programmatic login using spring security

[nambi]

I have a website that spring security for authentication.
It works fine.

When User registers the to site, I would like to login the user automatically to the website.
What is the best way to achieve this?

[Rob Winch]

The easiest way to log a user in is to set the Authentication on the SecurityContextHolder's context. For example:

Authentication authentication = new UsernamePasswordAuthenticationToken("username", "password",
                AuthorityUtils.createAuthorityList("ROLE_USER"));
SecurityContextHolder.getContext().setAuthentication(authentication);

Note that in many instances Spring Security uses a User object as the principal instead of "username". However, depending on your usecase "username" will work just fine.