Add deep linking support for SAML

Deep linking allows instances to support direct email links to a particular record in the system.

With the SAML 2.0 integration enabled, deep-linking URLs must pass an authentication check before the IdP redirects the user to the originally requested URL. For example, consider an email that contains this URL: https://<instance name>.service-now.com/nav_to.do?uri=incident.do?sys_id=46c88ac1a9fe1981014de1c831fbcf6d

The instance sends an authentication request to the IdP and uses the RelayState URL parameter to preserve the originally requested resource (in this case, uri=incident.do?sys_id=46c88ac1a9fe1981014de1c831fbcf6d). After the IdP authenticates the user, the instance reads the value of the RelayState URL parameter and redirects the user to the requested resource (if it exists in the instance).

To add support for deep linking verify that the identity provider supports the RelayState URL parameter.