Getting MyBB to eat a Yummier Cookie?

[Firefox Wins]

Not sure if this belongs in Coding = Questions and issues related to coding (HTML/CSS/Javascript/PHP or Fortran),
or Modifications?

PHP Code:

if (secure_cookie_value = "Firefox Wins") {action = 'Let him into MyBB now!!' ; } // Yes, integration, SSO & security are advanced topics & that is OK.

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Please, point me in the right direction, and I can figure the rest out:
For simplicity: Assume account(s) are already created and secure login (setting a non-MyBB cookie) is done over SSL*
*Which might cause issues reading the secure cookie over plain http

How to:
Getting MyBB to eat a Yummier Cookie?
a) User already exists in the MyBB database.
b) "Secure cookie" is set and has built in protection against session hijacking.
c) I already know how to do an "SSO type" of auto-login using MyBB's functions, but then logout won't be based on "Secure cookie", it would be "a normal logout."
d) Where do I start to get MyBB to accept a replacement "Secure cookie" for login and logout?

I know sessions are stored in the db; What I'm looking to do is have "virtually everything else the same" , while MyBB accepts "Secure (outside) cookie" instead of the normal one.

Any tips on where to start?
Thank you, for helpful advice.