Support webauthn (#17957)

Migrate from U2F to Webauthn

Co-authored-by: Andrew Thornton <art27@cantab.net>
Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

vendor/github.com/google/certificate-transparency-go/x509/nilref_nil_darwin.go

@@ -0,0 +1,26 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build cgo,!arm,!arm64,!ios,!go1.10
+
+package x509
+
+/*
+#cgo CFLAGS: -mmacosx-version-min=10.6 -D__MAC_OS_X_VERSION_MAX_ALLOWED=1080
+#cgo LDFLAGS: -framework CoreFoundation -framework Security
+
+#include <CoreFoundation/CoreFoundation.h>
+*/
+import "C"
+
+// For Go versions before 1.10, nil values for Apple's CoreFoundation
+// CF*Ref types were represented by nil.  See:
+//   https://github.com/golang/go/commit/b868616b63a8
+func setNilCFRef(v *C.CFDataRef) {
+	*v = nil
+}
+
+func isNilCFRef(v C.CFDataRef) bool {
+	return v == nil
+}