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// Copyright 2019 The etcd Authors
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.
// Package credentials implements gRPC credential interface with etcd specific logic.
// e.g., client handshake with custom authority parameter
package credentials
import (
grpccredentials ""
// Config defines gRPC credential configuration.
type Config struct {
TLSConfig *tls.Config
// Bundle defines gRPC credential interface.
type Bundle interface {
UpdateAuthToken(token string)
// NewBundle constructs a new gRPC credential bundle.
func NewBundle(cfg Config) Bundle {
return &bundle{
tc: newTransportCredential(cfg.TLSConfig),
rc: newPerRPCCredential(),
// bundle implements "grpccredentials.Bundle" interface.
type bundle struct {
tc *transportCredential
rc *perRPCCredential
func (b *bundle) TransportCredentials() grpccredentials.TransportCredentials {
func (b *bundle) PerRPCCredentials() grpccredentials.PerRPCCredentials {
return b.rc
func (b *bundle) NewWithMode(mode string) (grpccredentials.Bundle, error) {
// no-op
return nil, nil
// transportCredential implements "grpccredentials.TransportCredentials" interface.
// transportCredential wraps TransportCredentials to track which
// addresses are dialed for which endpoints, and then sets the authority when checking the endpoint's cert to the
// hostname or IP of the dialed endpoint.
// This is a workaround of a gRPC load balancer issue. gRPC uses the dialed target's service name as the authority when
// checking all endpoint certs, which does not work for etcd servers using their hostname or IP as the Subject Alternative Name
// in their TLS certs.
// To enable, include both WithTransportCredentials(creds) and WithContextDialer(creds.Dialer)
// when dialing.
type transportCredential struct {
gtc grpccredentials.TransportCredentials
mu sync.Mutex
// addrToEndpoint maps from the connection addresses that are dialed to the hostname or IP of the
// endpoint provided to the dialer when dialing
addrToEndpoint map[string]string
func newTransportCredential(cfg *tls.Config) *transportCredential {
return &transportCredential{
gtc: grpccredentials.NewTLS(cfg),
addrToEndpoint: map[string]string{},
func (tc *transportCredential) ClientHandshake(ctx context.Context, authority string, rawConn net.Conn) (net.Conn, grpccredentials.AuthInfo, error) {
// Set the authority when checking the endpoint's cert to the hostname or IP of the dialed endpoint
dialEp, ok := tc.addrToEndpoint[rawConn.RemoteAddr().String()]
if ok {
_, host, _ := endpoint.ParseEndpoint(dialEp)
authority = host
return tc.gtc.ClientHandshake(ctx, authority, rawConn)
// return true if given string is an IP.
func isIP(ep string) bool {
return net.ParseIP(ep) != nil
func (tc *transportCredential) ServerHandshake(rawConn net.Conn) (net.Conn, grpccredentials.AuthInfo, error) {
return tc.gtc.ServerHandshake(rawConn)
func (tc *transportCredential) Info() grpccredentials.ProtocolInfo {
return tc.gtc.Info()
func (tc *transportCredential) Clone() grpccredentials.TransportCredentials {
copy := map[string]string{}
for k, v := range tc.addrToEndpoint {
copy[k] = v
return &transportCredential{
gtc: tc.gtc.Clone(),
addrToEndpoint: copy,
func (tc *transportCredential) OverrideServerName(serverNameOverride string) error {
return tc.gtc.OverrideServerName(serverNameOverride)
func (tc *transportCredential) Dialer(ctx context.Context, dialEp string) (net.Conn, error) {
// Keep track of which addresses are dialed for which endpoints
conn, err := endpoint.Dialer(ctx, dialEp)
if conn != nil {
tc.addrToEndpoint[conn.RemoteAddr().String()] = dialEp
return conn, err
// perRPCCredential implements "grpccredentials.PerRPCCredentials" interface.
type perRPCCredential struct {
authToken string
authTokenMu sync.RWMutex
func newPerRPCCredential() *perRPCCredential { return &perRPCCredential{} }
func (rc *perRPCCredential) RequireTransportSecurity() bool { return false }
func (rc *perRPCCredential) GetRequestMetadata(ctx context.Context, s ...string) (map[string]string, error) {
authToken := rc.authToken
return map[string]string{rpctypes.TokenFieldNameGRPC: authToken}, nil
func (b *bundle) UpdateAuthToken(token string) {
if b.rc == nil {
func (rc *perRPCCredential) UpdateAuthToken(token string) {
rc.authToken = token