Problem on SSO Login

yes I have to enable login required for disallowed anonymous access.
I am explaining again
The following flow is executed for my website when I enable SSO login and set everything up for SSO login

  1. this is my main website. here a one community button ,when user click this button it will call forum.mywebsite.com/login

  2. forum.mywebsite.com/login call my community(discourse community) website login page. then user who logged in main website is automatically logged as in community website(when I disabled login required setting of community website). But problem is that when I enable login required then login page does not call automatically. I have to click login button manually then It will logged the community page.

So I need some way to call the login button(or page) automatically without disabling login required settings.

This is official SSO Documentation link