A person who cannot legally enter into a certain contract directly can do so indirectly through an agent.

Legally Enter

The act of gaining access or entry to a property, system, or situation in accordance with the law and authorized permissions.

Contract

A contract is a legally binding agreement between two or more parties that outlines obligations each party must perform.

Indirectly

In a manner that is not straightforward or direct; happening through secondary or alternative means or effects.