add support of refresh token

examples/TrackManiaAuthenticator.php

@@ -42,6 +42,11 @@ class TrackManiaAuthenticator extends OAuth2Authenticator
         $client = $this->clientRegistry->getClient('TrackMania');
         $accessToken = $this->fetchAccessToken($client);
 
+        // Store the refresh token in the session
+        if ($accessToken->getRefreshToken() !== null) {
+            $request->getSession()->set('oauth2_trackmania_accesstoken', $accessToken);
+        }
+
         $selfvalidating = new SelfValidatingPassport(
             new UserBadge($accessToken->getToken(), function() use ($accessToken, $client) {
                 /** @var Beu\TrackMania\OAuth2\Client\Provider\TrackManiaProviderOwner $user */