在symfony2登录成功之后和重定向之前做一些事情？

I'm searching for a while now, for any info, on how to do something after authentication success in symfony2. I want to rehash user password to use bcrypt just after successful authentication using old hash. I need to do this when I still have valid plain password so it should be just after credentials check and before redirect. I'm searching for a while now, for any info, on