tec: Allow to change CSP header from controllers

For an extension, I needed to call a script from an external domain.
Unfortunately, the CSP headers didn't allow this domain and I had to
patch manually the FreshRSS FrontController for my extension. It's
obviously not a long-term solution since it has nothing to do in the
core of FRSS, and I don't want to apply this patch manually at each
update.

With this patch, I allow changing the CSP header from inside the
controller actions. It allows extensions to modify headers. It's also an
opportunity to remove a bit of code from the FrontController. I wasn't
happy with the previous implementation anyhow.

Reference: https://github.com/flusio/xExtension-Flus/commit/ed12d56#diff-ff12e33ed31b23bda327499fa6e84eccR143

2 files changed, 37 insertions, 0 deletions

diff --git a/lib/Minz/ActionController.php b/lib/Minz/ActionController.php
index 123b9054c..f60b5411d 100644
--- a/lib/Minz/ActionController.php
+++ b/lib/Minz/ActionController.php
@@ -9,6 +9,9 @@
  */
 class Minz_ActionController {
 	protected $view;
+	private $csp_policies = array(
+		'default-src' => "'self'",
+	);
 
 	/**
 	 * Constructeur
@@ -28,6 +31,39 @@ class Minz_ActionController {
 	}
 
 	/**
+	 * Set CSP policies.
+	 *
+	 * A default-src directive should always be given.
+	 *
+	 * References:
+	 * - https://developer.mozilla.org/en-US/docs/Web/HTTP/CSP
+	 * - https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy/default-src
+	 *
+	 * @param array $policies An array where keys are directives and values are sources.
+	 */
+	protected function _csp($policies) {
+		if (!isset($policies['default-src'])) {
+			$action = Minz_Request::controllerName() . '#' . Minz_Request::actionName();
+			Minz_Log::warning(
+				"Default CSP policy is not declared for action {$action}.",
+				ADMIN_LOG
+			);
+		}
+		$this->csp_policies = $policies;
+	}
+
+	/**
+	 * Send HTTP Content-Security-Policy header based on declared policies.
+	 */
+	public function declareCspHeader() {
+		$policies = [];
+		foreach ($this->csp_policies as $directive => $sources) {
+			$policies[] = $directive . ' ' . $sources;
+		}
+		header('Content-Security-Policy: ' . implode('; ', $policies));
+	}
+
+	/**
 	 * Méthodes à redéfinir (ou non) par héritage
 	 * firstAction est la première méthode exécutée par le Dispatcher
 	 * lastAction est la dernière
diff --git a/lib/Minz/Dispatcher.php b/lib/Minz/Dispatcher.php
index f05b285b5..7a1c3e1d7 100644
--- a/lib/Minz/Dispatcher.php
+++ b/lib/Minz/Dispatcher.php
@@ -50,6 +50,7 @@ class Minz_Dispatcher {
 				$this->controller->lastAction ();
 
 				if (!self::$needsReset) {
+					$this->controller->declareCspHeader();
 					$this->controller->view ()->build ();
 				}
 			} catch (Minz_Exception $e) {