How to Integrate CI Script Login with SMF?

It is possible to integrate website login from my main site(CodeIgniter Framework 2.x) to SMF 2.x? My main script is under domain name www.example.com and my SMF script is under subdomain forum.example.com. Now I want the user will not going to register or create another account for the Forum(SMF) when they already have an account on my main website.?

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