AFAIK
Cookie Sharing
If all of your applications are on the intranet and are all made using the dot net stack. It makes sense to take advantage of the sharing cookies. I previously had success implementing SSO using this strategy where the main login would be an old web forms application and it would authorise a dotnet core app.
Pros: You are using the Microsoft stack, easy to setup.
Cons: You are locked to using the Microsoft stack. Falls over if you want to use with native/js applications.
IdentityServer4
Having experimented quite a bit with this library, this is an abstraction of the OAuth2 and OpenIdConnect protocols, essentially authentication and authorisation using jwt tokens. IdentityServer4 allows you to specify your authority (AS => Authentication Server) which is handles authenticating clients (your other applications be it .net, js or native). The token that the AS gives the clients are then used to determine if the client has access to the an API. You get to specify which clients can access which api's and how much of it can they access based on Claims. It is possible to convert Active Directory groups into claims and authorise by that level.
Pros: Really good abstraction they simplify a big part of the process. You can secure any type of client (js/native/.net).
Cons: You still have to learn OAuth2 & OpenIdConnect specs, which can take quite some time. You'll probably endup writing quite a bit of configuration depending on how big the network of apps that you are trying to secure.
JWT Middleware
This just allows the api to authorize tokens against an authority, and it doesn't really provide the "centralized authentication structure", you will have to handle alot of the flow setup your self. generally just a watered down version of IS4.
Pros: fast and simple way to secure an api to an already existing Authority.
Cons: Doesn't allow you to create a Authentication Server.
Summary
I'd say go with Cookie Sharing if you don't plan on securing native apps or js apps.
If you are setting up token based authentication read below.
Go with IdentityServer4 for long term flexible solution and if you have time to learn how to use it and set it up.
if you have an authority and don't mind doing a bit of setup go with JWT Middleware, this will be a bit more flexible than Cookie Sharing.
