Vendor in c/image with sigstore support

Signed-off-by: Miloslav Trmač <mitr@redhat.com>

vendor/github.com/letsencrypt/boulder/identifier/identifier.go

@@ -0,0 +1,32 @@
+// The identifier package defines types for RFC 8555 ACME identifiers.
+package identifier
+
+// IdentifierType is a named string type for registered ACME identifier types.
+// See https://tools.ietf.org/html/rfc8555#section-9.7.7
+type IdentifierType string
+
+const (
+	// DNS is specified in RFC 8555 for DNS type identifiers.
+	DNS = IdentifierType("dns")
+)
+
+// ACMEIdentifier is a struct encoding an identifier that can be validated. The
+// protocol allows for different types of identifier to be supported (DNS
+// names, IP addresses, etc.), but currently we only support RFC 8555 DNS type
+// identifiers for domain names.
+type ACMEIdentifier struct {
+	// Type is the registered IdentifierType of the identifier.
+	Type IdentifierType `json:"type"`
+	// Value is the value of the identifier. For a DNS type identifier it is
+	// a domain name.
+	Value string `json:"value"`
+}
+
+// DNSIdentifier is a convenience function for creating an ACMEIdentifier with
+// Type DNS for a given domain name.
+func DNSIdentifier(domain string) ACMEIdentifier {
+	return ACMEIdentifier{
+		Type:  DNS,
+		Value: domain,
+	}
+}