Supporting OAuth2 external user logins may be very useful for Enterprise customers. Because you know that now SSO(Single sing on) methods are moving through solutions like IdentityServer or Google Auth etc.using OAuth2. If I have an IdentityServer I do not need more. Windows Authentication solutions like LDAP are platform specific. But now we need platform indipended authentications.
I should be able to configure my Portal for ArcGIS or ArcGIS server using IdentityServer for my company.