How to dynamically set HTTP Header in Apache 2.2?

Question

Seems like this should be easy, but I cannot figure out the syntax. In Apache, I want to use the value of an existing request header to set a new request header. Some simple non-working code that illustrates what I'd like to do:

RequestHeader set X-Custom-Host-Header "%{HTTP_HOST}e" 

Ideally, this would make a new HTTP header in the request called "X-Custom-Host-Header" that contains the value of the existing Host header. But it does not. Perhaps I need to copy the existing header into an environment variable first? (If so, I can't figure out how to do that either.)

I feel like I'm missing something obvious, but I've gone over the Apache docs and I can't figure it out. Thanks for any help.

Solution

The FOOBAR in %{FOOBAR}e should be an environment variable, but HTTP_HOST is a server variable.

If you really want to do that, you may try:

RewriteRule (.*) $1 [E=custom_host:%{HTTP_HOST}]
RequestHeader set X-Custom-Host-Header "%{custom_host}e"

or

RewriteCond %{HTTP_HOST} (.*)
RewriteRule (.*) $1 [E=custom_host:%1]
RequestHeader set X-Custom-Host-Header "%{custom_host}e"

or

SetEnvIf Host (.*) custom_host=$1
RequestHeader set X-Custom-Host-Header "%{custom_host}e"

All untested.

Not sure of the first one, but the second and third one should work.

Comments

[Lauri Lehtinen]

I tried all of these, none of them worked. The header is not being set.

[jo pizzamaker]

I tried the third form, and also set a response header. The response header was set properly.

[jo pizzamaker]

Third form worked for on getting the request header, too.

[stephen mulcahy]

The 3rd option also worked for me and the explanation makes sense - thanks