how to use roles framework without adding its tables to my databse

hi,
i want to implement role_based autherization in an application, the only way i know to do it is to use roles framework, but i don't want to add any extra tables to my database, my database already have a users table with a column that specifies a role for each user
how can i use this framework without adding the tables it requires to my database?
 
thanks.
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