--- a/web/app/controllers.php
+++ b/web/app/controllers.php
@@ -58,14 +58,20 @@
     // processing the request
     if ($app['session']->has('username')) {
         $username = $app['session']->get('username');
-        $preferences = $app['preferences.repository']->userPreferences($username);
-        $app['user.preferences'] = $preferences;
-        $app['user.timezone'] = $preferences->get('timezone');
+        // Clear user session if HTTP authentication changed
+        if (isset($_SERVER['PHP_AUTH_USER'])
+        && $username != $_SERVER['PHP_AUTH_USER']) {
+            $app['session']->clear();
+        } else {
+            $preferences = $app['preferences.repository']->userPreferences($username);
+            $app['user.preferences'] = $preferences;
+            $app['user.timezone'] = $preferences->get('timezone');
 
-        // Set application language
-        $request->setLocale($preferences->get('language'));
-        $app['translator']->setLocale($preferences->get('language'));
-        return;
+            // Set application language
+            $request->setLocale($preferences->get('language'));
+            $app['translator']->setLocale($preferences->get('language'));
+            return;
+        }
     }
 
     if ($request->isXmlHttpRequest()) {
--- a/web/src/Controller/Authentication.php
+++ b/web/src/Controller/Authentication.php
@@ -34,7 +34,7 @@
         $success = false;
         $template_vars = [];
 
-        if ($request->isMethod('POST')) {
+        if ($request->isMethod('POST') || isset($_SERVER['PHP_AUTH_USER'])) {
             $user = $request->request->get('user');
             $password = $request->request->get('password');
 
@@ -93,8 +93,14 @@
             return false;
         }
 
-        $app['session']->set('username', $user);
-        $app['session']->set('password', $password);
+        if (isset($_SERVER['PHP_AUTH_USER']) && isset($_SERVER['PHP_AUTH_PW'])) {
+            $user = $_SERVER['PHP_AUTH_USER'];
+            $password = $_SERVER['PHP_AUTH_PW'];
+        } else {
+            $app['session']->set('username', $user);
+            $app['session']->set('password', $password);
+        }
+
         $principal_url = $caldav_client->getCurrentUserPrincipal();
 
         $principals_repository = $app['principals.repository'];