How to map additional claims in IdentityServer 4 and MVC .Net 461 framework

Question

We've been using Idsrv4 for about 2 years and we have successfully integrated with .Net Core Apis, .Net Core Apps. Now, we've got a legacy app which is costly to migrate to .Net Core from Net461.

I'm trying to integrate our .Net 461 MVC app with Identity Server 4 and I almost managed to integrate it successfully. But the issue is that, I don't know how to map non-standard claims to MVC App User Claims.

For example, in our claims, we've got special params like Country and custom_user_id. If I inspect the JwtAccessToken, I can see the values and I can confirm that the claims/scopes are working correct. But in UserClaims, they do not exist at all. I can only find the standard claims like sub, nbr, etc...

In .Net Core app, it's easy and we just need to use ClaimActions.MapUniqueJsonKey like following:

services.AddOpenIdConnect("oidc", options =>
                {
                    ....

                    options.ClaimActions.MapUniqueJsonKey(JwtClaimTypes.Role, JwtClaimTypes.Role);
                    options.ClaimActions.MapUniqueJsonKey(Constants.CustomClaimTypes.Country, Constants.CustomClaimTypes.Country);
                    options.ClaimActions.MapUniqueJsonKey("custom_user_id", "custom_user_id");
                    options.ClaimActions.MapUniqueJsonKey("custom_company_id", "custom_company_id");

Could you please guide me how can I force OWIN library to get data from UserInfoEndpoint and map our custom claims to UserClaims?

I'm using OWIN library and my OWIN StartUp class looks like the following:

public void Configuration(IAppBuilder app)
        {
            app.SetDefaultSignInAsAuthenticationType(CookieAuthenticationDefaults.AuthenticationType);

            app.UseCookieAuthentication(new CookieAuthenticationOptions());
            app.UseOpenIdConnectAuthentication(
                new OpenIdConnectAuthenticationOptions
                {
                    ClientId = xxxx,
                    ClientSecret = xxx,
                    Authority = Constants.Urls.IdentityServerProviderUrl,
                    ......
                    Scope = PopulateScopes(), // custom method
                    SignInAsAuthenticationType = CookieAuthenticationDefaults.AuthenticationType,
                    ResponseType = OpenIdConnectResponseType.Code,
                   
                    UseTokenLifetime = false,
                    RedeemCode = true,
                    SaveTokens = true,                    

                    TokenValidationParameters = new TokenValidationParameters()
                    {
                        ValidateIssuer = true                        
                    },
                }
            );                
        }