HTTP request header modification rules
You can manipulate the headers of incoming HTTP requests through HTTP request header modification rules. Through these 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 cannot modify or remove HTTP request headers whose name starts with
cf-except for the
cf-connecting-ipHTTP request header, which you can remove.
You cannot modify the value of any header commonly used to identify the website visitor’s IP address, such as
x-real-ip. Additionally, you cannot remove the
You cannot set or modify the value of
cookieHTTP request headers, but you can remove these headers. Configuring a rule that removes the
cookieHTTP request header will remove all
cookieheaders 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. for consideration.