Custom URL redirects to Default URL after login

[StandardSanders]

We're on Tokyo and I followed the following two articles:

Custom URLs association to your instance (servicenow.com)
Generate SP metadata for SAML/SSO custom URL installations (servicenow.com)

Our SSO is Azure AD and we're using Domain Separation. 

When I go to our custom URL it successfully pulls the portal up with the custom URL. https://support.customurl.com/sp

It prompts me to login, when I do it reverts back to the default URL
https://<instance>.service-now.com/sp 

Our requirement for our newest client is to have it white labelled so that wherever they are in the portal the custom URL will appear.

We do have an SPEntryPage script that redirects based on role, wondering if that may have something to do with it.

/** 
 *
 *  Service Portal sample script include to indicate 
 *  1. which login page should be used
 *  2. the starting page after the user is authenticated 
 * 
 *  Script is configured using system properties
 
 *  PROPERTY                        VALUE
 *  glide.entry.page.script         new SPEntryPage().getLoginURL(); 
 *  glide.entry.first.page.script   new SPEntryPage().getFirstPageURL();
 * 
 * functions can return a path or null if no overrides are necessary
 * 
 **/
var SPEntryPage = Class.create();

SPEntryPage.prototype = {
	
	initialize: function() {
		this.logVariables = false;  // for debugging 
		var comp = gs.getUser().getCompanyID();
		
		if(comp) {
			var getSuffix = new GlideRecord('core_company');
			getSuffix.get(comp);
			
			this.portal = (getSuffix.u_portal.url_suffix) ? '/' + getSuffix.u_portal.url_suffix + '/' : '/ossp/';
		
		}
		else 
			this.portal = "/login_locate_sso.do";
		
		//this.portal = "/ossp/";      // The URL suffix specified in the sp_portal record
	},

	/***
	 *
	 * Referred to by property: glide.entry.page.script
	 * 
	 **/
	getLoginURL: function() {
		// When requesting a page directly (eg: /problem_list.do)
		// The platform session_timeout.do sets the login page to welcome.do
		// Since we are handling the login, clear that value
		var session = gs.getSession();
		var nt = session.getProperty("nav_to");
		var sPage = session.getProperty("starting_page");
		if (nt == "welcome.do")
			session.clearProperty("nav_to");
		
		if (!sPage && !nt)
			session.putProperty("starting_page", gs.getProperty("glide.login.home"));
		
		// Send the user to the portal's login page
		var portalGR = new GlideRecord("sp_portal");
		portalGR.addQuery("url_suffix", this.portal.replace(/\//g, ""));
		portalGR.addNotNullQuery("login_page");
		portalGR.query();
		if (portalGR.next())
			return this.portal + "?id=" + portalGR.login_page.id;

		// Send to the a default login page
		return this.portal + "?id=login";
	},
	
	/***
	 *
	 * Referred to by property: glide.entry.first.page.script
	 * 
	 **/
	getFirstPageURL: function() {
		var session = gs.getSession();
		this.logProperties('before', session);

		//has roles and is not a Service Portal page - go to UI16
		var nt = session.getProperty("nav_to");
		var isServicePortalURL = new GlideSPScriptable().isServicePortalURL(nt);
		var redirectURL = session.getProperty("login_redirect");

		//if (user.hasRoles() && !redirectURL && !isServicePortalURL)
			//return;
		if (user.hasRole("admin") && !redirectURL && !isServicePortalURL)
			return;
				if (user.hasRole("knowledge_admin") && !redirectURL && !isServicePortalURL)
			return;
						if (user.hasRole("report_admin") && !redirectURL && !isServicePortalURL)
			return;
								if (user.hasRole("problem_admin") && !redirectURL && !isServicePortalURL)
			return;
										if (user.hasRole("itil") && !redirectURL && !isServicePortalURL)
			return;
												if (user.hasRole("approver_user") && !redirectURL && !isServicePortalURL)
			return;


		// user may have logged in from a frame, the /login_redirect.do page will bust out of it
		if (!redirectURL) {
			// redirectURL is nav_to 
			// if nav_to == "welcome.do" then use starting_page
			var sPage = session.getProperty("starting_page");
			if (sPage && nt == "welcome.do")
				nt = sPage;
			
			// Avoid a redirect loop to the home page
			var ep = gs.getProperty("glide.login.home");
			if (nt) {
				if (ep == nt)
					nt = null;
			}
			 // PRB726860: if page is still welcome.do, go to glide.login.home preserving frameset
			if (nt == "welcome.do") {
				session.putProperty("nav_to", ep);
				return;
			}
			
			session.putProperty("login_redirect", nt || "true");
			return "/login_redirect.do?sysparm_stack=no";
		}

		session.clearProperty("login_redirect");
		session.clearProperty("nav_to");
		var returnUrl = this.portal;
		if (redirectURL && redirectURL != "true") {
			var spUrl = new GlideSPScriptable().mapUrlToSPUrl(redirectURL);
			returnUrl = spUrl ? this.portal + "?" + spUrl : redirectURL;
		}

		this.logProperties('after', session);
		if (!this.logVariables) {
			gs.log('redirectURL: ' + redirectURL);
			gs.log('User: ' + user.getName());
			gs.log('is internal: ' + (!user.hasRoles()));
			gs.log('returnUrl: ' + returnUrl);
		}

		return returnUrl;
	},

	logProperties: function(beforeOrAfter, session) {
		if (!this.logVariables)
			return; 
		
		gs.log('SPEntryPage: Redirect ------------------------------- ' + beforeOrAfter);
		gs.log('session.starting_page: ' + session.getProperty("starting_page"));
		gs.log('session.nav_to: ' + session.getProperty("nav_to"));
		gs.log('session.login_redirect: ' + session.getProperty("login_redirect"));
		gs.log('gs.fURI: ' + session.getURI());
	},
	
	type: 'SPEntryPage'
};

Is this how Custom URLs are supposed to operate? 
If so, what could I be missing?

Edit: 
It looks like this is only the SSO accounts that is doing this redirect. 
Do I need to set up a separate IDP in the instance for the CustomURL?

Thanks,
Mike

[Dishtiwari]

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