Acegi security pluing tag with Grails

Here are the most common tags to use with the Acegi and Grails:

g:ifallgranted role="ROLE_ADMIN,ROLE_SUPERVISOR">
g:ifanygranted role="ROLE_ADMIN,ROLE_SUPERVISOR">
g:ifnotgranted role="ROLE_USER">
g:isloggedin>
g:isnotloggedin>

Also you can get some extra info about the logged in user/

g:loggedinuserinfo field="username"> // as a gtag
${loggedInUserInfo(field:'username')} // as a GString-expression

Getting the loggedin or current User
If you have the Grails/Acegi plugin installed

 def authenticateService

  def list = { 
     def user = authenticateService.principal() 
     def username = user?.getUsername()

If you don't have Acegi or Jsecurity plugin installed

        Object obj =
                SecurityContextHolder.getContext().getAuthentication().getPrincipal();
        String username;
        if ( obj instanceof UserDetails ) {
            username= ( (UserDetails)obj ).getUsername();
        } else {
        }