Altering authorization groups based on variables

I am using the authorization_maps_alter hook currently to change which AD groups I am authorizing users against based on a set of variables. This process is very confusing and obfuscated, what I really want is some kind of hook that I can just return which roles I want the user mapped to based on their groups. Instead, I have to alter the mapping (and, since the mapping can't be empty to start with, I have to have a 'dummy' value in there or else I get an error about an empty array...). Am I approaching this the right way?