Help requested: Auto entry into usergroup from fieldX profile entry

[makaiguy]

[Edited to simplify request]

I've searched but not found anything similar. Maybe I just wasn't creative enough in my search terms.

I would like to restrict entry to a given forum to those that have a particular value entered in a custom field in their profiles. I've created the field in the profile and also added a new vBphrase in which I can store the required value.

Would appreciate any guidance on how to accomplish this. I see two possibilities:

1. Each time the user enters the board, his fieldx value is compared to the reference vBphrase value, and if they match, he is automatically put into a special usergroup created for the purpose. If the fieldx value doesn't match the reference value, he is not put in/removed from the special usergroup. Then I can just use standard usergroup permissions to allow entry to the forum.
2. Some custom code entered into the section that grants forum access. Pseudocode would look something like

   if [(requesting specified conference number)
      and (fieldx doesn't match required value)]
   then (deny access)
   end if

Method "a" would be preferable because there may be some other permissions that could be added later and easily managed by this usergroup, but if method "b" is all anyone can help with, I'll gratefully take that too.

Any suggestions on how to do this?