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krb5.go
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krb5.go
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// Copyright 2023 jim.zoumo@gmail.com
//
// 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 krb5
import (
"encoding/binary"
"fmt"
"strings"
"github.com/jcmturner/gokrb5/v8/client"
"github.com/jcmturner/gokrb5/v8/config"
"github.com/jcmturner/gokrb5/v8/credentials"
"github.com/jcmturner/gokrb5/v8/crypto"
"github.com/jcmturner/gokrb5/v8/gssapi"
"github.com/jcmturner/gokrb5/v8/iana/chksumtype"
"github.com/jcmturner/gokrb5/v8/iana/flags"
"github.com/jcmturner/gokrb5/v8/messages"
"github.com/jcmturner/gokrb5/v8/spnego"
"github.com/jcmturner/gokrb5/v8/types"
"github.com/pkg/errors"
"golang.org/x/crypto/ssh"
)
const (
ContextFlagREADY = 128
)
func NewGSSAPIClientWithCCache(krb5confPath, ccachePath string) (ssh.GSSAPIClient, error) {
cfg, err := config.Load(krb5confPath)
if err != nil {
return nil, err
}
cache, err := credentials.LoadCCache(ccachePath)
if err != nil {
return nil, err
}
client, err := client.NewFromCCache(cache, cfg)
if err != nil {
return nil, err
}
return newGSSAPIClient(client)
}
func NewGSSAPIClientWithPassword(krb5confPath, username, realm, password string) (ssh.GSSAPIClient, error) {
cfg, err := config.Load(krb5confPath)
if err != nil {
return nil, err
}
client := client.NewWithPassword(username, realm, password, cfg)
return newGSSAPIClient(client)
}
func newGSSAPIClient(client *client.Client) (ssh.GSSAPIClient, error) {
err := client.Login()
if err != nil {
return nil, errors.Wrap(err, "failed to login kerberos")
}
err = client.AffirmLogin()
if err != nil {
return nil, errors.Wrap(err, "failed to affirmLogin kerberos")
}
return &GSSAPIClient{
client: client,
}, nil
}
type GSSAPIClient struct {
client *client.Client
subkey types.EncryptionKey
}
// Create new authenticator checksum for kerberos MechToken
func (k *GSSAPIClient) newAuthenticatorChksum(flags []int) []byte {
a := make([]byte, 24)
binary.LittleEndian.PutUint32(a[:4], 16)
for _, i := range flags {
if i == gssapi.ContextFlagDeleg {
x := make([]byte, 28-len(a))
a = append(a, x...)
}
f := binary.LittleEndian.Uint32(a[20:24])
f |= uint32(i)
binary.LittleEndian.PutUint32(a[20:24], f)
}
return a
}
func (k *GSSAPIClient) InitSecContext(target string, token []byte, isGSSDelegCreds bool) ([]byte, bool, error) {
GSSAPIFlags := []int{
ContextFlagREADY,
gssapi.ContextFlagInteg,
gssapi.ContextFlagMutual,
}
if isGSSDelegCreds {
GSSAPIFlags = append(GSSAPIFlags, gssapi.ContextFlagDeleg)
}
APOptions := []int{flags.APOptionMutualRequired}
if len(token) == 0 {
newTarget := strings.ReplaceAll(target, "@", "/")
tkt, sKey, err := k.client.GetServiceTicket(newTarget)
if err != nil {
return nil, false, errors.Wrap(err, "failed to get service ticket")
}
krb5Token, err := spnego.NewKRB5TokenAPREQ(k.client, tkt, sKey, GSSAPIFlags, APOptions) //nolint
creds := k.client.Credentials
auth, err := types.NewAuthenticator(creds.Domain(), creds.CName())
if err != nil {
return nil, false, errors.Wrap(err, "failed to generate new authenticator")
}
auth.Cksum = types.Checksum{
CksumType: chksumtype.GSSAPI,
Checksum: k.newAuthenticatorChksum(GSSAPIFlags),
}
etype, _ := crypto.GetEtype(sKey.KeyType)
if err := auth.GenerateSeqNumberAndSubKey(sKey.KeyType, etype.GetKeyByteSize()); err != nil {
return nil, false, errors.Wrap(err, "failed to generate seq number and sub key")
}
k.subkey = auth.SubKey
apReq, err := messages.NewAPReq(tkt, sKey, auth)
if err != nil {
return nil, false, errors.Wrap(err, "failed to create NewAPReq")
}
for _, o := range APOptions {
types.SetFlag(&apReq.APOptions, o)
}
krb5Token.APReq = apReq
outToken, err := krb5Token.Marshal()
if err != nil {
return nil, false, errors.Wrap(err, "failed to marshal krb5 token")
}
return outToken, true, nil
}
var krb5Token spnego.KRB5Token
if err := krb5Token.Unmarshal(token); err != nil {
err := errors.Wrap(err, "unmarshal APRep token failed")
return nil, false, err
}
if krb5Token.IsKRBError() {
return nil, false, fmt.Errorf("received Kerberos error")
}
return nil, false, nil
}
func (k *GSSAPIClient) GetMIC(micFiled []byte) ([]byte, error) {
micToken, err := gssapi.NewInitiatorMICToken(micFiled, k.subkey)
if err != nil {
return nil, err
}
token, err := micToken.Marshal()
if err != nil {
return nil, err
}
return token, nil
}
func (k *GSSAPIClient) DeleteSecContext() error {
// k.client.Destroy()
return nil
}