Authenticating against Active Directory with Java on Linux

import com.sun.jndi.ldap.LdapCtxFactory;
import java.util.ArrayList;
import java.util.Hashtable;
import java.util.List;
import java.util.Iterator;
import javax.naming.Context;
import javax.naming.AuthenticationException;
import javax.naming.NamingEnumeration;
import javax.naming.NamingException;
import javax.naming.directory.Attribute;
import javax.naming.directory.Attributes;
import javax.naming.directory.DirContext;
import javax.naming.directory.SearchControls;
import javax.naming.directory.SearchResult;
import static javax.naming.directory.SearchControls.SUBTREE_SCOPE;

//import org.acegisecurity.AuthenticationException;
import org.acegisecurity.BadCredentialsException;
import org.acegisecurity.GrantedAuthority;
import org.acegisecurity.GrantedAuthorityImpl;
import org.acegisecurity.providers.AuthenticationProvider;
import org.acegisecurity.providers.UsernamePasswordAuthenticationToken;
import org.acegisecurity.providers.dao.AbstractUserDetailsAuthenticationProvider;
import org.acegisecurity.userdetails.UserDetails;
import org.acegisecurity.userdetails.UserDetailsService;
import org.acegisecurity.userdetails.UsernameNotFoundException;


class App2 {

public static void main(String[] args) {

    if (args.length != 4 && args.length != 2) {
    	System.out.println("Purpose: authenticate user against Active Directory and list group membership.");
    	System.out.println("Usage: App2 <username> <password> <domain> <server>");
    	System.out.println("Short usage: App2 <username> <password>");
    	System.out.println("(short usage assumes 'xyz.tld' as domain and 'abc' as server)");
    	System.exit(1);
    }

    String domainName;
    String serverName;

    if (args.length == 4)
    {
            domainName = args[2];
    	serverName = args[3];
    }
    else
    {
    	domainName = "xyz.tld";
    	serverName = "abc";
    }

        String username = args[0];
        String password = args[1];

    System.out.println("Authenticating " + username + "@" + domainName + " through " + serverName + "." + domainName);

        // bind by using the specified username/password
        Hashtable props = new Hashtable();
        String principalName = username + "@" + domainName;
        props.put(Context.SECURITY_PRINCIPAL, principalName);
        props.put(Context.SECURITY_CREDENTIALS, password);
        DirContext context;

        try {
            context = LdapCtxFactory.getLdapCtxInstance("ldap://" + serverName + "." + domainName + '/', props);
        System.out.println("Authentication succeeded!");

            // locate this user's record
            SearchControls controls = new SearchControls();
            controls.setSearchScope(SUBTREE_SCOPE);
            NamingEnumeration<SearchResult> renum = context.search(toDC(domainName),"(& (userPrincipalName="+principalName+")(objectClass=user))", controls);
            if(!renum.hasMore()) {
    	System.out.println("Cannot locate user information for " + username);
    	System.exit(1);
        }
            SearchResult result = renum.next();

            List<GrantedAuthority> groups = new ArrayList<GrantedAuthority>();
            Attribute memberOf = result.getAttributes().get("memberOf");
            if(memberOf!=null) {// null if this user belongs to no group at all
                for(int i=0; i<memberOf.size(); i++) {
                    Attributes atts = context.getAttributes(memberOf.get(i).toString(), new String[]{"CN"});
                    Attribute att = atts.get("CN");
                    groups.add(new GrantedAuthorityImpl(att.get().toString()));
                }
            }

            context.close();

        System.out.println();
        System.out.println("User belongs to: ");
        Iterator ig = groups.iterator();
        while (ig.hasNext()) {
    	System.out.println("   " + ig.next().toString());
        }

        } catch (AuthenticationException a) {
            System.out.println("Authentication failed: " + a);
            System.exit(1);
        } catch (NamingException e) {
            System.out.println("Failed to bind to LDAP / get account information: " + e);
            System.exit(1);
        }
   }

    private static String toDC(String domainName) {
        StringBuilder buf = new StringBuilder();
        for (String token : domainName.split("\.")) {
            if(token.length()==0)   continue;   // defensive check
            if(buf.length()>0)  buf.append(",");
            buf.append("DC=").append(token);
        }
        return buf.toString();
    }

}

LDAPConnection connection = new LDAPConnection( new LDAPJSSEStartTLSFactory() );
connection.connect(hostname, port);
connection.startTLS();
connection.bind(LDAPConnection.LDAP_V3, username+"@"+domain, password.getBytes());