diff --git a/go/vendor/google.golang.org/grpc/credentials/credentials.go b/go/vendor/google.golang.org/grpc/credentials/credentials.go
new file mode 100644
index 0000000..6c2b811
--- /dev/null
+++ b/go/vendor/google.golang.org/grpc/credentials/credentials.go
@@ -0,0 +1,312 @@
+/*
+ *
+ * Copyright 2014 gRPC 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
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package credentials implements various credentials supported by gRPC library,
+// which encapsulate all the state needed by a client to authenticate with a
+// server and make various assertions, e.g., about the client's identity, role,
+// or whether it is authorized to make a particular call.
+package credentials // import "google.golang.org/grpc/credentials"
+
+import (
+	"crypto/tls"
+	"crypto/x509"
+	"errors"
+	"fmt"
+	"io/ioutil"
+	"net"
+	"strings"
+
+	"github.com/golang/protobuf/proto"
+	"golang.org/x/net/context"
+)
+
+// alpnProtoStr are the specified application level protocols for gRPC.
+var alpnProtoStr = []string{"h2"}
+
+// PerRPCCredentials defines the common interface for the credentials which need to
+// attach security information to every RPC (e.g., oauth2).
+type PerRPCCredentials interface {
+	// GetRequestMetadata gets the current request metadata, refreshing
+	// tokens if required. This should be called by the transport layer on
+	// each request, and the data should be populated in headers or other
+	// context. If a status code is returned, it will be used as the status
+	// for the RPC. uri is the URI of the entry point for the request.
+	// When supported by the underlying implementation, ctx can be used for
+	// timeout and cancellation.
+	// TODO(zhaoq): Define the set of the qualified keys instead of leaving
+	// it as an arbitrary string.
+	GetRequestMetadata(ctx context.Context, uri ...string) (map[string]string, error)
+	// RequireTransportSecurity indicates whether the credentials requires
+	// transport security.
+	RequireTransportSecurity() bool
+}
+
+// ProtocolInfo provides information regarding the gRPC wire protocol version,
+// security protocol, security protocol version in use, server name, etc.
+type ProtocolInfo struct {
+	// ProtocolVersion is the gRPC wire protocol version.
+	ProtocolVersion string
+	// SecurityProtocol is the security protocol in use.
+	SecurityProtocol string
+	// SecurityVersion is the security protocol version.
+	SecurityVersion string
+	// ServerName is the user-configured server name.
+	ServerName string
+}
+
+// AuthInfo defines the common interface for the auth information the users are interested in.
+type AuthInfo interface {
+	AuthType() string
+}
+
+// ErrConnDispatched indicates that rawConn has been dispatched out of gRPC
+// and the caller should not close rawConn.
+var ErrConnDispatched = errors.New("credentials: rawConn is dispatched out of gRPC")
+
+// TransportCredentials defines the common interface for all the live gRPC wire
+// protocols and supported transport security protocols (e.g., TLS, SSL).
+type TransportCredentials interface {
+	// ClientHandshake does the authentication handshake specified by the corresponding
+	// authentication protocol on rawConn for clients. It returns the authenticated
+	// connection and the corresponding auth information about the connection.
+	// Implementations must use the provided context to implement timely cancellation.
+	// gRPC will try to reconnect if the error returned is a temporary error
+	// (io.EOF, context.DeadlineExceeded or err.Temporary() == true).
+	// If the returned error is a wrapper error, implementations should make sure that
+	// the error implements Temporary() to have the correct retry behaviors.
+	//
+	// If the returned net.Conn is closed, it MUST close the net.Conn provided.
+	ClientHandshake(context.Context, string, net.Conn) (net.Conn, AuthInfo, error)
+	// ServerHandshake does the authentication handshake for servers. It returns
+	// the authenticated connection and the corresponding auth information about
+	// the connection.
+	//
+	// If the returned net.Conn is closed, it MUST close the net.Conn provided.
+	ServerHandshake(net.Conn) (net.Conn, AuthInfo, error)
+	// Info provides the ProtocolInfo of this TransportCredentials.
+	Info() ProtocolInfo
+	// Clone makes a copy of this TransportCredentials.
+	Clone() TransportCredentials
+	// OverrideServerName overrides the server name used to verify the hostname on the returned certificates from the server.
+	// gRPC internals also use it to override the virtual hosting name if it is set.
+	// It must be called before dialing. Currently, this is only used by grpclb.
+	OverrideServerName(string) error
+}
+
+// Bundle is a combination of TransportCredentials and PerRPCCredentials.
