Update google.golang.org/genproto

vendor/google.golang.org/api/internal/cert/default_cert.go

@@ -0,0 +1,58 @@
+// Copyright 2020 Google LLC.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package cert contains certificate tools for Google API clients.
+// This package is intended to be used with crypto/tls.Config.GetClientCertificate.
+//
+// The certificates can be used to satisfy Google's Endpoint Validation.
+// See https://cloud.google.com/endpoint-verification/docs/overview
+//
+// This package is not intended for use by end developers. Use the
+// google.golang.org/api/option package to configure API clients.
+package cert
+
+import (
+	"crypto/tls"
+	"errors"
+	"sync"
+)
+
+// defaultCertData holds all the variables pertaining to
+// the default certficate source created by DefaultSource.
+//
+// A singleton model is used to allow the source to be reused
+// by the transport layer.
+type defaultCertData struct {
+	once   sync.Once
+	source Source
+	err    error
+}
+
+var (
+	defaultCert defaultCertData
+)
+
+// Source is a function that can be passed into crypto/tls.Config.GetClientCertificate.
+type Source func(*tls.CertificateRequestInfo) (*tls.Certificate, error)
+
+// errSourceUnavailable is a sentinel error to indicate certificate source is unavailable.
+var errSourceUnavailable = errors.New("certificate source is unavailable")
+
+// DefaultSource returns a certificate source using the preferred EnterpriseCertificateProxySource.
+// If EnterpriseCertificateProxySource is not available, fall back to the legacy SecureConnectSource.
+//
+// If neither source is available (due to missing configurations), a nil Source and a nil Error are
+// returned to indicate that a default certificate source is unavailable.
+func DefaultSource() (Source, error) {
+	defaultCert.once.Do(func() {
+		defaultCert.source, defaultCert.err = NewEnterpriseCertificateProxySource("")
+		if errors.Is(defaultCert.err, errSourceUnavailable) {
+			defaultCert.source, defaultCert.err = NewSecureConnectSource("")
+			if errors.Is(defaultCert.err, errSourceUnavailable) {
+				defaultCert.source, defaultCert.err = nil, nil
+			}
+		}
+	})
+	return defaultCert.source, defaultCert.err
+}