Sitecore 9.1 was released recently after the Sitecore Symposium 2018, and there are a lot of goodies to be found. Pieter Brinkman has a really good series on all the new features of Sitecore 9.1.
I want to add a little bit of addendum to my original post for all the Sitecore 9 Infrastructure roles. If you visited some of the technical talks at the Symposium, you’ll see a pattern towards breaking a monolithic architecture into a much more manageable micro component architecture. This means some of the functions from the main application will get split out. If you look at the recently updated documentation, you’ll find that there are now a LOT of infrastructure roles. Note – my earlier blog post only refers to application roles. You’ve already seen this initiative in the case of xConnect and the publishing service (and various other cases), which are both separate roles, and are slated to run independently of the main CM or CD instance.
Sitecore Identity Server
Sitecore 9.1 continues this trend, and introduces a new application role, called the Identity Server. The Identity Server is a separate ASP.NET Core application that manages the authentication for Sitecore. After installing 9.1, you’ll see that when you go to log into Sitecore CM, you’ll get redirected from https://{instanceName}/sitecore to https://{instanceName}-IdentityServer.
The beauty of this is that now authentication delegated into a separate role, and we can now use this role to set up SSO (Single Sign-On) across Sitecore services and applications. You can use the SI server is based on OpenID Connect-compliant security token service and can manage/update/refresh tokens. These tokens can then be used to manage authetication for Sitecore Services. This will also allow users to sign into various sites and services that are hosted separately even when you do not have a running instance of Sitecore XP.
Planning
From an infrastructure planning perspective, this is a minor change. If you’re on Azure, this is another app service. If you are on-premise, then this is another IIS Site. This can be scaled separately from the other roles if you plan to use it extensively. Otherwise, it has a pretty small footprint. This is a benefit of the split up from the monolithic architecture, otherwise, you would need to scale out the whole CM/CD role just to scale out maybe a single function.
All in all, I think this is a great direction for Sitecore to go into. Initially, it can be overwhelming, but once you understand the roles, it is much easier to manage.
The Runtime Report 