219 lines
6.3 KiB
Go
219 lines
6.3 KiB
Go
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package spnego
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import (
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"context"
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"encoding/binary"
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"encoding/hex"
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"errors"
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"fmt"
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"github.com/jcmturner/gofork/encoding/asn1"
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"github.com/jcmturner/gokrb5/v8/asn1tools"
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"github.com/jcmturner/gokrb5/v8/client"
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"github.com/jcmturner/gokrb5/v8/credentials"
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"github.com/jcmturner/gokrb5/v8/gssapi"
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"github.com/jcmturner/gokrb5/v8/iana/chksumtype"
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"github.com/jcmturner/gokrb5/v8/iana/msgtype"
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"github.com/jcmturner/gokrb5/v8/krberror"
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"github.com/jcmturner/gokrb5/v8/messages"
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"github.com/jcmturner/gokrb5/v8/service"
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"github.com/jcmturner/gokrb5/v8/types"
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)
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// GSSAPI KRB5 MechToken IDs.
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const (
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TOK_ID_KRB_AP_REQ = "0100"
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TOK_ID_KRB_AP_REP = "0200"
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TOK_ID_KRB_ERROR = "0300"
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)
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// KRB5Token context token implementation for GSSAPI.
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type KRB5Token struct {
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OID asn1.ObjectIdentifier
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tokID []byte
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APReq messages.APReq
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APRep messages.APRep
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KRBError messages.KRBError
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settings *service.Settings
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context context.Context
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}
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// Marshal a KRB5Token into a slice of bytes.
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func (m *KRB5Token) Marshal() ([]byte, error) {
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// Create the header
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b, _ := asn1.Marshal(m.OID)
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b = append(b, m.tokID...)
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var tb []byte
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var err error
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switch hex.EncodeToString(m.tokID) {
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case TOK_ID_KRB_AP_REQ:
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tb, err = m.APReq.Marshal()
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if err != nil {
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return []byte{}, fmt.Errorf("error marshalling AP_REQ for MechToken: %v", err)
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}
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case TOK_ID_KRB_AP_REP:
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return []byte{}, errors.New("marshal of AP_REP GSSAPI MechToken not supported by gokrb5")
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case TOK_ID_KRB_ERROR:
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return []byte{}, errors.New("marshal of KRB_ERROR GSSAPI MechToken not supported by gokrb5")
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}
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if err != nil {
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return []byte{}, fmt.Errorf("error mashalling kerberos message within mech token: %v", err)
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}
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b = append(b, tb...)
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return asn1tools.AddASNAppTag(b, 0), nil
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}
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// Unmarshal a KRB5Token.
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func (m *KRB5Token) Unmarshal(b []byte) error {
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var oid asn1.ObjectIdentifier
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r, err := asn1.UnmarshalWithParams(b, &oid, fmt.Sprintf("application,explicit,tag:%v", 0))
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if err != nil {
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return fmt.Errorf("error unmarshalling KRB5Token OID: %v", err)
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}
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if !oid.Equal(gssapi.OIDKRB5.OID()) {
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return fmt.Errorf("error unmarshalling KRB5Token, OID is %s not %s", oid.String(), gssapi.OIDKRB5.OID().String())
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}
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m.OID = oid
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if len(r) < 2 {
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return fmt.Errorf("krb5token too short")
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}
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m.tokID = r[0:2]
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switch hex.EncodeToString(m.tokID) {
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case TOK_ID_KRB_AP_REQ:
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var a messages.APReq
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err = a.Unmarshal(r[2:])
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if err != nil {
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return fmt.Errorf("error unmarshalling KRB5Token AP_REQ: %v", err)
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}
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m.APReq = a
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case TOK_ID_KRB_AP_REP:
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var a messages.APRep
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err = a.Unmarshal(r[2:])
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if err != nil {
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return fmt.Errorf("error unmarshalling KRB5Token AP_REP: %v", err)
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}
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m.APRep = a
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case TOK_ID_KRB_ERROR:
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var a messages.KRBError
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err = a.Unmarshal(r[2:])
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if err != nil {
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return fmt.Errorf("error unmarshalling KRB5Token KRBError: %v", err)
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}
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m.KRBError = a
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}
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return nil
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}
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// Verify a KRB5Token.
