Infinite authentication loop when using identityserver4 in asp.net core 2.0

I also had a login loop after copying the startup code from an existing .NET Core 2.2 project and reused it in a new .NET Core 3.1 project.

The problem here was, that the app.UseAuthentication() must be called before the new app.UseAuthorization();

https://docs.microsoft.com/en-us/aspnet/core/migration/22-to-30?view=aspnetcore-3.1&tabs=visual-studio#migrate-startupconfigure

Only in case someone is running into this issue too...

Adding default Identity in the client app would cause an infinite redirect loop.

In the client app, if you need to use UserManager, RoleManager.

Then use the below code.

services.AddIdentityCore<IdentityUser>()
                .AddRoles<IdentityRole>()
                .AddRoleManager<RoleManager<IdentityRole>>()
                .AddSignInManager<SignInManager<IdentityUser>>()
                .AddEntityFrameworkStores<ApplicationDbContext>();

In your client app, in Startup check if you have something like

services.AddIdentity<ApplicationUser, IdentityRole>()
                .AddEntityFrameworkStores<ApplicationDbContext>()
                .AddDefaultTokenProviders();

Remove that part and try again.