Add support for SSPI GSSAPI SASL mechanism bind (#402)

* Add support for SSPI GSSAPI SASL mechanism bind This change allows Windows clients to use current process' credentials for bind authentication. Co-authored-by: Filip Björck <[email protected]>
go-ldap · Dec 12, 2022 · 0e43630 · 0e43630
1 parent 360012b
commit 0e43630
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Showing 10 changed files with 884 additions and 34 deletions.
diff --git a/bind.go b/bind.go
@@ -558,3 +558,179 @@ func (l *Conn) NTLMChallengeBind(ntlmBindRequest *NTLMBindRequest) (*NTLMBindRes
 	err = GetLDAPError(packet)
 	return result, err
 }
+
+// GSSAPIClient interface is used as the client-side implementation for the
+// GSSAPI SASL mechanism.
+// Interface inspired by GSSAPIClient from golang.org/x/crypto/ssh
+type GSSAPIClient interface {
+	// InitSecContext initiates the establishment of a security context for
+	// GSS-API between the client and server.
+	// Initially the token parameter should be specified as nil.
+	// The routine may return a outputToken which should be transferred to
+	// the server, where the server will present it to AcceptSecContext.
+	// If no token need be sent, InitSecContext will indicate this by setting
+	// needContinue to false. To complete the context
+	// establishment, one or more reply tokens may be required from the server;
+	// if so, InitSecContext will return a needContinue which is true.
+	// In this case, InitSecContext should be called again when the
+	// reply token is received from the server, passing the reply token
+	// to InitSecContext via the token parameters.
+	// See RFC 4752 section 3.1.
+	InitSecContext(target string, token []byte) (outputToken []byte, needContinue bool, err error)
+	// NegotiateSaslAuth performs the last step of the Sasl handshake.
+	// It takes a token, which, when unwrapped, describes the servers supported
+	// security layers (first octet) and maximum receive buffer (remaining
+	// three octets).
+	// If the received token is unacceptable an error must be returned to abort
+	// the handshake.
+	// Outputs a signed token describing the client's selected security layer
+	// and receive buffer size and optionally an authorization identity.
+	// The returned token will be sent to the server and the handshake considered
+	// completed successfully and the server authenticated.
+	// See RFC 4752 section 3.1.
+	NegotiateSaslAuth(token []byte, authzid string) ([]byte, error)
+	// DeleteSecContext destroys any established secure context.
+	DeleteSecContext() error
+}
+
+// GSSAPIBindRequest represents a GSSAPI SASL mechanism bind request.
+// See rfc4752 and rfc4513 section 5.2.1.2.
+type GSSAPIBindRequest struct {
+	// Service Principal Name user for the service ticket. Eg. "ldap/<host>"
+	ServicePrincipalName string
+	// (Optional) Authorization entity
+	AuthZID string
+	// (Optional) Controls to send with the bind request
+	Controls []Control
+}
+
+// GSSAPIBind performs the GSSAPI SASL bind using the provided GSSAPI client.
+func (l *Conn) GSSAPIBind(client GSSAPIClient, servicePrincipal, authzid string) error {
+	return l.GSSAPIBindRequest(client, &GSSAPIBindRequest{
+		ServicePrincipalName: servicePrincipal,
+		AuthZID:              authzid,
+	})
+}
+
+// GSSAPIBindRequest performs the GSSAPI SASL bind using the provided GSSAPI client.
+func (l *Conn) GSSAPIBindRequest(client GSSAPIClient, req *GSSAPIBindRequest) error {
+	// nolint:errcheck
+	defer client.DeleteSecContext()
+
+	var err error
+	var reqToken []byte
+	var recvToken []byte
+	needInit := true
+	for {
+		if needInit {
+			// Establish secure context between client and server.
+			reqToken, needInit, err = client.InitSecContext(req.ServicePrincipalName, recvToken)
+			if err != nil {
+				return err
+			}
+		} else {
+			// Secure context is set up, perform the last step of SASL handshake.
