signature/policy_config.go
func newPRSignedByKeyPath(keyType sbKeyType, keyPath string, signedIdentity PolicyReferenceMatch) (*prSignedBy, error) {
	return newPRSignedBy(keyType, keyPath, nil, signedIdentity)
}
func newPRSignedByKeyPath(keyType sbKeyType, keyPath string, signedIdentity PolicyReferenceMatch) (*prSignedBy, error) {
	return newPRSignedBy(keyType, keyPath, nil, signedIdentity)
}
// newPRSignedByKeyPath is NewPRSignedByKeyPath, except it returns the private type.