nextcloud-server/lib/private/AppFramework/Middleware/Security/CORSMiddleware.php

<?php

/**
 * SPDX-FileCopyrightText: 2016-2024 Nextcloud GmbH and Nextcloud contributors
 * SPDX-FileCopyrightText: 2016 ownCloud, Inc.
 * SPDX-License-Identifier: AGPL-3.0-only
 */
namespace OC\AppFramework\Middleware\Security;

use OC\AppFramework\Middleware\Security\Exceptions\SecurityException;
use OC\AppFramework\Utility\ControllerMethodReflector;
use OC\Authentication\Exceptions\PasswordLoginForbiddenException;
use OC\User\Session;
use OCP\AppFramework\Controller;
use OCP\AppFramework\Http;
use OCP\AppFramework\Http\Attribute\CORS;
use OCP\AppFramework\Http\Attribute\PublicPage;
use OCP\AppFramework\Http\JSONResponse;
use OCP\AppFramework\Http\Response;
use OCP\AppFramework\Middleware;
use OCP\IRequest;
use OCP\ISession;
use OCP\Security\Bruteforce\IThrottler;
use Psr\Log\LoggerInterface;
use ReflectionMethod;

/**
 * This middleware sets the correct CORS headers on a response if the
 * controller has the @CORS annotation. This is needed for webapps that want
 * to access an API and don't run on the same domain, see
 * https://developer.mozilla.org/en-US/docs/Web/HTTP/Access_control_CORS
 */
class CORSMiddleware extends Middleware {
	/** @var IRequest */
	private $request;
	/** @var ControllerMethodReflector */
	private $reflector;
	/** @var Session */
	private $session;
	/** @var IThrottler */
	private $throttler;

	public function __construct(IRequest $request,
		ControllerMethodReflector $reflector,
		Session $session,
		IThrottler $throttler,
		private readonly LoggerInterface $logger,
	) {
		$this->request = $request;
		$this->reflector = $reflector;
		$this->session = $session;
		$this->throttler = $throttler;
	}

	/**
	 * This is being run in normal order before the controller is being
	 * called which allows several modifications and checks
	 *
	 * @param Controller $controller the controller that is being called
	 * @param string $methodName the name of the method that will be called on
	 *                           the controller
	 * @throws SecurityException
	 * @since 6.0.0
	 */
	public function beforeController($controller, $methodName) {
		$reflectionMethod = new ReflectionMethod($controller, $methodName);

		// ensure that @CORS annotated API routes are not used in conjunction
		// with session authentication since this enables CSRF attack vectors
		if ($this->hasAnnotationOrAttribute($reflectionMethod, 'CORS', CORS::class) &&
			(!$this->hasAnnotationOrAttribute($reflectionMethod, 'PublicPage', PublicPage::class) || $this->session->isLoggedIn())) {
			$user = array_key_exists('PHP_AUTH_USER', $this->request->server) ? $this->request->server['PHP_AUTH_USER'] : null;
			$pass = array_key_exists('PHP_AUTH_PW', $this->request->server) ? $this->request->server['PHP_AUTH_PW'] : null;

			// Allow to use the current session if a CSRF token is provided
			if ($this->request->passesCSRFCheck()) {
				return;
			}
			// Skip CORS check for requests with AppAPI auth.
			if ($this->session->getSession() instanceof ISession && $this->session->getSession()->get('app_api') === true) {
				return;
			}
			$this->session->logout();
			try {
				if ($user === null || $pass === null || !$this->session->logClientIn($user, $pass, $this->request, $this->throttler)) {
					throw new SecurityException('CORS requires basic auth', Http::STATUS_UNAUTHORIZED);
				}
			} catch (PasswordLoginForbiddenException $ex) {
				throw new SecurityException('Password login forbidden, use token instead', Http::STATUS_UNAUTHORIZED);
			}
		}
	}

	/**
	 * @template T
	 *
	 * @param ReflectionMethod $reflectionMethod
	 * @param string $annotationName
	 * @param class-string<T> $attributeClass
	 * @return boolean
	 */
	protected function hasAnnotationOrAttribute(ReflectionMethod $reflectionMethod, string $annotationName, string $attributeClass): bool {
		if ($this->reflector->hasAnnotation($annotationName)) {
			return true;
		}


		if (!empty($reflectionMethod->getAttributes($attributeClass))) {
			$this->logger->debug($reflectionMethod->getDeclaringClass()->getName() . '::' . $reflectionMethod->getName() . ' uses the @' . $annotationName . ' annotation and should use the #[' . $attributeClass . '] attribute instead');
			return true;
		}

		return false;
	}

	/**
	 * This is being run after a successful controller method call and allows
	 * the manipulation of a Response object. The middleware is run in reverse order
	 *
	 * @param Controller $controller the controller that is being called
	 * @param string $methodName the name of the method that will be called on
	 *                           the controller
	 * @param Response $response the generated response from the controller
	 * @return Response a Response object
	 * @throws SecurityException
	 */
	public function afterController($controller, $methodName, Response $response) {
		// only react if it's a CORS request and if the request sends origin and

		if (isset($this->request->server['HTTP_ORIGIN'])) {
			$reflectionMethod = new ReflectionMethod($controller, $methodName);
			if ($this->hasAnnotationOrAttribute($reflectionMethod, 'CORS', CORS::class)) {
				// allow credentials headers must not be true or CSRF is possible
				// otherwise
				foreach ($response->getHeaders() as $header => $value) {
					if (strtolower($header) === 'access-control-allow-credentials' &&
					   strtolower(trim($value)) === 'true') {
						$msg = 'Access-Control-Allow-Credentials must not be '.
							   'set to true in order to prevent CSRF';
						throw new SecurityException($msg);
					}
				}

				$origin = $this->request->server['HTTP_ORIGIN'];
				$response->addHeader('Access-Control-Allow-Origin', $origin);
			}
		}
		return $response;
	}

	/**
	 * If an SecurityException is being caught return a JSON error response
	 *
	 * @param Controller $controller the controller that is being called
	 * @param string $methodName the name of the method that will be called on
	 *                           the controller
	 * @param \Exception $exception the thrown exception
	 * @throws \Exception the passed in exception if it can't handle it
	 * @return Response a Response object or null in case that the exception could not be handled
	 */
	public function afterException($controller, $methodName, \Exception $exception) {
		if ($exception instanceof SecurityException) {
			$response = new JSONResponse(['message' => $exception->getMessage()]);
			if ($exception->getCode() !== 0) {
				$response->setStatus($exception->getCode());
			} else {
				$response->setStatus(Http::STATUS_INTERNAL_SERVER_ERROR);
			}
			return $response;
		}

		throw $exception;
	}
}