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<?php
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namespace Aws\Signature;
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use Aws\Exception\UnresolvedSignatureException;
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use Aws\Token\BearerTokenAuthorization;
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/**
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 * Signature providers.
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 *
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 * A signature provider is a function that accepts a version, service, and
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 * region and returns a {@see SignatureInterface} object on success or NULL if
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 * no signature can be created from the provided arguments.
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 *
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 * You can wrap your calls to a signature provider with the
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 * {@see SignatureProvider::resolve} function to ensure that a signature object
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 * is created. If a signature object is not created, then the resolve()
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 * function will throw a {@see Aws\Exception\UnresolvedSignatureException}.
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 *
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 *     use Aws\Signature\SignatureProvider;
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 *     $provider = SignatureProvider::defaultProvider();
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 *     // Returns a SignatureInterface or NULL.
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 *     $signer = $provider('v4', 's3', 'us-west-2');
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 *     // Returns a SignatureInterface or throws.
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 *     $signer = SignatureProvider::resolve($provider, 'no', 's3', 'foo');
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 *
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 * You can compose multiple providers into a single provider using
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 * {@see Aws\or_chain}. This function accepts providers as arguments and
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 * returns a new function that will invoke each provider until a non-null value
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 * is returned.
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 *
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 *     $a = SignatureProvider::defaultProvider();
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 *     $b = function ($version, $service, $region) {
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 *         if ($version === 'foo') {
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 *             return new MyFooSignature();
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 *         }
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 *     };
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 *     $c = \Aws\or_chain($a, $b);
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 *     $signer = $c('v4', 'abc', '123');     // $a handles this.
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 *     $signer = $c('foo', 'abc', '123');    // $b handles this.
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 *     $nullValue = $c('???', 'abc', '123'); // Neither can handle this.
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 */
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class SignatureProvider
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{
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    private static $s3v4SignedServices = [
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        's3' => true,
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        's3control' => true,
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        's3-object-lambda' => true,
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    ];
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    /**
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     * Resolves and signature provider and ensures a non-null return value.
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     *
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     * @param callable $provider Provider function to invoke.
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     * @param string   $version  Signature version.
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     * @param string   $service  Service name.
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     * @param string   $region   Region name.
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     *
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     * @return SignatureInterface
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     * @throws UnresolvedSignatureException
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     */
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    public static function resolve(callable $provider, $version, $service, $region)
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    {
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        $result = $provider($version, $service, $region);
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        if ($result instanceof SignatureInterface
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            || $result instanceof BearerTokenAuthorization
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        ) {
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            return $result;
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        }
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        throw new UnresolvedSignatureException(
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            "Unable to resolve a signature for $version/$service/$region.\n"
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            . "Valid signature versions include v4 and anonymous."
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        );
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    }
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    /**
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     * Default SDK signature provider.
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     *
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     * @return callable
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     */
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    public static function defaultProvider()
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    {
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        return self::memoize(self::version());
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    }
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    /**
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     * Creates a signature provider that caches previously created signature
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     * objects. The computed cache key is the concatenation of the version,
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     * service, and region.
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     *
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     * @param callable $provider Signature provider to wrap.
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     *
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     * @return callable
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     */
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    public static function memoize(callable $provider)
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    {
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        $cache = [];
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        return function ($version, $service, $region) use (&$cache, $provider) {
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            $key = "($version)($service)($region)";
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            if (!isset($cache[$key])) {
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                $cache[$key] = $provider($version, $service, $region);
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            }
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            return $cache[$key];
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        };
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    }
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    /**
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     * Creates signature objects from known signature versions.
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     *
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     * This provider currently recognizes the following signature versions:
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     *
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     * - v4: Signature version 4.
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     * - anonymous: Does not sign requests.
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     *
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     * @return callable
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     */
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    public static function version()
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    {
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        return function ($version, $service, $region) {
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            switch ($version) {
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                case 's3v4':
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                case 'v4':
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                    return !empty(self::$s3v4SignedServices[$service])
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                        ? new S3SignatureV4($service, $region)
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                        : new SignatureV4($service, $region);
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                case 'v4a':
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                    return !empty(self::$s3v4SignedServices[$service])
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                        ? new S3SignatureV4($service, $region, ['use_v4a' => true])
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                        : new SignatureV4($service, $region, ['use_v4a' => true]);
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                case 'v4-unsigned-body':
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                    return !empty(self::$s3v4SignedServices[$service])
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                    ? new S3SignatureV4($service, $region, ['unsigned-body' => 'true'])
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                    : new SignatureV4($service, $region, ['unsigned-body' => 'true']);
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                case 'bearer':
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                    return new BearerTokenAuthorization();
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                case 'anonymous':
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                    return new AnonymousSignature();
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                default:
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                    return null;
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            }
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        };
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    }
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}