Want to save to my DB


Hi, first of all I am new to twitter auth.

I am have given option to the visitors of my site to login with twitter.
I want to save the oauth_token which is send back to me after login process to my DB. Reason is I do not want to create a new account every time user login with twitter. Next time user login with twitter I will check the returned oauth_token in my db and if exist I will not create new account.

Now I am worried because I am not sure if oauth_token expires or not.