public static function generateAccessToken($clientID)
 {
     $refresh = new Token();
     $refresh->code = static::generateEntropy();
     $refresh->type = 2;
     $refresh->client_id = $clientID;
     $refresh->expiry = time() + Config::get("oauth2-sp::oauth2.access_lifetime");
     $refresh->save();
     $r = new Token();
     $r->code = static::generateEntropy();
     $r->type = 1;
     $r->client_id = $clientID;
     $r->refresh = $refresh->code;
     $r->expiry = time() + Config::get("oauth2-sp::oauth2.access_lifetime");
     $r->save();
     return $r;
 }