Custom visuals not showing with Custom authentication

jubinsoni​ 

For you many thanks for pointing me the right way.  To anyone else stuck in the same hole:

The answer is to add two more parameters onto the definition of the sqlAuthCookie in webconfig.config thus:

    <authentication mode="Forms">
      <forms loginUrl="logon.aspx" name="sqlAuthCookie" timeout="60" path="/" cookieSameSite="None" requireSSL="true">
      </forms>
    </authentication>

and to add a line to mark the cookie secure in logon.aspx.cs in AllowInReader thus:

                if (passwordVerified)
                {
                    HttpCookie cookie = FormsAuthentication.GetAuthCookie(sUserName, false);
                    cookie.Secure = true;

                    FormsAuthentication.RedirectFromLoginPage(
                        sUserName, false);
                }
                else
                {
                    this.BtnLogon.Text = "Failed";
                    Response.Redirect("logon.aspx");
                }

I hope this saves someone else having to read as much contradictory Microsoft documentation as I had to!

Chris