[FEATURE] Csrf token

- Added functionality to CsrfToken class.
- Added header support to Request class.
- Added option to set BaseCsrfVerifier class in RouterBase and
  SimpleRouter.

src/Pecee/Http/Middleware/BaseCsrfVerifier.php

@@ -0,0 +1,33 @@
+<?php
+
+namespace Pecee\Http\Middleware;
+
+use Pecee\CsrfToken;
+use Pecee\Http\Request;
+use Pecee\SimpleRouter\RouterException;
+
+class BaseCsrfVerifier extends Middleware {
+
+    const POST_KEY = 'csrf-token';
+    const HEADER_KEY = 'X-CSRF-TOKEN';
+
+    public function handle(Request $request) {
+
+        if($request->getMethod() != 'get') {
+
+            $token = (isset($_POST[self::POST_KEY])) ? $_POST[self::POST_KEY] : null;
+
+            // If the token is not posted, check headers for valid x-csrf-token
+            if($token === null) {
+                $token = $request->getHeader(self::HEADER_KEY);
+            }
+
+            $tokenValidator = new CsrfToken();
+            if( !$tokenValidator->validate( $token ) ) {
+                throw new RouterException('Invalid csrf-token.');
+            }
+
+        }
+
+    }
+}