digest-auth-remote-get.php

<?php

/**
 * Make a remote GET using DIGEST authentication.
 *
 * DIGEST authenticated requests require two GET requests:
 * 1. GET the www-authenticate header for nonce, realm, opaque, and other values
 * 2. GET the expected response body by constructing an 'Authorization' header
 *    with nonce, realm, and other values provided by the server.
 * 
 * @license MIT
 *
 * @param string $url API URL supporting DIGEST authentication.
 * @param string $username Username to be used in authentication.
 * @param string $password Password to be used in authentication.
 * @return string|false Response body on success, false on some form of failure.
 */
function hb_digest_auth_remote_get( $url, $username, $password ) {

	/*
	 * Makes an initial request for the server's provided headers
	 */
	$response = wp_remote_get( $url, $request );
	$header = wp_remote_retrieve_header( $response, 'www-authenticate' );
	if ( empty( $header ) ) {
		return false;
	}

	/*
	 * Parses the 'www-authenticate' header for nonce, realm and other values.
	 */
	preg_match_all( '#(([\w]+)=["]?([^\s"]+))#', $header, $matches );
	$server_bits = array();
	foreach( $matches[2] as $i => $key ) {
		$server_bits[ $key ] = $matches[3][ $i ];
	}

	$nc = '00000001';
	$path = parse_url( $url, PHP_URL_PATH );
	$client_nonce = uniqid();
	$ha1 = md5( $username . ':' . $server_bits['realm'] . ':' . $password );
	$ha2 = md5( 'GET:' . $path );
	// The order of this array matters, because it affects resulting hashed val
	$response_bits = array(
		$ha1,
		$server_bits['nonce'],
		$nc,
		$client_nonce,
		$server_bits['qop'],
		$ha2
	);

	$digest_header_values = array(
		'username'       => '"' . $username . '"',
		'realm'          => '"' . $server_bits['realm'] . '"',
		'nonce'          => '"' . $server_bits['nonce'] . '"',
		'uri'            => '"' . $path . '"',
		'response'       => '"' . md5( implode( ':', $response_bits ) ) . '"',
		'opaque'         => '"' . $server_bits['opaque'] . '"',
		'qop'            => $server_bits['qop'],
		'nc'             => $nc,
		'cnonce'         => '"' . $client_nonce . '"',
		);
	$digest_header = 'Digest ';
	foreach( $digest_header_values as $key => $value ) {
		$digest_header .= $key . '=' . $value . ', ';
	}
	$digest_header = rtrim( $digest_header, ', ' );

	$request = array(
		'headers'        => array(
			'Authorization'       => $digest_header,
		),
	);
	$response = wp_remote_get( $url, $request );
	if ( 200 !== wp_remote_retrieve_response_code( $response ) ) {
		return false;
	}
	return wp_remote_retrieve_body( $response );
}