EJB-local lookup with user authentication

Hello!
We are migrating from JBoss 5 to JBoss 6.
We got a MDB that call's a EJB.
But in the EJB we check that the user got some roles.

In Jboss 5 we did
    private InitialContext getInitialContext(final String pProviderUrl, final String pPrinciple, final String pCredentials) throws NamingException {
          final Properties properties = new Properties();
          properties.put(Context.URL_PKG_PREFIXES, "org.jboss.naming:org.jnp.interfaces");
          properties.put(Context.PROVIDER_URL, pProviderUrl);
          if(pPrinciple != null && pCredentials != null) {
              properties.put(Context.INITIAL_CONTEXT_FACTORY, "org.jboss.security.jndi.JndiLoginInitialContextFactory");
              properties.put(Context.SECURITY_PRINCIPAL, pPrinciple);
              properties.put(Context.SECURITY_CREDENTIALS, pCredentials);
          }
          else {
              properties.put(Context.INITIAL_CONTEXT_FACTORY, "org.jnp.interfaces.NamingContextFactory");
          }
          return new InitialContext(properties);
    }
...then to roles was present.

But In Jboss 6 I can not find out how to do the same.
I found this clue:
https://developer.jboss.org/thread/202291
...but when I get to:
SecurityContextAssociation.setPrincipal and SecurityContextAssociation.setCredential
...the compiler says that the method is undefind:
The method setCredential(String) is undefined for the type SecurityContextAssociation

Do you guys got any idea how to solve this in Jboss 6?
Best regards
Fredrik