Thanks for feedback Sudharsan. However, as mentioned in my question, I am aware of these scripts in the Installation Exist group. These scripts are not used in the SSO customization properties configuration form.

I've tested disabling External Authentication and enabling within the SSO form "Enable external authentication" and providing a HTTP header name and ServiceNow field name and it works.

What I am attempting to do is parse the HTTP header value but I cannot seem to locate where the Single Sign-on script is located.