How can I use a foreign key from the AspnetUser table in clean architecture

[hanushi]

We are migrating our ASP.NET Core 3.1 project to ASP.NET Core 6.0 Web API (clean architecture).

In our old project, we use IdentityUser (which is not in clean architecture) like this:

old project - User.cs

public class User : IdentityUser
{
// removed
}
This is the table named as AspNetUser in the database.

Now, in our clean architecture project,

public class ApplicationUser : IdentityUser
{}

My issue is I want to use a foreign key from the AspnetUser table to another class.

public class SiteUsers
{
public int SiteCodeId { get; set; }
public SiteCode SiteCode { get; set; }
public string UserId { get; set; }
public ApplicationUser User { get; set; } // can not use ApplicationUser here. Then How can I use AspnetUser table inside Domain Layer.
}

Example: FK_SiteUsers_AspNetUsers_UserId.

ApplicationUser (which extends IdentityUser) is in the Infrastructure layer. Could not use this class into domain Layer in clean architecture

How can I use a foreign key from the AspnetUser table in Domain Layer? Please anyone help me. Thanks.