Fix url option key.

Closes #3845

src/Controller/Component/AuthComponent.php

@@ -710,7 +710,7 @@ class AuthComponent extends Component {
 			$redir = '/';
 		}
 		if (is_array($redir)) {
-			return Router::url($redir + array('base' => false));
+			return Router::url($redir + array('_base' => false));
 		}
 		return $redir;
 	}

tests/TestCase/Controller/Component/AuthComponentTest.php

@@ -1143,6 +1143,13 @@ class AuthComponentTest extends TestCase {
 		$result = $this->Auth->redirectUrl($value);
 		$this->assertEquals('/users/home', $result);
 		$this->assertEquals($value, $this->Auth->session->read('Auth.redirect'));
+
+		$request = new Request();
+		$request->base = '/base';
+		Router::setRequestInfo($request);
+
+		$result = $this->Auth->redirectUrl($value);
+		$this->assertEquals('/users/home', $result);
 	}
 
 /**