vendor: add cfssl dependency

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

@@ -0,0 +1,37 @@
+// Copyright 2011 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 dragonfly freebsd linux openbsd netbsd
+
+package x509
+
+import "io/ioutil"
+
+// Possible certificate files; stop after finding one.
+var certFiles = []string{
+	"/etc/ssl/certs/ca-certificates.crt",     // Debian/Ubuntu/Gentoo etc.
+	"/etc/pki/tls/certs/ca-bundle.crt",       // Fedora/RHEL
+	"/etc/ssl/ca-bundle.pem",                 // OpenSUSE
+	"/etc/ssl/cert.pem",                      // OpenBSD
+	"/usr/local/share/certs/ca-root-nss.crt", // FreeBSD/DragonFly
+}
+
+func (c *Certificate) systemVerify(opts *VerifyOptions) (chains [][]*Certificate, err error) {
+	return nil, nil
+}
+
+func initSystemRoots() {
+	roots := NewCertPool()
+	for _, file := range certFiles {
+		data, err := ioutil.ReadFile(file)
+		if err == nil {
+			roots.AppendCertsFromPEM(data)
+			systemRoots = roots
+			return
+		}
+	}
+
+	// All of the files failed to load. systemRoots will be nil which will
+	// trigger a specific error at verification time.
+}