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<?php namespace Arcanedev\Stripe; |
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/** |
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* Class WebhookSignature |
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* |
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* @package Arcanedev\Stripe |
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* @author ARCANEDEV <[email protected]> |
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*/ |
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abstract class WebhookSignature |
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{ |
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/* ----------------------------------------------------------------- |
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| Constants |
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| ----------------------------------------------------------------- |
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*/ |
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const EXPECTED_SCHEME = 'v1'; |
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/* ----------------------------------------------------------------- |
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| Main Methods |
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| ----------------------------------------------------------------- |
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*/ |
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/** |
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* Verifies the signature header sent by Stripe. |
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* Throws a SignatureVerification exception if the verification fails for any reason. |
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* |
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* @param string $payload The payload sent by Stripe. |
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* @param string $header The contents of the signature header sent by Stripe. |
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* @param string $secret Secret used to generate the signature. |
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* @param int $tolerance Maximum difference allowed between the header's timestamp and the current time |
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* |
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* @return bool |
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* |
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* @throws \Arcanedev\Stripe\Exceptions\SignatureVerificationException |
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*/ |
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public static function verifyHeader($payload, $header, $secret, $tolerance = null) |
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{ |
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// Extract timestamp and signatures from header |
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$timestamp = self::getTimestamp($header); |
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$signatures = self::getSignatures($header, self::EXPECTED_SCHEME); |
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if ($timestamp == -1) { |
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throw new Exceptions\SignatureVerificationException( |
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'Unable to extract timestamp and signatures from header', |
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$header, |
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$payload |
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); |
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} |
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if (empty($signatures)) { |
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throw new Exceptions\SignatureVerificationException( |
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"No signatures found with expected scheme", $header, $payload |
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); |
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} |
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// Check if expected signature is found in list of signatures from header |
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$signedPayload = "$timestamp.$payload"; |
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$expectedSignature = self::computeSignature($signedPayload, $secret); |
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$signatureFound = false; |
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foreach ($signatures as $signature) { |
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if (Utilities\Util::secureCompare($expectedSignature, $signature)) { |
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$signatureFound = true; |
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break; |
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} |
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} |
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if ( ! $signatureFound) { |
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throw new Exceptions\SignatureVerificationException( |
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'No signatures found matching the expected signature for payload', |
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$header, |
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$payload |
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); |
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} |
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// Check if timestamp is within tolerance |
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if (($tolerance > 0) && ((time() - $timestamp) > $tolerance)) { |
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throw new Exceptions\SignatureVerificationException( |
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'Timestamp outside the tolerance zone', |
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1 |
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$header, |
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$payload |
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); |
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} |
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return true; |
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} |
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/* ----------------------------------------------------------------- |
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| Other Methods |
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| ----------------------------------------------------------------- |
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*/ |
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/** |
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* Extracts the timestamp in a signature header. |
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* |
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* @param string $header the signature header |
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* @return int the timestamp contained in the header, or -1 if no valid timestamp is found |
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*/ |
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private static function getTimestamp($header) |
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{ |
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$items = explode(',', $header); |
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foreach ($items as $item) { |
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$itemParts = explode('=', $item, 2); |
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if ($itemParts[0] == 't') { |
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if ( ! is_numeric($itemParts[1])) return -1; |
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return intval($itemParts[1]); |
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} |
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} |
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return -1; |
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} |
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/** |
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* Extracts the signatures matching a given scheme in a signature header. |
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* |
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* @param string $header The signature header |
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* @param string $scheme The signature scheme to look for. |
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* |
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* @return array The list of signatures matching the provided scheme. |
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*/ |
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private static function getSignatures($header, $scheme) |
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{ |
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27 |
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$signatures = []; |
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$items = explode(',', $header); |
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27 |
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foreach ($items as $item) { |
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$itemParts = explode('=', $item, 2); |
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if ($itemParts[0] == $scheme) { |
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array_push($signatures, $itemParts[1]); |
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} |
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} |
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return $signatures; |
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} |
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/** |
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* Computes the signature for a given payload and secret. |
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* |
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* The current scheme used by Stripe ("v1") is HMAC/SHA-256. |
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* |
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* @param string $payload The payload to sign. |
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* @param string $secret The secret used to generate the signature. |
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* |
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* @return string The signature as a string. |
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*/ |
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18 |
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private static function computeSignature($payload, $secret) |
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{ |
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return hash_hmac('sha256', $payload, $secret); |
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} |
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} |
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|
ARCANEDEV /
Stripe
