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<?php
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namespace Aws\CloudFront;
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/**
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 * @internal
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 */
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class Signer
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{
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    private $keyPairId;
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    private $pkHandle;
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    /**
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     * A signer for creating the signature values used in CloudFront signed URLs
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     * and signed cookies.
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     *
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     * @param $keyPairId  string ID of the key pair
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     * @param $privateKey string Path to the private key used for signing
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     * @param $passphrase string Passphrase to private key file, if one exists
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     *
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     * @throws \RuntimeException if the openssl extension is missing
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     * @throws \InvalidArgumentException if the private key cannot be found.
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     */
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    public function __construct($keyPairId, $privateKey, $passphrase = "")
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    {
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        if (!extension_loaded('openssl')) {
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            //@codeCoverageIgnoreStart
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            throw new \RuntimeException('The openssl extension is required to '
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                . 'sign CloudFront urls.');
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            //@codeCoverageIgnoreEnd
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        }
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        $this->keyPairId = $keyPairId;
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        if (!$this->pkHandle = openssl_pkey_get_private($privateKey, $passphrase)) {
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            if (!file_exists($privateKey)) {
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                throw new \InvalidArgumentException("PK file not found: $privateKey");
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            }
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            $this->pkHandle = openssl_pkey_get_private("file://$privateKey", $passphrase);
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            if (!$this->pkHandle) {
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                $errorMessages = [];
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                while(($newMessage = openssl_error_string()) !== false){
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                    $errorMessages[] = $newMessage;
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                }
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                throw new \InvalidArgumentException(implode("\n",$errorMessages));
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            }
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        }
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    }
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    public function __destruct()
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    {
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        if (PHP_MAJOR_VERSION < 8) {
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            $this->pkHandle && openssl_pkey_free($this->pkHandle);
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        }
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    }
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    /**
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     * Create the values used to construct signed URLs and cookies.
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     *
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     * @param string              $resource     The CloudFront resource to which
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     *                                          this signature will grant access.
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     *                                          Not used when a custom policy is
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     *                                          provided.
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     * @param string|integer|null $expires      UTC Unix timestamp used when
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     *                                          signing with a canned policy.
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     *                                          Not required when passing a
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     *                                          custom $policy.
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     * @param string              $policy       JSON policy. Use this option when
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     *                                          creating a signature for a custom
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     *                                          policy.
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     *
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     * @return array The values needed to construct a signed URL or cookie
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     * @throws \InvalidArgumentException  when not provided either a policy or a
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     *                                    resource and a expires
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     * @throws \RuntimeException when generated signature is empty
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     *
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     * @link http://docs.aws.amazon.com/AmazonCloudFront/latest/DeveloperGuide/private-content-signed-cookies.html
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     */
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    public function getSignature($resource = null, $expires = null, $policy = null)
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    {
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        $signatureHash = [];
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        if ($policy) {
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            $policy = preg_replace('/\s/s', '', $policy);
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            $signatureHash['Policy'] = $this->encode($policy);
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        } elseif ($resource && $expires) {
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            $expires = (int) $expires; // Handle epoch passed as string
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            $policy = $this->createCannedPolicy($resource, $expires);
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            $signatureHash['Expires'] = $expires;
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        } else {
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            throw new \InvalidArgumentException('Either a policy or a resource'
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                . ' and an expiration time must be provided.');
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        }
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        $signatureHash['Signature'] = $this->encode($this->sign($policy));
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        $signatureHash['Key-Pair-Id'] = $this->keyPairId;
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        return $signatureHash;
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    }
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    private function createCannedPolicy($resource, $expiration)
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    {
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        return json_encode([
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            'Statement' => [
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                [
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                    'Resource' => $resource,
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                    'Condition' => [
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                        'DateLessThan' => ['AWS:EpochTime' => $expiration],
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                    ],
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                ],
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            ],
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        ], JSON_UNESCAPED_SLASHES);
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    }
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    private function sign($policy)
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    {
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        $signature = '';
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        if(!openssl_sign($policy, $signature, $this->pkHandle)) {
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            $errorMessages = [];
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            while(($newMessage = openssl_error_string()) !== false) {
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                $errorMessages[] = $newMessage;
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            }
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            $exceptionMessage = "An error has occurred when signing the policy";
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            if (count($errorMessages) > 0) {
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                $exceptionMessage = implode("\n", $errorMessages);
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            }
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            throw new \RuntimeException($exceptionMessage);
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        }
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        return $signature;
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    }
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    private function encode($policy)
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    {
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        return strtr(base64_encode($policy), '+=/', '-_~');
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    }
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}