Creating session not working

I'm following this code here. First I tried to create session with the following code from createuser.json.jsp which is running on author instance and its working fine -

<%@include file="/libs/foundation/global.jsp"%>
<%@ page import="org.apache.sling.jcr.api.SlingRepository" %>
<%@ page import="com.day.cq.security.UserManager" %>
<%@ page import="com.day.cq.security.UserManagerFactory" %>
<%@ page import="com.day.cq.security.User" %>
<%@ page import="com.day.cq.security.Authorizable" %>
<%@ page import="com.day.cq.security.profile.Profile" %>
<%@ page import="java.util.Iterator" %>
<%@ page import="java.util.List" %>
<%@ page import="java.util.ArrayList" %>
<%@ page import="javax.jcr.Repository" %>
<%@ page import="javax.jcr.Session" %>
<%@ page import="javax.jcr.SimpleCredentials" %>
<%@ page import="org.apache.jackrabbit.commons.JcrUtils" %>
<%@ page import="org.apache.sling.commons.json.io.*" %><%

final SlingRepository repos = sling.getService(SlingRepository.class);

final UserManagerFactory umFactory = sling.getService(UserManagerFactory.class);
 
Session session = null;

try{
session = repos.loginAdministrative(null); // I'm able to create session
  
catch (Exception e)
{

   System.out.println("Exception Occured: " + e.getMessage());
}
finally
{
    session.logout(); 
    session = null;
}%>

but above code for creating session does not work on publish instance. So, I modified the code as below and tried to run on author instance but in this case createuser.json.jsp is not called. I do not see Sysout statement that I added -

<%@include file="/libs/foundation/global.jsp"%>
<%@ page import="org.apache.sling.jcr.api.SlingRepository" %>
<%@ page import="com.day.cq.security.UserManager" %>
<%@ page import="com.day.cq.security.UserManagerFactory" %>
<%@ page import="com.day.cq.security.User" %>
<%@ page import="com.day.cq.security.Authorizable" %>
<%@ page import="com.day.cq.security.profile.Profile" %>
<%@ page import="java.util.Iterator" %>
<%@ page import="java.util.List" %>
<%@ page import="java.util.ArrayList" %>
<%@ page import="javax.jcr.Repository" %>
<%@ page import="javax.jcr.Session" %>
<%@ page import="javax.jcr.SimpleCredentials" %>
<%@ page import="org.apache.jackrabbit.commons.JcrUtils" %>
<%@ page import="org.apache.sling.commons.json.io.*" %><%
final SlingRepository repos = sling.getService(SlingRepository.class);
final UserManagerFactory umFactory = sling.getService(UserManagerFactory.class);

try
{ System.out.println("Hello session creating");
Repository repository = JcrUtils.getRepository("http://host:4502/crx");
            Session session = repository.login(new SimpleCredentials("admin", "admin".toCharArray()),"crx.default"); 
       System.out.println("session: " + session);
  catch (Exception e)

{

   System.out.println("Exception Occured: " + e.getMessage());
}
finally
{
    session.logout(); 
    session = null;
}%>

Please let me know whats wrong I'm doing here. Appreciate your help.

Regards,

Sam