PSR-7 and PSR-15 CORS Middleware

This middleware implements Cross-origin resource sharing. It supports both PSR-7 style doublepass and PSR-15 middleware standards. It has been tested with Slim Framework and Zend Expressive. Internally the middleware uses neomerx/cors-psr7 library for heavy lifting.

Install

Install using composer.

$ composer require tuupola/cors-middleware

Usage

Documentation assumes you have working knowledge of CORS. There are no mandatory parameters. If you are using Zend Expressive skeleton middlewares are added to file called config/pipeline.php. Note that you must disable the default ImplicitOptionsMiddleware for this middleware to work.

use Tuupola\Middleware\CorsMiddleware;

#$app->pipe(ImplicitOptionsMiddleware::class);
$app->pipe(CorsMiddleware::class);

Slim Framework does not have specified config files. Otherwise adding the middleware is similar with previous.

$app->add(new Tuupola\Middleware\CorsMiddleware);

Rest of the examples use Slim Framework.

If called without any parameters the following defaults are used.

$app->add(new Tuupola\Middleware\CorsMiddleware([
    "origin" => ["*"],
    "methods" => ["GET", "POST", "PUT", "PATCH", "DELETE"],
    "headers.allow" => [],
    "headers.expose" => [],
    "credentials" => false,
    "cache" => 0,
]));

$ curl "https://api.example.com/" \
    --request OPTIONS \
    --include
    --header "Access-Control-Request-Method: PUT" \
    --header "Origin: http://www.example.com"

HTTP/1.1 200 OK
Access-Control-Allow-Origin: http://www.example.com
Vary: Origin
Access-Control-Allow-Methods: GET, POST, PUT, PATCH, DELETE

However, you most likely want to change some of the defaults. For example if developing a REST API which supports caching and conditional requests you could use the following.

$app->add(new Tuupola\Middleware\CorsMiddleware([
    "origin" => ["*"],
    "methods" => ["GET", "POST", "PUT", "PATCH", "DELETE"],
    "headers.allow" => ["Authorization", "If-Match", "If-Unmodified-Since"],
    "headers.expose" => ["Etag"],
    "credentials" => true,
    "cache" => 86400
]));

$ curl "https://api.example.com/foo" \
    --request OPTIONS \
    --include \
    --header "Origin: http://www.example.com" \
    --header "Access-Control-Request-Method: PUT" \
    --header "Access-Control-Request-Headers: Authorization, If-Match"

HTTP/1.1 200 OK
Access-Control-Allow-Origin: http://www.example.com
Access-Control-Allow-Credentials: true
Vary: Origin
Access-Control-Max-Age: 86400
Access-Control-Allow-Methods: GET, POST, PUT, PATCH, DELETE
Access-Control-Allow-Headers: authorization, if-match, if-unmodified-since

$ curl "https://api.example.com/foo" \
    --request PUT \
    --include \
    --header "Origin: http://www.example.com"

HTTP/1.1 200 OK
Access-Control-Allow-Origin: http://www.example.com
Access-Control-Allow-Credentials: true
Vary: Origin
Access-Control-Expose-Headers: Etag

Parameters

Origin

By default all origins are allowed. You can limit allowed origins by passing them as an array.

$app->add(new Tuupola\Middleware\CorsMiddleware([
    "origin" => ["app-1.example.com", "app-2.example.com"]
]));

You can also use wildcards to define multiple origins at once. Wildcards are matched by using the fnmatch() function.

$app->add(new Tuupola\Middleware\CorsMiddleware([
    "origin" => ["*.example.com"]
]));

Methods

Methods can be passed either as an array or a callable which returns an array. Below example is for Zend Expressive where value of methods is dynamic depending on the requested route.

use Tuupola\Middleware\CorsMiddleware;
use Zend\Expressive\Router\RouteResult;

$app->pipe(new CorsMiddleware([
    "origin" => ["*"],
    "methods" => function($request) {
        $result = $request->getAttribute(RouteResult::class);
        $route = $result->getMatchedRoute();
        return $route->getAllowedMethods();
    }
]));

Same thing for Slim 3. This assumes you have not defined the OPTIONS route.

use Fastroute\Dispatcher;
use Tuupola\Middleware\CorsMiddleware;

$app->add(
    new CorsMiddleware([
        "origin" => ["*"],
        "methods" => function($request) use ($app) {
            $container = $app->getContainer();
            $dispatch = $container["router"]->dispatch($request);
            if (Dispatcher::METHOD_NOT_ALLOWED === $dispatch[0]) {
                return $dispatch[1];
            }
        }
    ])
);

Logger

The optional logger parameter allows you to pass in a PSR-3 compatible logger to help with debugging or other application logging needs.

$logger = Monolog\Logger("slim");
$rotating = new RotatingFileHandler(__DIR__ . "/logs/slim.log", 0, Logger::DEBUG);
$logger->pushHandler($rotating);

$app->add(new Tuupola\Middleware\CorsMiddleware([
    "logger" => $logger,
]));

Error

Error is called when CORS request fails. It receives last error message in arguments. This can be used for example to create application/json responses when CORS request fails.

$app->add(new Tuupola\Middleware\CorsMiddleware([
    "methods" => ["GET", "POST", "PUT"],
    "error" => function ($request, $response, $arguments) {
        $data["status"] = "error";
        $data["message"] = $arguments["message"];
        return $response
            ->withHeader("Content-Type", "application/json")
            ->write(json_encode($data, JSON_UNESCAPED_SLASHES | JSON_PRETTY_PRINT));
    }
]));

$ curl https://api.example.com/foo \
    --request OPTIONS \
    --include \
    --header "Access-Control-Request-Method: PATCH" \
    --header "Origin: http://www.example.com"

HTTP/1.1 401 Unauthorized
Content-Type: application/json
Content-Length: 83

{
    "status": "error",
    "message": "CORS requested method is not supported."
}

Server origin

If your same-origin requests contain an unnecessary Origin header, they might get blocked in case the server origin is not among the allowed origins already. In this case you can use the optional origin.server parameter to specify the origin of the server.

$app->add(new Tuupola\Middleware\CorsMiddleware([
    "origin.server" => "https://example.com"
]));

$ curl https://example.com/api \
    --request POST \
    --include \
    --header "Origin: https://example.com"

HTTP/1.1 200 OK

Testing

You can run tests either manually or automatically on every code change. Automatic tests require entr to work.

$ make test

$ brew install entr
$ make watch

Contributing

Please see CONTRIBUTING for details.

Security

If you discover any security related issues, please email tuupola@appelsiini.net instead of using the issue tracker.

License

The MIT License (MIT). Please see License File for more information.