Create a URL signature using PHP - Amazon CloudFront

Create a URL signature using PHP

Any web server that runs PHP can use this PHP example code to create policy statements and signatures for private CloudFront distributions. The full example creates a functioning webpage with signed URL links that play a video stream using CloudFront streaming. You can download the full example at https://docs.aws.amazon.com/AmazonCloudFront/latest/DeveloperGuide/samples/demo-php.zip.

You can also create signed URLs by using the UrlSigner class in the AWS SDK for PHP. For more information, see Class UrlSigner in the AWS SDK for PHP API Reference.

Note

Creating a URL signature is just one part of the process of serving private content using a signed URL. For more information about the entire process, see Using signed URLs.

Sample: RSA SHA-1 signature

In the following code example, the function rsa_sha1_sign hashes and signs the policy statement. The arguments required are a policy statement and the private key that corresponds with a public key that’s in a trusted key group for your distribution. Next, the url_safe_base64_encode function creates a URL-safe version of the signature.

function rsa_sha1_sign($policy, $private_key_filename) { $signature = ""; // load the private key $fp = fopen($private_key_filename, "r"); $priv_key = fread($fp, 8192); fclose($fp); $pkeyid = openssl_get_privatekey($priv_key); // compute signature openssl_sign($policy, $signature, $pkeyid); // free the key from memory openssl_free_key($pkeyid); return $signature; } function url_safe_base64_encode($value) { $encoded = base64_encode($value); // replace unsafe characters +, = and / with // the safe characters -, _ and ~ return str_replace( array('+', '=', '/'), array('-', '_', '~'), $encoded); }

Example: create canned policy

The following example code constructs a canned policy statement for the signature. For more information about canned policies, see Creating a signed URL using a canned policy.

Note

The $expires variable is a date/time stamp that must be an integer, not a string.

function get_canned_policy_stream_name($video_path, $private_key_filename, $key_pair_id, $expires) { // this policy is well known by CloudFront, but you still need to sign it, // since it contains your parameters $canned_policy = '{"Statement":[{"Resource":"' . $video_path . '","Condition":{"DateLessThan":{"AWS:EpochTime":'. $expires . '}}}]}'; // sign the canned policy $signature = rsa_sha1_sign($canned_policy, $private_key_filename); // make the signature safe to be included in a url $encoded_signature = url_safe_base64_encode($signature); // combine the above into a stream name $stream_name = create_stream_name($video_path, null, $encoded_signature, $key_pair_id, $expires); // url-encode the query string characters to work around a flash player bug return encode_query_params($stream_name); }

Example: create a custom policy

The following example code constructs a custom policy statement for the signature. For more information about custom policies, see Creating a signed URL using a custom policy.

function get_custom_policy_stream_name($video_path, $private_key_filename, $key_pair_id, $policy) { // sign the policy $signature = rsa_sha1_sign($policy, $private_key_filename); // make the signature safe to be included in a url $encoded_signature = url_safe_base64_encode($signature); // combine the above into a stream name $stream_name = create_stream_name($video_path, $encoded_policy, $encoded_signature, $key_pair_id, null); // url-encode the query string characters to work around a flash player bug return encode_query_params($stream_name); }

Full code example

The following example code provides a complete demonstration of creating CloudFront signed URLs with PHP. You can download this full example at https://docs.aws.amazon.com/AmazonCloudFront/latest/DeveloperGuide/samples/demo-php.zip.

