public JaasConfiguration(String principal,File keytab,String appName){
  this(principal,keytab,null,null);
  clientAppName=appName;
  serverAppName=null;
}

public JaasConfiguration ( String principal , File keytab , String appName ) { this ( principal , keytab , null , null ) ; clientAppName = appName ; serverAppName = null ; }
add an entry to the jaas configuration with the passed in principal and keytab , along with the app name .
