apache_request_headers() returns an associative array of all the HTTP headers in the current request. This is only supported when PHP runs as an Apache module.
Note: Prior to PHP 4.3.0, apache_request_headers() was called getallheaders(). After PHP 4.3.0, getallheaders() is an alias for apache_request_headers().
Note: You can also get at the value of the common CGI variables by reading them from the environment, which works whether or not you are using PHP as an Apache module. Use phpinfo() to see a list of all of the available environment variables.