diff --git a/README.md b/README.md
index 90e83a9..59acb3f 100644
--- a/README.md
+++ b/README.md
@@ -8,6 +8,8 @@ Also known as X.509 client authentication.
 3. This package allows `Admin` to use your app without ever logging in.
 4. All users including `Admin` can still use plain password auth.
 
+> __Pro tip__: you can also [use any other certificate attributes](https://github.com/ingria/laravel-x509-auth/wiki/Using-other-cert-attributes) for authentication, not only `emailAddress` (like `id` or `username`). I don't think you need this package in that case, but anyway 🤷.
+
 ## Prerequisites
 
 Please don't blindly copy-paste the commands. It's important for you to know what you're doing.
diff --git a/src/Middleware/AuthenticateWithClientCertificate.php b/src/Middleware/AuthenticateWithClientCertificate.php
index 6b7f59f..e739209 100644
--- a/src/Middleware/AuthenticateWithClientCertificate.php
+++ b/src/Middleware/AuthenticateWithClientCertificate.php
@@ -50,7 +50,7 @@ public function handle($request, Closure $next, $guard = null)
 
         /** If the certificate is valid, log in and remember the user: */
         if ($request->server('SSL_CLIENT_VERIFY') === 'SUCCESS') {
-            $this->auth->guard($guard)->login(self::getUserFromCert($request), true);
+            $this->auth->guard($guard)->login(static::getUserFromCert($request), true);
 
             return $next($request);
         }
@@ -65,7 +65,7 @@ public function handle($request, Closure $next, $guard = null)
      * @param  Request $request
      * @return App\User
      */
-    private static function getUserFromCert(Request $request)
+    protected static function getUserFromCert(Request $request)
     {
         /**
          * Probably misconfigured Nginx:
@@ -90,7 +90,7 @@ private static function getUserFromCert(Request $request)
      * @param  string $subject
      * @return string
      */
-    private static function getEmailFromDn(string $subject): string
+    protected static function getEmailFromDn(string $subject): string
     {
         preg_match('/emailAddress=([\w\+]+@[a-z\-\d]+\.[a-z\-\.\d]{2,})/i', $subject, $match);