Ajax setRequestHeader, i can't get values on the server side - php

Question

I am sending request header using XMLHttpRequest :
liveXhr.open("GET", url, true);
liveXhr.setRequestHeader("keychain_id", signatureKEYCHAINID);
liveXhr.setRequestHeader("timestamp", signatureTS);
liveXhr.setRequestHeader("signature", signature);
liveXhr.send();
On my localhost everything is fine, when i log :
error_log(print_r(apache_request_headers(), true));
I have this :
[Host] => localhost
[Connection] => keep-alive
[Pragma] => no-cache
[Cache-Control] => no-cache
[timestamp] => 1478279032
[signature] => abcd
[keychain_id] => abcd
[User-Agent] => Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 ( KHTML, like Gecko) Chrome/52.0.2743.116 Safari/537.36
[Content-Type] => text/plain
I can get the values for timestamp, signature, keychain_id
On my preprod server for the same process :
...
[Access-Control-Request-Headers] => keychain_id, signature, timestamp
...
I can't get the values of timestamp, signature, keychain_id.
Is it an apache setting concern or something else ?

Answer 1

Try:
//array
$requestHeaders = apache_request_headers();
//get array item by name
$keyChainId = $requestHeaders['keychain_id'];
$timestamp = $requestHeaders['timestamp'];
$signature = $requestHeaders['signature'];
//print items
echo "- keychain_id = $keyChainId";
echo "\n- timestamp = $timestamp";
echo "\n- signature = $signature";
[Edited]
Try:
//not underscore
liveXhr.setRequestHeader("keychainid", KEYCHAINID);
...
//prefix HTTP_
var_dump($_SERVER['HTTP_TIMESTAMP']);
var_dump($_SERVER['HTTP_SIGNATURE']);
var_dump($_SERVER['HTTP_KEYCHAINID']);