PHPBB Add User Automatically When They Sign-up on the Main Website

I have a website that requires login and I’ve installed PHPBB to a subdomain. I want users to automatically register to the PHPBB forum when they register to the main page and I need to give them access to only specific forums so I need to give them forum permissions based on their choices on the register page. How can I achieve this?

I’ve tried sending requests to ACP Add User Plugin using cURL but it requires tokens so after some time token expires and I can’t send any more requests.