Apache Custom Header with an environment variable

apache-2.4environment-variableshttp-headers

I try to set a custom HTTP Header with an environment variable** with Apache server 2.4.6 and headers_module.

I work inside a HTTP VHost on port 80.

Everything work as expected with basic example like:

Header set MyHeader "%D %t"

I have read the Apache Documentation of mod_headers : https://httpd.apache.org/docs/2.4/en/mod/mod_headers.html#header

It is said that one can access environment variable using
%{ENVVARNAME}e

(with ENVVARNAME the name of the ENV variable)

I also read other post but no real working answer:
Apache set custom header with an evironment variable

But my problem is to add a header than identify my Apache Server like the HOSTNAME environment value

I tried this

Header Set X-Serv %{HOSTNAME}e

No success : always display X-Serv:{null} instead of the value

I also tried :

SetEnv myvar ${HOSTNAME} Header set X-Serv %{myvar}e

No success : it displays in my HTTP Headers : X-Serv: %{myvar}e

I also tried some other various combinations:

Please note: My HOSTNAME environment variable exists and it display in 'env' command with the apache user owning the httpd process

Any idea?

Best Answer

You have to declare which system environment variables you want to be usable with the PassEnv directive

A working example would be:

PassEnv HOSTNAME
Header Set X-Serv %{HOSTNAME}e

Related Solutions

How to dynamically set HTTP Header in Apache 2.2

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.

How to escape spaces in Apache SetEnvIf value

In the end I figured it out for myself…

SetEnvIf Request_URI "^/example" "AUTH_KEY=a b"

… which looks odd, but works. It correctly sets AUTH_KEY to value a b

Hopefully this might save someone else's time in the future.

The details:- I am not a C programmer, but bumbling around on Google I found mod_setenvif.c listed at http://www.bvbcode.com/code/s6148jvr-385031

A function is called on line 405 (ap_getword_conf, for which I found detail at http://docstore.mik.ua/orelly/apache_mod/155.htm) which seems to parse strings, delimited by whitespace (but optionally encapsulated in quotes and accepting the use of escape characters).

I noticed that this happened before the sub-string returned by the function above being split by the '=' character (line 411, by function ap_getword). Thus quotes around the key=value pair, rather than just the value.

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