HttpCookie to Session Cookie

Would like to convert the following lines of code:

private const string USERCOOKIENAME = "mysite.user";

protected virtual HttpCookie GetUserCookie()
{
    if (_httpContext == null || _httpContext.Request == null)
        return null;
    return _httpContext.Request.Cookies[USERCOOKIENAME];
}

protected virtual void SetUserCookie(Guid userGuid)
{
    if (_httpContext != null || _httpContext.Response != null)
    {
        var cookie = new HttpCookie(USERCOOKIENAME);
        cookie.HttpOnly = true;
        cookie.Value = userGuid.ToString();

        if (userGuid == Guid.Empty)
        {
            cookie.Expires = DateTime.Now.AddMonths(-1);
        }
        else
        {
            int cookieExpires = 24 * 365;
            cookie.Expires = DateTime.Now.AddHours(cookieExpires);
        }

        _httpContext.Response.Cookies.Remove(USERCOOKIENAME);
        _httpContext.Response.Cookies.Add(cookie);
    }
}

I already have this in my Startup.cs

            app.UseCookieAuthentication(new CookieAuthenticationOptions
            {
                LoginPath = "/Login",
                AccessDeniedPath = "/Error",
                AuthenticationScheme = "Cookies",
                AutomaticAuthenticate = true,
                AutomaticChallenge = true
            });

I use my own Users/Roles tables.