+			reqToken, err = client.NegotiateSaslAuth(recvToken, req.AuthZID)
+			if err != nil {
+				return err
+			}
+		}
+		// Send Bind request containing the current token and extract the
+		// token sent by server.
+		recvToken, err = l.saslBindTokenExchange(req.Controls, reqToken)
+		if err != nil {
+			return err
+		}
+
+		if !needInit && len(recvToken) == 0 {
+			break
+		}
+	}
+
+	return nil
+}
+
+func (l *Conn) saslBindTokenExchange(reqControls []Control, reqToken []byte) ([]byte, error) {
+
+	// Construct LDAP Bind request with GSSAPI SASL mechanism.
+	envelope := ber.Encode(ber.ClassUniversal, ber.TypeConstructed, ber.TagSequence, nil, "LDAP Request")
+	envelope.AppendChild(ber.NewInteger(ber.ClassUniversal, ber.TypePrimitive, ber.TagInteger, l.nextMessageID(), "MessageID"))
+
+	request := ber.Encode(ber.ClassApplication, ber.TypeConstructed, ApplicationBindRequest, nil, "Bind Request")
+	request.AppendChild(ber.NewInteger(ber.ClassUniversal, ber.TypePrimitive, ber.TagInteger, 3, "Version"))
+	request.AppendChild(ber.NewString(ber.ClassUniversal, ber.TypePrimitive, ber.TagOctetString, "", "User Name"))
+
+	auth := ber.Encode(ber.ClassContext, ber.TypeConstructed, 3, "", "authentication")
+	auth.AppendChild(ber.NewString(ber.ClassUniversal, ber.TypePrimitive, ber.TagOctetString, "GSSAPI", "SASL Mech"))
+	if len(reqToken) > 0 {
+		auth.AppendChild(ber.NewString(ber.ClassUniversal, ber.TypePrimitive, ber.TagOctetString, string(reqToken), "Credentials"))
+	}
+	request.AppendChild(auth)
+	envelope.AppendChild(request)
+	if len(reqControls) > 0 {
+		envelope.AppendChild(encodeControls(reqControls))
+	}
+
+	msgCtx, err := l.sendMessage(envelope)
+	if err != nil {
+		return nil, err
+	}
+	defer l.finishMessage(msgCtx)
+
+	packet, err := l.readPacket(msgCtx)
+	if err != nil {
+		return nil, err
+	}
+	l.Debug.Printf("%d: got response %p", msgCtx.id, packet)
+	if l.Debug {
+		if err = addLDAPDescriptions(packet); err != nil {
+			return nil, err
+		}
+		ber.PrintPacket(packet)
+	}
+
+	// https://www.rfc-editor.org/rfc/rfc4511#section-4.1.1
+	// packet is an envelope
+	// child 0 is message id
+	// child 1 is protocolOp
+	if len(packet.Children) != 2 {
+		return nil, fmt.Errorf("bad bind response")
+	}
+
+	protocolOp := packet.Children[1]
+RESP:
+	switch protocolOp.Description {
+	case "Bind Response": // Bind Response
+		// Bind Reponse is an LDAP Response (https://www.rfc-editor.org/rfc/rfc4511#section-4.1.9)
+		// with an additional optional serverSaslCreds string (https://www.rfc-editor.org/rfc/rfc4511#section-4.2.2)
+		// child 0 is resultCode
+		resultCode := protocolOp.Children[0]
+		if resultCode.Tag != ber.TagEnumerated {
+			break RESP
+		}
+		switch resultCode.Value.(int64) {
+		case 14: // Sasl bind in progress
+			if len(protocolOp.Children) < 3 {
+				break RESP
+			}
+			referral := protocolOp.Children[3]
+			switch referral.Description {
+			case "Referral":
+				if referral.ClassType != ber.ClassContext || referral.Tag != ber.TagObjectDescriptor {
+					break RESP
+				}
+				return ioutil.ReadAll(referral.Data)
+			}
+			// Optional:
+			//if len(protocolOp.Children) == 4 {
+			//	serverSaslCreds := protocolOp.Children[4]
+			//}
+		case 0: // Success - Bind OK.
