Using Cookies to implement a RememberMe functionality

Some web applications may need a "Remember Me" functionality. This means that, after a user login, user will have access from same machine to all its data even after session expired. This access will be possible until user does a logout.

If you are using Spring  and its login form, then you should use "Remember Me" functionality already implemented inside the framework.

Some web frameworks also offer a type of SignIn panel which already has "remember me" built-in.

But in case you have to implement "Remember Me" functionality by your own, this can be easily achieved using Cookies. Java has a Cookie class named javax.servlet.http.Cookie.

Algorithm is straight-forward:

1. your login panel must contain a "Remember Me" check
2. after a succesfull login with "Remember Me" check selected, you can create two cookies: one to keep the value for rememberMe and one to keep  a token which has to identify the logged user. For sake of security, this token must never contain user name or user password. The ideea is to   generate a random id as token value. And token value aside with user id must be saved in your storage (database)
3. whenever a login is needed, you have to look if there is any cookie saved by you, and if so and your "rememberMe" value is true, you can take the user from storage based on your token and do an automatic login.
4. when a logout is done, you have to delete the cookie that keeps the token

To add a cookie, you have to specify the maximum age of the cookie in seconds :

     HttpServletResponse servletResponse = ...;
     Cookie c = new Cookie(COOKIE_NAME, encodeString(uuid));
     c.setMaxAge(365 * 24 * 60 * 60); // one year
     servletResponse.addCookie(c);

     HttpServletRequest servletRequest = ...;
     HttpServletResponse servletResponse = ... ;
     Cookie[] cookies = servletRequest.getCookies();                
     for (int i = 0; i < cookies.length; i++) {
          Cookie c = cookies[i];            
          if (c.getName().equals(COOKIE_NAME)) {        
              c.setMaxAge(0);
              c.setValue(null);
              servletResponse.addCookie(c);    
          } 
     }