JNDI authentication question

In my code, pasted below, I can get a list of users and their email addresses. I can paste this class into any code and it would get a list of users in a domain. What I DON'T want is for users to have to instantiate the ADConnection class with a username and password.

Is there a way to impersonate a currently logged on user using JNDI? Is there another way to do this?

public class ADConnection {

      private DirContext ldapContext;

      private String baseName;

      private String serverIP;

      private String user;

      private String passwd;

      public ADConnection(String baseDN, String serverIP, String user,
                  String passwd) {

            this.baseName = baseDN;
            this.serverIP = serverIP;
            this.user = user;
            this.passwd = passwd;

            try {
                  Hashtable ldapEnv = new Hashtable(11);

                  ldapEnv.put(Context.INITIAL_CONTEXT_FACTORY,
                              "com.sun.jndi.ldap.LdapCtxFactory");
                  ldapEnv.put(Context.PROVIDER_URL, "ldap://" + serverIP + ":389");
                  if (user != null) {
                        ldapEnv.put(Context.SECURITY_AUTHENTICATION, "simple");
                        ldapEnv.put(Context.SECURITY_PRINCIPAL, user);
                        ldapEnv.put(Context.SECURITY_CREDENTIALS, passwd);
                  }
                  ldapContext = new InitialDirContext(ldapEnv);
            } catch (Exception e) {
                  System.out.println(" bind error: " + e);
                  e.printStackTrace();
                  System.exit(-1);
            }
      }

      public NamingEnumeration search() {
            SearchControls ctls = new SearchControls();

            ctls.setReturningObjFlag(true);
            String filter = "(objectclass=*)";
            NamingEnumeration answer = null;
            try {
                  answer = ldapContext.search(baseName, filter, ctls);
            } catch (NamingException e) {
                  e.printStackTrace();
            }
            //printSearchEnumeration(answer);
            return answer;
      }

      public static void printSearchEnumeration(NamingEnumeration enum) {
            try {
                  while (enum.hasMore()) {
                        SearchResult sr = (SearchResult) enum.next();
                        Attributes attrib = sr.getAttributes();

                        System.out.println(sr.getName() + ": " + attrib.get("mail"));
                  }
            } catch (NamingException e) {
                  e.printStackTrace();
            }
      }

      public static void main(String[] args) {
            ADConnection adc = new ADConnection(
                        "ou=Users, ou=My Domain, dc=dc, dc=local", "domainC",
                        "test@dc.local", "Password123");
            NamingEnumeration searchResult;

            searchResult = adc.search();
            printSearchEnumeration(searchResult);
            System.out.println("done");
      }
}