correctly without any issues.You should make sure that you're using the Rules Engine properly to modify the header as needed. According to the documentation on header actions in AFD, you can set up a rule to change the request headers.
Here we need to add ruleset for the route that is matching incoming request custom domain and path users are accessing. You can set the new header to the value of X-Forwarded-For by using the header modification action type:

For example, assign the header value as {http_req_header_X-Forwarded-For}.

Please ensure that the changes are deployed and properly linked to the route you are working on.

If you’ve already configured this and it isn’t working, try the following checks:

Make sure the rule is enabled and properly linked to the AFD route.
Verify that no other rules or settings are conflicting and affecting header processing.

Please check the below reference document:

https://learn.microsoft.com/en-us/azure/frontdoor/front-door-http-headers-protocol

Hope the above answer helps! Please let us know do you have any further queries.

Please do not forget to “up-vote” wherever the information provided helps you, this can be beneficial to other community members.

takeolexus 200 Reputation points

2025-08-04T02:50:08.01+00:00

AFD seems unable to copy the X-Forwarded-For header regardless of the backend. Thank you very much.

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How to copy X-Forwarded-For header to another header variable in AFD Standard rule set?

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