How to implement SSO on subdomains?

Question

ASP.NET

There is one project consisting of several smaller projects. Each project is a web application, all hosted on different subdomains (eg auth.project.local, admin.project.local, portal.project.local etc.). The authorization project uses ASP.NET Identity. How to make it so that you can log in to auth.project.local once and authorization is no longer required for admin and portal. Tried to change cookieDomain - does not help.

app.UseCookieAuthentication(new CookieAuthenticationOptions
            {
                AuthenticationType = "ProjectCookie",
                LoginPath = new PathString("/"),
                CookieName = "AppSession",
                CookieDomain = ".project.local",
                Provider = new CookieAuthenticationProvider
                {
                    OnValidateIdentity = SecurityStampValidator.OnValidateIdentity<UserManager<User, long>, User, long>(
                        validateInterval: TimeSpan.FromMinutes(10),
                        regenerateIdentityCallback: (manager, user) => user.GenerateUserIdentityAsync(manager),
                        getUserIdCallback: id => id.GetUserId<long>()
                   )
                }

There is also one more question: how to make it so that on a subdomain, for example, portal.project.local, if the user is not authorized, a redirect to auth.project.local is carried out with a returnUrl referring to portal.project.local?

Answer 1

stackoverflow.com/questions/19166599/asp-net-ident...
Is the config the same everywhere?
Write the full path instead of / in the loginpaf, I myself have not tried it.