public class ApplicationUser : IdentityUser
    {
    }

   public class ApplicationRole : IdentityRole
{
    public ApplicationRole() : base() { }

    //
    public virtual List<RolePermission> Permissions {get;set;}
}

public class Permission
    {
    public int Id { get; set; }
    public string Name { get; set; }
    public virtual List<RolePermission> Roles { get; set; }
    }

protected override void OnModelCreating(ModelBuilder builder)
        {
            base.OnModelCreating(builder);
            // Customize the ASP.NET Identity model and override the defaults if needed.
            // For example, you can rename the ASP.NET Identity table names and more.
            // Add your customizations after calling base.OnModelCreating(builder);

    builder.Entity<Permission>()
            .ToTable("AspNetPermissions")
            .HasKey(x => x.Id);


builder.Entity<ApplicationRole>()
        .ToTable("AspNetRoles")
            .HasKey(x => x.Id);


builder.Entity<RolePermission>()
            .HasKey(x => new { x.RoleId, x.PermisionId });



builder.Entity<RolePermission>()
            .HasOne(x => x.Role)
            .WithMany(y => y.Permissions)
            .HasForeignKey(y => y.RoleId);

builder.Entity<RolePermission>()
            .HasOne(x => x.Permission)
            .WithMany(y => y.Roles) //Aconselho renomear a propriedade para RolePermissions na classe Permission
            .HasForeignKey(y => y.PermisionId);
        }


    }