Enrolment

i have an external database we use for our own developed web app, i want to use the same database to Authencate and assign users to cohorts..

the authencation side i've done..  i have a column in the external db called "role_id_fk" its an INT format and goes from 1 - 6 ( 1 being staff, 2 being team leader and so on)  

i've tried asking on FB and googling but for the life of me no one can give me simple step by step instructions, or even tell me if its even possible.. 

Example

user = Becky
role_id_fk = 2

she would be entered into the cohort with the id = 2. doable?