// AssumeRoleWithCertificate case, the "virtual" parent user is the value of the
// `Subject.CommonName` field. For the OIDC (without RoleARN) case the "virtual"
// parent is derived as a concatenation of the `sub` and `iss` fields. The
// policies applicable to the STS credential are associated with this "virtual"
// parent.
//
// When a policyName is given to this function, the policy association is