FormsAuthentication.RedirectFromLoginPage is Ok but need to refresh page

[researchyar]

Hi all
I have setup Power BI Custom Security on the server.
When the system reaches the following line of code

FormsAuthentication.SetAuthCookie(@"administrator", false);

I get authenticated, but nothing special happens in Power BI on Iframe in my c# portal. in addition to

FormsAuthentication.RedirectFromLoginPage(@"administrator", false);

I tried but both need to refresh the page once to display the report. The next time it is refreshed, the Power BI report will be easily loaded on the screen It means that I am authenticated.

Maybe you can help me to solve my problem