I personally prefer to reserve the use of objects for times when the data structure needs to have methods associated with it as well. I like the simplicity of a dictionary for many cases.

That said, when there are a lot of places where the dictionary needs to be used, it can be difficult to have a central location to document what needs to be in the dictionary, and a class is a nice way to do that. In those instances, I think a class is better.

It seems that this is just an API thing - perhaps it could be adjusted to just accept a CA cert and an entitlement cert as separate parameters to the method. That way it's clear what they are for, and no "difficult to document" dictionary is involved.