As we can say principal for user/group/role, is there a common word for person/company/organization?
The word you are looking for is party.
I am taking a wild guess that you are trying to find an economy related term.
How about (economic) "entity"?
In my databases this is known as a legal entity (i.e. anything that can be bound by a contract). Typically, there are 4 main 'types'; Person, Company, Organization, Government
In most contexts, legal person explicitly includes companies and the like.