+//
+// It also contains a mode switching method, so it can be used as a combination
+// of different credential policies.
+//
+// Bundle cannot be used together with individual TransportCredentials.
+// PerRPCCredentials from Bundle will be appended to other PerRPCCredentials.
+//
+// This API is experimental.
+type Bundle interface {
+	TransportCredentials() TransportCredentials
+	PerRPCCredentials() PerRPCCredentials
+	// NewWithMode should make a copy of Bundle, and switch mode. Modifying the
+	// existing Bundle may cause races.
+	//
+	// NewWithMode returns nil if the requested mode is not supported.
+	NewWithMode(mode string) (Bundle, error)
+}
+
+// TLSInfo contains the auth information for a TLS authenticated connection.
+// It implements the AuthInfo interface.
+type TLSInfo struct {
+	State tls.ConnectionState
+}
+
+// AuthType returns the type of TLSInfo as a string.
+func (t TLSInfo) AuthType() string {
+	return "tls"
+}
+
+// GetChannelzSecurityValue returns security info requested by channelz.
+func (t TLSInfo) GetChannelzSecurityValue() ChannelzSecurityValue {
+	v := &TLSChannelzSecurityValue{
+		StandardName: cipherSuiteLookup[t.State.CipherSuite],
+	}
+	// Currently there's no way to get LocalCertificate info from tls package.
+	if len(t.State.PeerCertificates) > 0 {
+		v.RemoteCertificate = t.State.PeerCertificates[0].Raw
+	}
+	return v
+}
+
+// tlsCreds is the credentials required for authenticating a connection using TLS.
+type tlsCreds struct {
+	// TLS configuration
+	config *tls.Config
+}
+
+func (c tlsCreds) Info() ProtocolInfo {
+	return ProtocolInfo{
+		SecurityProtocol: "tls",
+		SecurityVersion:  "1.2",
+		ServerName:       c.config.ServerName,
+	}
+}
+
+func (c *tlsCreds) ClientHandshake(ctx context.Context, authority string, rawConn net.Conn) (_ net.Conn, _ AuthInfo, err error) {
+	// use local cfg to avoid clobbering ServerName if using multiple endpoints
+	cfg := cloneTLSConfig(c.config)
+	if cfg.ServerName == "" {
+		colonPos := strings.LastIndex(authority, ":")
+		if colonPos == -1 {
+			colonPos = len(authority)
+		}
+		cfg.ServerName = authority[:colonPos]
+	}
+	conn := tls.Client(rawConn, cfg)
+	errChannel := make(chan error, 1)
+	go func() {
+		errChannel <- conn.Handshake()
+	}()
+	select {
+	case err := <-errChannel:
+		if err != nil {
+			return nil, nil, err
+		}
+	case <-ctx.Done():
+		return nil, nil, ctx.Err()
+	}
+	return tlsConn{Conn: conn, rawConn: rawConn}, TLSInfo{conn.ConnectionState()}, nil
+}
+
+func (c *tlsCreds) ServerHandshake(rawConn net.Conn) (net.Conn, AuthInfo, error) {
+	conn := tls.Server(rawConn, c.config)
+	if err := conn.Handshake(); err != nil {
+		return nil, nil, err
+	}
+	return tlsConn{Conn: conn, rawConn: rawConn}, TLSInfo{conn.ConnectionState()}, nil
+}
+
+func (c *tlsCreds) Clone() TransportCredentials {
+	return NewTLS(c.config)
+}
+
+func (c *tlsCreds) OverrideServerName(serverNameOverride string) error {
+	c.config.ServerName = serverNameOverride
+	return nil
+}
+
+// NewTLS uses c to construct a TransportCredentials based on TLS.
+func NewTLS(c *tls.Config) TransportCredentials {
+	tc := &tlsCreds{cloneTLSConfig(c)}
+	tc.config.NextProtos = alpnProtoStr
+	return tc
+}
+
+// NewClientTLSFromCert constructs TLS credentials from the input certificate for client.
+// serverNameOverride is for testing only. If set to a non empty string,
+// it will override the virtual host name of authority (e.g. :authority header field) in requests.
+func NewClientTLSFromCert(cp *x509.CertPool, serverNameOverride string) TransportCredentials {
+	return NewTLS(&tls.Config{ServerName: serverNameOverride, RootCAs: cp})
+}
+
+// NewClientTLSFromFile constructs TLS credentials from the input certificate file for client.
