add refresh token method

Signed-off-by: Maurice Preuß (envoyr) <hello@envoyr.com>

src/Id/Concerns/ManagesUsers.php

@@ -46,6 +46,20 @@ trait ManagesUsers
         return $this->post('v1/users', $attributes);
     }
 
+    /**
+     * Refreshes the access token using the refresh token.
+     */
+    public function refreshToken(string $storedRefreshToken, string $scope = ''): Result
+    {
+        return $this->post('../oauth/token', [
+            'grant_type'    => 'refresh_token',
+            'refresh_token' => $storedRefreshToken,
+            'client_id'     => $this->clientId,
+            'client_secret' => $this->clientSecret,
+            'scope'         => $scope,
+        ]);
+    }
+
     /**
      * Checks if the given email exists.
      *