Add Kerberos (GSSAPI) authentication support

conn.go

@@ -155,6 +155,9 @@ type conn struct {
 
 	// If not nil, notifications will be synchronously sent here
 	notificationHandler func(*Notification)
+
+	// GSSAPI context
+	gss Gss
 }
 
 // Handle driver-side settings in parsed connection string.
@@ -1071,7 +1074,10 @@ func isDriverSetting(key string) bool {
 		return true
 	case "binary_parameters":
 		return true
-
+	case "service":
+		return true
+	case "spn":
+		return true
 	default:
 		return false
 	}
@@ -1151,6 +1157,56 @@ func (cn *conn) auth(r *readBuf, o values) {
 		if r.int32() != 0 {
 			errorf("unexpected authentication response: %q", t)
 		}
+	case 7: // GSSAPI, startup
+		cli, err := NewGSS()
+		if err != nil {
+			errorf("kerberos error: %s", err.Error())
+		}
+
+		var token []byte
+
+		if spn, ok := o["spn"]; ok {
+			// Use the supplied SPN if provided..
+			token, err = cli.GetInitTokenFromSpn(spn)
+		} else {
+			// Allow the kerberos service name to be overridden
+			service := "postgres"
+			if val, ok := o["service"]; ok {
+				service = val
+			}
+
+			token, err = cli.GetInitToken(o["host"], service)
+		}
+
+		if err != nil {
+			errorf("failed to get Kerberos ticket: %q", err)
+		}
+
+		w := cn.writeBuf('p')
+		w.bytes(token)
+		cn.send(w)
+
+		// Store for GSSAPI continue message
+		cn.gss = cli
+
+	case 8: // GSSAPI continue
+
+		if cn.gss == nil {
+			errorf("GSSAPI protocol error")
+		}
+
+		b := []byte(*r)
+
+		done, tokOut, err := cn.gss.Continue(b)
+		if err == nil && !done {
+			w := cn.writeBuf('p')
+			w.bytes(tokOut)
+			cn.send(w)
+		}
+
+		// Errors fall through and read the more detailed message
+		// from the server..
+
 	case 10:
 		sc := scram.NewClient(sha256.New, o["user"], o["password"])
 		sc.Step(nil)

go.mod

@@ -1 +1,14 @@
 module github.com/lib/pq
+
+go 1.13
+
+require (
+	github.com/alexbrainman/sspi v0.0.0-20180613141037-e580b900e9f5 // indirect
+	github.com/jcmturner/gokrb5/v8 v8.2.0
+	golang.org/x/crypto v0.0.0-20200311171314-f7b00557c8c4 // indirect
+	gopkg.in/jcmturner/aescts.v1 v1.0.1 // indirect
+	gopkg.in/jcmturner/dnsutils.v1 v1.0.1 // indirect
+	gopkg.in/jcmturner/goidentity.v3 v3.0.0 // indirect
+	gopkg.in/jcmturner/gokrb5.v7 v7.5.0
+	gopkg.in/jcmturner/rpc.v1 v1.1.0 // indirect
+)

krb.go

@@ -0,0 +1,40 @@
+package pq
+
+import (
+	"net"
+	"strings"
+)
+
+/*
+ *  Basic GSSAPI interface to abstract Windows (SSPI) from Unix
+ *  APIs within the driver
+ */
+
+type Gss interface {
+	GetInitToken(host string, service string) ([]byte, error)
+	GetInitTokenFromSpn(spn string) ([]byte, error)
+	Continue(inToken []byte) (done bool, outToken []byte, err error)
+}
+
+/*
+ *  Find the A record associated with a hostname
+ *  In general, hostnames supplied to the driver should be
+ *  canonicalized because the KDC usually only has one
+ *  principal and not one per potential alias of a host.
+ */
+func canonicalizeHostname(host string) (string, error) {
+	canon := host
+
+	name, err := net.LookupCNAME(host)
+	if err != nil {
+		return "", err
+	}
+
+	name = strings.TrimSuffix(name, ".")
+
+	if name != "" {
+		canon = name
+	}
+
+	return canon, nil
+}

