Proof of Control is a MAY be a form of Proof of Ownership; which might be inappropriate.
LDAPWiki believes Credentials should never be shared.
Credential sharing presents a problem with Assurance of the trustworthiness
The owner of a Digital Identity MAY use Delegation to allow another entity to perform some functions but Credential use is not one of those functions. If this action is required, then a revocable of a Derived Credential should be utilized.