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func (m *KRB5Token) Verify() (bool, gssapi.Status) {
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switch hex.EncodeToString(m.tokID) {
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case TOK_ID_KRB_AP_REQ:
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ok, creds, err := service.VerifyAPREQ(&m.APReq, m.settings)
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if err != nil {
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return false, gssapi.Status{Code: gssapi.StatusDefectiveToken, Message: err.Error()}
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}
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if !ok {
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return false, gssapi.Status{Code: gssapi.StatusDefectiveCredential, Message: "KRB5_AP_REQ token not valid"}
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}
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m.context = context.Background()
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m.context = context.WithValue(m.context, ctxCredentials, creds)
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return true, gssapi.Status{Code: gssapi.StatusComplete}
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case TOK_ID_KRB_AP_REP:
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// Client side
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// TODO how to verify the AP_REP - not yet implemented
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return false, gssapi.Status{Code: gssapi.StatusFailure, Message: "verifying an AP_REP is not currently supported by gokrb5"}
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case TOK_ID_KRB_ERROR:
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if m.KRBError.MsgType != msgtype.KRB_ERROR {
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return false, gssapi.Status{Code: gssapi.StatusDefectiveToken, Message: "KRB5_Error token not valid"}
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}
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return true, gssapi.Status{Code: gssapi.StatusUnavailable}
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}
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return false, gssapi.Status{Code: gssapi.StatusDefectiveToken, Message: "unknown TOK_ID in KRB5 token"}
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}
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// IsAPReq tests if the MechToken contains an AP_REQ.
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func (m *KRB5Token) IsAPReq() bool {
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if hex.EncodeToString(m.tokID) == TOK_ID_KRB_AP_REQ {
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return true
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}
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return false
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}
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// IsAPRep tests if the MechToken contains an AP_REP.
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func (m *KRB5Token) IsAPRep() bool {
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if hex.EncodeToString(m.tokID) == TOK_ID_KRB_AP_REP {
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return true
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}
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return false
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}
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// IsKRBError tests if the MechToken contains an KRB_ERROR.
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func (m *KRB5Token) IsKRBError() bool {
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if hex.EncodeToString(m.tokID) == TOK_ID_KRB_ERROR {
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return true
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}
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return false
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}
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// Context returns the KRB5 token's context which will contain any verify user identity information.
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func (m *KRB5Token) Context() context.Context {
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return m.context
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}
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// NewKRB5TokenAPREQ creates a new KRB5 token with AP_REQ
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func NewKRB5TokenAPREQ(cl *client.Client, tkt messages.Ticket, sessionKey types.EncryptionKey, GSSAPIFlags []int, APOptions []int) (KRB5Token, error) {
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// TODO consider providing the SPN rather than the specific tkt and key and get these from the krb client.
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var m KRB5Token
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m.OID = gssapi.OIDKRB5.OID()
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tb, _ := hex.DecodeString(TOK_ID_KRB_AP_REQ)
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m.tokID = tb
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auth, err := krb5TokenAuthenticator(cl.Credentials, GSSAPIFlags)
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if err != nil {
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return m, err
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}
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APReq, err := messages.NewAPReq(
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tkt,
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sessionKey,
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auth,
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)
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if err != nil {
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return m, err
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}
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for _, o := range APOptions {
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types.SetFlag(&APReq.APOptions, o)
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}
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m.APReq = APReq
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return m, nil
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}
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// krb5TokenAuthenticator creates a new kerberos authenticator for kerberos MechToken
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func krb5TokenAuthenticator(creds *credentials.Credentials, flags []int) (types.Authenticator, error) {
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//RFC 4121 Section 4.1.1
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auth, err := types.NewAuthenticator(creds.Domain(), creds.CName())
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if err != nil {
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return auth, krberror.Errorf(err, krberror.KRBMsgError, "error generating new authenticator")
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}
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auth.Cksum = types.Checksum{
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CksumType: chksumtype.GSSAPI,
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Checksum: newAuthenticatorChksum(flags),
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}
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return auth, nil
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}
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// Create new authenticator checksum for kerberos MechToken
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func newAuthenticatorChksum(flags []int) []byte {
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a := make([]byte, 24)
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binary.LittleEndian.PutUint32(a[:4], 16)
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for _, i := range flags {
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if i == gssapi.ContextFlagDeleg {
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x := make([]byte, 28-len(a))
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a = append(a, x...)
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}
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f := binary.LittleEndian.Uint32(a[20:24])
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f |= uint32(i)
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binary.LittleEndian.PutUint32(a[20:24], f)
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}
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return a
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}
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