Entity Framework Core - realtion between two tables without using primary key

I would like to write Console application in dotnet core 2.1 with EFCore.Postgres 2.1.2.

I have two tables in existing Database. Every table has it's own Primary key, but these tables should be related via another field - UserId

My models:

public class UserAddress
{
    public int UserAddressId {get;set;}
    public int UserId {get;set;}
    public string City {get;set;}
    public string Street {get; set;}

    public virtual UserDetails UserDetails {get;set;}
}

public class UserDetails
{
    public int UserDetailId {get;set;}
    public int UserId {get;set;}

    public string Name {get;set;}
    public string Surname {get;set;}
}

How Can I 'Teach' Entityframework to join these tables wia UserId? I would like to use them like below

using (var MyDb = new GraffitiDbContext())
{
    var query = MyDb.UserAddress              
        .Include(row => row.UserDetails);

    foreach (var item in query)
    {
        Console.Writeline(item.UserDetails.Name);
    }
}