<?php function rsa_sha1_sign($policy, $private_key_filename) { $signature = ""; // load the private key $fp = fopen($private_key_filename, "r"); $priv_key = fread($fp, 8192); fclose($fp); $pkeyid = openssl_get_privatekey($priv_key); // compute signature openssl_sign($policy, $signature, $pkeyid); // free the key from memory openssl_free_key($pkeyid); return $signature; } function url_safe_base64_encode($value) { $encoded = base64_encode($value); // replace unsafe characters +, = and / with the safe characters -, _ and ~ return str_replace( array('+', '=', '/'), array('-', '_', '~'), $encoded); } function create_stream_name($stream, $policy, $signature, $key_pair_id, $expires) { $result = $stream; // if the stream already contains query parameters, attach the new query parameters to the end // otherwise, add the query parameters $separator = strpos($stream, '?') == FALSE ? '?' : '&'; // the presence of an expires time means we're using a canned policy if($expires) { $result .= $path . $separator . "Expires=" . $expires . "&Signature=" . $signature . "&Key-Pair-Id=" . $key_pair_id; } // not using a canned policy, include the policy itself in the stream name else { $result .= $path . $separator . "Policy=" . $policy . "&Signature=" . $signature . "&Key-Pair-Id=" . $key_pair_id; } // new lines would break us, so remove them return str_replace('\n', '', $result); } function encode_query_params($stream_name) { // Adobe Flash Player has trouble with query parameters being passed into it, // so replace the bad characters with their URL-encoded forms return str_replace( array('?', '=', '&'), array('%3F', '%3D', '%26'), $stream_name); } function get_canned_policy_stream_name($video_path, $private_key_filename, $key_pair_id, $expires) { // this policy is well known by CloudFront, but you still need to sign it, since it contains your parameters $canned_policy = '{"Statement":[{"Resource":"' . $video_path . '","Condition":{"DateLessThan":{"AWS:EpochTime":'. $expires . '}}}]}'; // the policy contains characters that cannot be part of a URL, so we base64 encode it $encoded_policy = url_safe_base64_encode($canned_policy); // sign the original policy, not the encoded version $signature = rsa_sha1_sign($canned_policy, $private_key_filename); // make the signature safe to be included in a URL $encoded_signature = url_safe_base64_encode($signature); // combine the above into a stream name $stream_name = create_stream_name($video_path, null, $encoded_signature, $key_pair_id, $expires); // URL-encode the query string characters to support Flash Player return encode_query_params($stream_name); } function get_custom_policy_stream_name($video_path, $private_key_filename, $key_pair_id, $policy) { // the policy contains characters that cannot be part of a URL, so we base64 encode it $encoded_policy = url_safe_base64_encode($policy); // sign the original policy, not the encoded version $signature = rsa_sha1_sign($policy, $private_key_filename); // make the signature safe to be included in a URL $encoded_signature = url_safe_base64_encode($signature); // combine the above into a stream name $stream_name = create_stream_name($video_path, $encoded_policy, $encoded_signature, $key_pair_id, null); // URL-encode the query string characters to support Flash Player return encode_query_params($stream_name); } // Path to your private key. Be very careful that this file is not accessible // from the web! $private_key_filename = '/home/test/secure/example-priv-key.pem'; $key_pair_id = 'K2JCJMDEHXQW5F'; $video_path = 'example.mp4'; $expires = time() + 300; // 5 min from now $canned_policy_stream_name = get_canned_policy_stream_name($video_path, $private_key_filename, $key_pair_id, $expires); $client_ip = $_SERVER['REMOTE_ADDR']; $policy = '{'. '"Statement":['. '{'. '"Resource":"'. $video_path . '",'. '"Condition":{'. '"IpAddress":{"AWS:SourceIp":"' . $client_ip . '/32"},'. '"DateLessThan":{"AWS:EpochTime":' . $expires . '}'. '}'. '}'. ']' . '}'; $custom_policy_stream_name = get_custom_policy_stream_name($video_path, $private_key_filename, $key_pair_id, $policy); ?> <html> <head> <title>CloudFront</title> <script type='text/javascript' src='https://example.cloudfront.net/player/swfobject.js'></script> </head> <body> <h1>Amazon CloudFront </h1> <h2>Canned Policy</h2> <h3>Expires at <?= gmdate('Y-m-d H:i:s T', $expires) ?></h3> <br /> <div id='canned'>The canned policy video will be here</div> <h2>Canned Policy</h2> <h3>Expires at <?= gmdate('Y-m-d H:i:s T', $expires) ?> only viewable by IP <?= $client_ip ?></h3> <div id='custom'>The custom policy video will be here</div> <!-- ************** Have to update the player.swf path to a real JWPlayer instance. The fake one means that external people cannot watch the video right now --> <script type='text/javascript'> var so_canned = new SWFObject('https://files.example.com/player.swf','mpl','640','360','9'); so_canned.addParam('allowfullscreen','true'); so_canned.addParam('allowscriptaccess','always'); so_canned.addParam('wmode','opaque'); so_canned.addVariable('file','<?= $canned_policy_stream_name ?>'); so_canned.addVariable('streamer','rtmp://example.cloudfront.net/cfx/st'); so_canned.write('canned'); var so_custom = new SWFObject('https://files.example.com/player.swf','mpl','640','360','9'); so_custom.addParam('allowfullscreen','true'); so_custom.addParam('allowscriptaccess','always'); so_custom.addParam('wmode','opaque'); so_custom.addVariable('file','<?= $custom_policy_stream_name ?>'); so_custom.addVariable('streamer','rtmp://example.cloudfront.net/cfx/st'); so_custom.write('custom'); </script> </body> </html>

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