+			// SASL layer in effect (if any) (See https://www.rfc-editor.org/rfc/rfc4513#section-5.2.1.4)
+			// NOTE: SASL security layers are not supported currently.
+			return nil, nil
+		}
+	}
+
+	return nil, GetLDAPError(packet)
+}
diff --git a/examples_windows_test.go b/examples_windows_test.go
@@ -0,0 +1,36 @@
+//go:build windows
+// +build windows
+
+package ldap
+
+import (
+	"log"
+
+	"github.com/go-ldap/ldap/gssapi"
+)
+
+// This example demonstrates passwordless bind using the current process' user
+// credentials on Windows (SASL GSSAPI mechanism bind with SSPI client).
+func ExampleConn_SSPIClient_GSSAPIBind() {
+
+	// Windows only: Create a GSSAPIClient using Windows built-in SSPI lib
+	// (secur32.dll).
+	// This will use the credentials of the current process' user.
+	sspiClient, err := gssapi.NewSSPIClient()
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer sspiClient.Close()
+
+	l, err := DialURL("ldap://ldap.example.com:389")
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer l.Close()
+
+	// Bind using supplied GSSAPIClient implementation
+	err = l.GSSAPIBind(sspiClient, "ldap/ldap.example.com", "")
+	if err != nil {
+		log.Fatal(err)
+	}
+}
diff --git a/go.mod b/go.mod
@@ -4,7 +4,8 @@ go 1.14
 
 require (
 	github.com/Azure/go-ntlmssp v0.0.0-20220621081337-cb9428e4ac1e
+	github.com/alexbrainman/sspi v0.0.0-20210105120005-909beea2cc74
 	github.com/go-asn1-ber/asn1-ber v1.5.4
-	github.com/stretchr/testify v1.7.2 // indirect
-	golang.org/x/crypto v0.0.0-20220622213112-05595931fe9d // indirect
+	github.com/stretchr/testify v1.8.0
+	golang.org/x/crypto v0.1.0 // indirect
 )
diff --git a/go.sum b/go.sum
@@ -1,30 +1,50 @@
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-github.com/Azure/go-ntlmssp v0.0.0-20200615164410-66371956d46c/go.mod h1:chxPXzSsl7ZWRAuOIE23GDNzjWuZquvFlgA8xmpunjU=
-github.com/Azure/go-ntlmssp v0.0.0-20211209120228-48547f28849e h1:ZU22z/2YRFLyf/P4ZwUYSdNCWsMEI0VeyrFoI2rAhJQ=
-github.com/Azure/go-ntlmssp v0.0.0-20211209120228-48547f28849e/go.mod h1:chxPXzSsl7ZWRAuOIE23GDNzjWuZquvFlgA8xmpunjU=
 github.com/Azure/go-ntlmssp v0.0.0-20220621081337-cb9428e4ac1e h1:NeAW1fUYUEWhft7pkxDf6WoUvEZJ/uOKsvtpjLnn8MU=
 github.com/Azure/go-ntlmssp v0.0.0-20220621081337-cb9428e4ac1e/go.mod h1:chxPXzSsl7ZWRAuOIE23GDNzjWuZquvFlgA8xmpunjU=
-github.com/davecgh/go-spew v1.1.0 h1:ZDRjVQ15GmhC3fiQ8ni8+OwkZQO4DARzQgrnXU1Liz8=
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+github.com/alexbrainman/sspi v0.0.0-20210105120005-909beea2cc74/go.mod h1:cEWa1LVoE5KvSD9ONXsZrj0z6KqySlCCNKHlLzbqAt4=
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