String data   = request.getParameter("data");
String sign64 = request.getParameter("sign");
String clientip = request.getRemoteAddr();

// SSOclient is from SSOclient.java
SSOclient sso = new SSOclient(data, sign64, clientip, "targetname");
if(sso.oklogin()){
  out.println("You are logged in as :" + sso.loginvalues().get("username"));
} else {
  out.println("error: " + sso.reason());
}