Startup.cs

public class Startup
{
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddIdentityServer()
            .AddDeveloperSigningCredential()
            .AddInMemoryApiResources(Configuration.ApiResources)
            .AddInMemoryClients(Configuration.Clients);
    }

    public void Configure(IApplicationBuilder app, IHostingEnvironment env)
    {
        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }

        app.UseIdentityServer();
    }
}