krb_unix.go

@@ -0,0 +1,123 @@
+// +build !windows
+
+package pq
+
+import (
+	"fmt"
+	"os"
+	"os/user"
+	"strings"
+
+	"github.com/jcmturner/gokrb5/v8/client"
+	"github.com/jcmturner/gokrb5/v8/config"
+	"github.com/jcmturner/gokrb5/v8/credentials"
+	"github.com/jcmturner/gokrb5/v8/spnego"
+)
+
+/*
+ * UNIX Kerberos support, using jcmturner's pure-go
+ * implementation
+ */
+
+// Implements the Gss interface
+type gss struct {
+	cli *client.Client
+}
+
+func NewGSS() (Gss, error) {
+	g := &gss{}
+	err := g.init()
+
+	if err != nil {
+		return nil, err
+	}
+
+	return g, nil
+}
+
+func (g *gss) init() error {
+	cfgPath, ok := os.LookupEnv("KRB5_CONFIG")
+	if !ok {
+		cfgPath = "/etc/krb5.conf"
+	}
+
+	cfg, err := config.Load(cfgPath)
+	if err != nil {
+		return err
+	}
+
+	u, err := user.Current()
+	if err != nil {
+		return err
+	}
+
+	ccpath := "/tmp/krb5cc_" + u.Uid
+
+	ccname := os.Getenv("KRB5CCNAME")
+	if strings.HasPrefix(ccname, "FILE:") {
+		ccpath = strings.SplitN(ccname, ":", 2)[1]
+	}
+
+	ccache, err := credentials.LoadCCache(ccpath)
+	if err != nil {
+		return err
+	}
+
+	cl, err := client.NewFromCCache(ccache, cfg, client.DisablePAFXFAST(true))
+	if err != nil {
+		return err
+	}
+
+	cl.Login()
+
+	g.cli = cl
+
+	return nil
+}
+
+func (g *gss) GetInitToken(host string, service string) ([]byte, error) {
+
+	// Resolve the hostname down to an 'A' record, if required (usually, it is)
+	if g.cli.Config.LibDefaults.DNSCanonicalizeHostname {
+		var err error
+		host, err = canonicalizeHostname(host)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	spn := service + "/" + host
+
+	return g.GetInitTokenFromSpn(spn)
+}
+
+func (g *gss) GetInitTokenFromSpn(spn string) ([]byte, error) {
+	s := spnego.SPNEGOClient(g.cli, spn)
+
+	st, err := s.InitSecContext()
+	if err != nil {
+		return nil, fmt.Errorf("kerberos error (InitSecContext): %s", err.Error())
+	}
+
+	b, err := st.Marshal()
+	if err != nil {
+		return nil, fmt.Errorf("kerberos error (Marshaling token): %s", err.Error())
+	}
+
+	return b, nil
+}
+
+func (g *gss) Continue(inToken []byte) (done bool, outToken []byte, err error) {
+	t := &spnego.SPNEGOToken{}
+	err = t.Unmarshal(inToken)
+	if err != nil {
+		return true, nil, fmt.Errorf("kerberos error (Unmarshaling token): %s", err.Error())
+	}
+
+	state := t.NegTokenResp.State()
+	if state != spnego.NegStateAcceptCompleted {
+		return true, nil, fmt.Errorf("kerberos: expected state 'Completed' - got %d", state)
+	}
+
+	return true, nil, nil
+}

krb_windows.go

@@ -0,0 +1,61 @@
+// +build windows
+
+package pq
+
+import (
+	"github.com/alexbrainman/sspi"
+	"github.com/alexbrainman/sspi/negotiate"
+)
+
+type gss struct {
+	creds *sspi.Credentials
+	ctx   *negotiate.ClientContext
+}
+
+func NewGSS() (Gss, error) {
+	g := &gss{}
+	err := g.init()
+
+	if err != nil {
+		return nil, err
+	}
+
+	return g, nil
+}
+
+func (g *gss) init() error {
+	creds, err := negotiate.AcquireCurrentUserCredentials()
+	if err != nil {
+		return err
+	}
+
+	g.creds = creds
+	return nil
+}
+
+func (g *gss) GetInitToken(host string, service string) ([]byte, error) {
+
+	host, err := canonicalizeHostname(host)
+	if err != nil {
+		return nil, err
+	}
+
+	spn := service + "/" + host
+
+	return g.GetInitTokenFromSpn(spn)
+}
+
+func (g *gss) GetInitTokenFromSpn(spn string) ([]byte, error) {
+	ctx, token, err := negotiate.NewClientContext(g.creds, spn)
+	if err != nil {
+		return nil, err
+	}
+
+	g.ctx = ctx
+
+	return token, nil
+}
+
+func (g *gss) Continue(inToken []byte) (done bool, outToken []byte, err error) {
+	return g.ctx.Update(inToken)
+}