PrivateCredentialPermission allows grants statements which have
a wildcard principalClass along with a regular principalName.

from a security point of view, this is a bad construct.
allowing any principal with the name "foo" (from any principalClass)
to access a private credential is not useful, and extremely risky
from a security perspective.

a wildcard principalClass AND wildcard principalName should be allowed.
a regular principalClass AND wildcard principalName should be allowed.

a wildcard principalClass AND regular principalName should NOT be allowed.