Hi, Kishore.
Can't say anything helpful yet. Just one moment: to modify Shibboleth's configuration (the package that responsible for serving SAML request in Gluu) you need to modify at least Velocity templates in `/opt/tomcat/conf/shibboleth2/idp/` directory (in your case it will be file `handler.xml.vm`). When tomcat is started, they are being used to deploy configuration files in the `/opt/idp/conf` directory, from where it is loaded by Shibboleth.
I'm not sure it's refreshing configuration after start, so to be sure changes are applied you should restart the tomcat service each time you modify anything in these directories. So it's quite possible that if you change just templates in `/opt/tomcat/conf/shibboleth2/idp/` and restart the service, then Shibboleth will load previous version of configuration (before tomcat will have a change to deploy updated files from templates); that's why it's better to modify files at both these directories at once, template and actual file (but be advised about significantly different syntaxes used in them!).
My current tests of using your approach are showing that even when correct configuration files are modified, it still won't work: for authentication it redirects me to the page at url like `https://my.host.name/idp/Authn/UserPassword` which has old-styled (2.3.x-like) design and looks somewhat broken; it doesn't allow you to log in (I'm attaching an error trace from idp-process.log)