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Request Header Transform Rules

Use Request Header Transform Rules to manipulate the headers of HTTP requests sent to your origin server.

flowchart LR
accTitle: Header modifications diagram
accDescr: Header transform rules can change the headers sent to your origin server (request header modifications) or sent your your website visitors (response header modifications).

A[Visitor]
B((Cloudflare))
C[(Origin server)]

A -.-> B == "Includes request<br> header modifications" ==> C
C -.-> B -. "Includes response<br> header modifications" .-> A

style A stroke-width: 2px
style B stroke: orange,fill: orange,color: black
linkStyle 0,2,3 stroke-width: 1px
linkStyle 1 stroke-width: 3px

To modify HTTP headers in the response sent to website visitors, refer to Response Header Transform Rules.

Through Request Header Transform Rules you can:

  • Set the value of an HTTP request header to a literal string value, overwriting its previous value or adding a new header to the request.
  • Set the value of an HTTP request header according to an expression, overwriting its previous value or adding a new header to the request.
  • Remove an HTTP header from the request.

You can create a request header transform rule in the dashboard, via API, or using Terraform.

For more complex request header modifications, consider using Snippets.

Important remarks

  • You cannot modify or remove HTTP request headers whose name starts with x-cf- or cf- except for the cf-connecting-ip HTTP request header, which you can remove.

  • Due to protocol compliance reasons, modifying or removing request headers with forbidden header names ↗ (such as Accept-Encoding) is generally not allowed in Request Header Transform Rules.

  • You cannot modify the value of any header commonly used to identify the website visitor's IP address, such as x-forwarded-for, true-client-ip, or x-real-ip. Additionally, you cannot remove the x-forwarded-for header.

  • You cannot set or modify the value of cookie HTTP request headers, but you can remove these headers. Configuring a rule that removes the cookie HTTP request header will remove all cookie headers in matching requests.

  • If you modify the value of an existing HTTP request header using an expression that evaluates to an empty string ("") or an undefined value, the HTTP request header is removed.

  • The HTTP request header removal operation will remove all request headers with the provided name.

  • Currently, there is a limited number of HTTP request headers that you cannot modify. Cloudflare may remove restrictions for some of these HTTP request headers when presented with valid use cases. Create a post in the community ↗ for consideration.

  • To use claims inside a JSON Web Token (JWT), you must first set up a token validation configuration in API Shield.

Troubleshooting

When troubleshooting Request Header Transform Rules, use Cloudflare Trace to determine if a rule is triggering for a specific URL.