Setting up CORS

CORS - Cross origin resource sharing

A good flowchart for implementing CORS support Reference:

CORS server flowchart

You can test your CORS Support here: http://www.test-cors.org/

You can read the specification here: https://www.w3.org/TR/cors/

The simple solution

For simple CORS requests, the server only needs to add the following header to its response:

Access-Control-Allow-Origin: <domain>, … | *

The following code should enable lazy CORS.

$app->options('/{routes:.+}', function ($request, $response, $args) {
    return $response;
});
$app->add(function ($req, $res, $next) {
    $response = $next($req, $res);
    return $response
            ->withHeader('Access-Control-Allow-Origin', 'http://mysite')
            ->withHeader('Access-Control-Allow-Headers', 'X-Requested-With, Content-Type, Accept, Origin, Authorization')
            ->withHeader('Access-Control-Allow-Methods', 'GET, POST, PUT, DELETE, PATCH, OPTIONS');
});

Add the following route as the last route:

// Catch-all route to serve a 404 Not Found page if none of the routes match
// NOTE: make sure this route is defined last
$app->map(['GET', 'POST', 'PUT', 'DELETE', 'PATCH'], '/{routes:.+}', function($req, $res) {
    $handler = $this->notFoundHandler; // handle using the default Slim page not found handler
    return $handler($req, $res);
});

Access-Control-Allow-Methods

The following middleware can be used to query Slim’s router and get a list of methods a particular pattern implements.

Here is a complete example application:

require __DIR__ . "/vendor/autoload.php";
// This Slim setting is required for the middleware to work
$app = new Slim\App([
    "settings"  => [
        "determineRouteBeforeAppMiddleware" => true,
    ]
]);
// This is the middleware
// It will add the Access-Control-Allow-Methods header to every request
$app->add(function($request, $response, $next) {
    $route = $request->getAttribute("route");
    $methods = [];
    if (!empty($route)) {
        $pattern = $route->getPattern();
        foreach ($this->router->getRoutes() as $route) {
            if ($pattern === $route->getPattern()) {
                $methods = array_merge_recursive($methods, $route->getMethods());
            }
        }
        //Methods holds all of the HTTP Verbs that a particular route handles.
    } else {
        $methods[] = $request->getMethod();
    }
    $response = $next($request, $response);
    return $response->withHeader("Access-Control-Allow-Methods", implode(",", $methods));
});
$app->get("/api/{id}", function($request, $response, $arguments) {
});
$app->post("/api/{id}", function($request, $response, $arguments) {
});
$app->map(["DELETE", "PATCH"], "/api/{id}", function($request, $response, $arguments) {
});
// Pay attention to this when you are using some javascript front-end framework and you are using groups in slim php
$app->group('/api', function () {
    // Due to the behaviour of browsers when sending PUT or DELETE request, you must add the OPTIONS method. Read about preflight.
    $this->map(['PUT', 'OPTIONS'], '/{user_id:[0-9]+}', function ($request, $response, $arguments) {
        // Your code here...
    });
});
$app->run();

A big thank you to tuupola for coming up with this!