use curl php library: http://php.net/manual/en/book.curl.php
direct example: CURL_EXEC:
<?php
// create a new cURL resource
$ch = curl_init();
// set URL and other appropriate options
curl_setopt($ch, CURLOPT_URL, "http://www.example.com/");
curl_setopt($ch, CURLOPT_HEADER, 0);
// grab URL and pass it to the browser
curl_exec($ch);
// close cURL resource, and free up system resources
curl_close($ch);
?>
As other's have mentioned, PHP's cURL functions will allow you to perform advanced HTTP requests. You can also use file_get_contents to access REST APIs:
$payload = file_get_contents('http://api.someservice.com/SomeMethod?param=value');
Starting with PHP 5 you can also create a stream context which will allow you to change headers or post data to the service.