LmcCors

LmcCors is a simple Laminas MVC module that helps you to deal with Cross-Origin Resource Sharing (CORS).

What is LmcCors ?

LmcCors is a Laminas MVC module that allow to easily configure your Laminas MVC application so that it automatically builds HTTP responses that follow the CORS documentation.

Installation

Install the module by typing (or add it to your composer.json file):

$ composer require lm-commons/lmc-cors

Then, enable it by adding "LmcCors" in your application.config.php or modules.config.php file. Alternatively, the module will be added to the configuration during installation by the Laminas Component Installer

By default, LmcCors is configured to deny every CORS requests. To change that, you need to copy the config/lmc_cors.global.php.dist file to your autoload folder (remove the .dist extension), and modify it to suit your needs.

Documentation

What is CORS ?

CORS is a mechanism that allows to perform cross-origin requests from your browser.

For instance, let's say that your website is hosted in the domain http://example.com. By default, user agents will not be allowed to perform AJAX requests to another domain for security reasons (for instance http://funny-domain.com).

With CORS, you can allow your server to reply to such requests.

You can find better documentation on how CORS works on the web:

• Mozilla documentation about CORS
• CORS server flowchart

Event registration

LmcCors registers the LmcCors\Mvc\CorsRequestListener with the MvcEvent::EVENT_ROUTE event, with a priority of 2. This means that this listener is executed BEFORE the route has been matched.

Configuring the module

As by default, all the various options are set globally for all routes:

• allowed_origins: (array) List of allowed origins. To allow any origin, you can use the wildcard (*) character. If multiple origins are specified, LmcCors will automatically check the "Origin" header's value, and only return the allowed domain (if any) in the "Allow-Access-Control-Origin" response header. To allow any sub-domain, you can prefix the domain with the wildcard character (i.e. *.example.com). Please note that you don't need to add your host URI (so if your website is hosted as "example.com", "example.com" is automatically allowed.
• allowed_methods: (array) List of allowed HTTP methods. Those methods will be returned for the preflight request to indicate which methods are allowed to the user agent. You can even specify custom HTTP verbs.
• allowed_headers: (array) List of allowed headers that will be returned for the preflight request. This indicates to the user agent which headers are permitted to be sent when doing the actual request.
• max_age: (int) Maximum age (seconds) the preflight request should be cached by the user agent. This prevents the user agent from sending a preflight request for each request.
• exposed_headers: (array) List of response headers that are allowed to be read in the user agent. Please note that some browsers do not implement this feature correctly.
• allowed_credentials: (boolean) If true, it allows the browser to send cookies along with the request.

If you want to configure specific routes, you can add LmcCors\Options\CorsOptions::ROUTE_PARAM to your route configuration:

<?php

return [
    'lmc_cors' => [
        'allowed_origins' => ['*'],
        'allowed_methods' => ['GET', 'POST', 'DELETE'],
    ],
    'router' => [
        'routes' => [
            'readOnlyRoute' => [
                'type' => 'literal',
                'options' => [
                    'route' => '/foo/bar',
                    'defaults' => [
                        // This will replace allowed_methods configuration to only allow GET requests
                        // and only allow a specific origin instead of the wildcard origin
                        LmcCors\Options\CorsOptions::ROUTE_PARAM => [
                            'allowed_origins' => ['http://example.org'],
                            'allowed_methods' => ['GET'],
                        ],
                    ],
                ],
            ],
            'someAjaxCalls' => [
                'type' => 'literal',
                'options' => [
                    'route' => '/ajax',
                    'defaults' => [
                        // This overrides the wildcard origin
                        LmcCors\Options\CorsOptions::ROUTE_PARAM => [
                            'allowed_origins' => ['http://example.org'],
                        ],
                    ],
                ],
                'may_terminate' => false,
                'child_routes' => [
                    'blog' => [
                        'type' => 'literal',
                        'options' => [
                            'route' => '/blogpost',
                            'defaults' => [
                                // This would only allow `http://example.org` to GET this route
                                \LmcCors\Options\CorsOptions::ROUTE_PARAM => [
                                    'allowed_methods' => ['GET'],
                                ],
                            ],
                        ],
                        'may_terminate' => true,
                        'child_routes' => [
                            'delete' => [
                                'type' => 'segment',
                                'options' => [
                                    'route' => ':id',
                                    // This would only allow origin `http://example.org` to apply DELETE on this route
                                    'defaults' => [
                                        \LmcCors\Options\CorsOptions::ROUTE_PARAM => [
                                            'allowed_methods' => ['DELETE'],
                                        ],
                                    ],
                                ],
                            ],
                        ],
                    ],
                ],
            ],
        ],
    ],
];

Preflight request

If LmcCors detects a preflight CORS request, a new HTTP response will be created, and LmcCors will send the appropriate headers according to your configuration. The response will always be sent with a 200 status code (OK).

Please note that this will also prevent further MVC steps from being executed, since all subsequent MVC steps are skipped till Laminas\Mvc\MvcEvent::EVENT_FINISH, which is responsible for actually sending the response.

Actual request

When an actual request is made, LmcCors first checks if the origin is allowed. If it is not, then a new response with a 403 status code (Forbidden) is created and sent.

Please note that this will also prevent further MVC steps from being executed, since all subsequent MVC steps are skipped till Laminas\Mvc\MvcEvent::EVENT_FINISH, which is responsible for actually sending the response.

If the origin is allowed, LmcCors will just add the appropriate headers to the request produced by Laminas\Mvc.

Security concerns

Don't use this module to secure your application! You must use a proper authorization module, like BjyAuthorize, LmcRbacMvc or SpiffyAuthorize.

LmcCors only allows to accept or refuse a cross-origin request.

Custom schemes

Internally, LmcCors uses Laminas\Uri\UriFactory class. If you are using custom schemes (for instance if you are testing your API with some Google Chrome extensions), you need to add support for those schemes by adding them to the UriFactory config (please refer to the doc).

Example

To register the chrome-extension custom scheme in your API, simply add:

use Laminas\Uri\UriFactory;

UriFactory::registerScheme('chrome-extension', 'Laminas\Uri\Uri');

to the onBootstrap() method in module/Application/Module.php.

Registering the chrome-extension custom scheme like this allows you to use Google Chrome extensions for testing your API.