+// serverNameOverride is for testing only. If set to a non empty string,
+// it will override the virtual host name of authority (e.g. :authority header field) in requests.
+func NewClientTLSFromFile(certFile, serverNameOverride string) (TransportCredentials, error) {
+	b, err := ioutil.ReadFile(certFile)
+	if err != nil {
+		return nil, err
+	}
+	cp := x509.NewCertPool()
+	if !cp.AppendCertsFromPEM(b) {
+		return nil, fmt.Errorf("credentials: failed to append certificates")
+	}
+	return NewTLS(&tls.Config{ServerName: serverNameOverride, RootCAs: cp}), nil
+}
+
+// NewServerTLSFromCert constructs TLS credentials from the input certificate for server.
+func NewServerTLSFromCert(cert *tls.Certificate) TransportCredentials {
+	return NewTLS(&tls.Config{Certificates: []tls.Certificate{*cert}})
+}
+
+// NewServerTLSFromFile constructs TLS credentials from the input certificate file and key
+// file for server.
+func NewServerTLSFromFile(certFile, keyFile string) (TransportCredentials, error) {
+	cert, err := tls.LoadX509KeyPair(certFile, keyFile)
+	if err != nil {
+		return nil, err
+	}
+	return NewTLS(&tls.Config{Certificates: []tls.Certificate{cert}}), nil
+}
+
+// ChannelzSecurityInfo defines the interface that security protocols should implement
+// in order to provide security info to channelz.
+type ChannelzSecurityInfo interface {
+	GetSecurityValue() ChannelzSecurityValue
+}
+
+// ChannelzSecurityValue defines the interface that GetSecurityValue() return value
+// should satisfy. This interface should only be satisfied by *TLSChannelzSecurityValue
+// and *OtherChannelzSecurityValue.
+type ChannelzSecurityValue interface {
+	isChannelzSecurityValue()
+}
+
+// TLSChannelzSecurityValue defines the struct that TLS protocol should return
+// from GetSecurityValue(), containing security info like cipher and certificate used.
+type TLSChannelzSecurityValue struct {
+	StandardName      string
+	LocalCertificate  []byte
+	RemoteCertificate []byte
+}
+
+func (*TLSChannelzSecurityValue) isChannelzSecurityValue() {}
+
+// OtherChannelzSecurityValue defines the struct that non-TLS protocol should return
+// from GetSecurityValue(), which contains protocol specific security info. Note
+// the Value field will be sent to users of channelz requesting channel info, and
+// thus sensitive info should better be avoided.
+type OtherChannelzSecurityValue struct {
+	Name  string
+	Value proto.Message
+}
+
+func (*OtherChannelzSecurityValue) isChannelzSecurityValue() {}
+
+type tlsConn struct {
+	*tls.Conn
+	rawConn net.Conn
+}
+
+var cipherSuiteLookup = map[uint16]string{
+	tls.TLS_RSA_WITH_RC4_128_SHA:                "TLS_RSA_WITH_RC4_128_SHA",
+	tls.TLS_RSA_WITH_3DES_EDE_CBC_SHA:           "TLS_RSA_WITH_3DES_EDE_CBC_SHA",
+	tls.TLS_RSA_WITH_AES_128_CBC_SHA:            "TLS_RSA_WITH_AES_128_CBC_SHA",
+	tls.TLS_RSA_WITH_AES_256_CBC_SHA:            "TLS_RSA_WITH_AES_256_CBC_SHA",
+	tls.TLS_RSA_WITH_AES_128_GCM_SHA256:         "TLS_RSA_WITH_AES_128_GCM_SHA256",
+	tls.TLS_RSA_WITH_AES_256_GCM_SHA384:         "TLS_RSA_WITH_AES_256_GCM_SHA384",
+	tls.TLS_ECDHE_ECDSA_WITH_RC4_128_SHA:        "TLS_ECDHE_ECDSA_WITH_RC4_128_SHA",
+	tls.TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA:    "TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA",
+	tls.TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA:    "TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA",
+	tls.TLS_ECDHE_RSA_WITH_RC4_128_SHA:          "TLS_ECDHE_RSA_WITH_RC4_128_SHA",
+	tls.TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA:     "TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA",
+	tls.TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA:      "TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA",
+	tls.TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA:      "TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA",
+	tls.TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256:   "TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256",
+	tls.TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256: "TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256",
+	tls.TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384:   "TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384",
+	tls.TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384: "TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384",
+	tls.TLS_FALLBACK_SCSV:                       "TLS_FALLBACK_SCSV",
+}