Grails SpringSecurityService: Authenticate via Code manually

Use case

After struggling around for more than one hour to find out a good practise to login a user within the springSecurity-architecture manually.
I found this helpfull post in the Grails user mailing list:
http://grails.1312388.n4.nabble.com/Automatically-logging-a-user-in-after-ajax-registration-with-Spring-Security-td3166809.html

Solution

// Find bu username
User user = User.findWhere( username: params.username )

// Check if passwords equal
if( user.password == springSecurityService.encodePassword( params.password ) ) {

  def request = RCH.currentRequestAttributes().currentRequest
  def response = RCH.currentRequestAttributes().currentResponse                

  // Get user details
  UserDetails userDetails = springSecurityService.getUserDetailsService().loadUserByUsername( params.username )

  // Build Token
  def authentication = new UsernamePasswordAuthenticationToken( userDetails, params.password )
  authentication.details = new WebAuthenticationDetails(request)
  SCH.context.authentication = authentication                

  // Do the authentication adn store in session (otherwise the user is only logged in for this request)
  request.session.setAttribute( AuthenticationProcessingFilter.SPRING_SECURITY_LAST_USERNAME_KEY, user.username )
  authenticationManager.authenticate( authentication )

  // optional remember me
  //rememberMeServices.loginSuccess request, response, authentication
}