Merge pull request #317 from wneessen/more-auth-test-coverage

More test coverage for smtp/auth

smtp/auth.go

@@ -13,6 +13,19 @@
 
 package smtp
 
+import "errors"
+
+var (
+	// ErrUnencrypted is an error indicating that the connection is not encrypted.
+	ErrUnencrypted = errors.New("unencrypted connection")
+	// ErrUnexpectedServerChallange is an error indicating that the server issued an unexpected challenge.
+	ErrUnexpectedServerChallange = errors.New("unexpected server challenge")
+	// ErrUnexpectedServerResponse is an error indicating that the server issued an unexpected response.
+	ErrUnexpectedServerResponse = errors.New("unexpected server response")
+	// ErrWrongHostname is an error indicating that the provided hostname does not match the expected value.
+	ErrWrongHostname = errors.New("wrong host name")
+)
+
 // Auth is implemented by an SMTP authentication mechanism.
 type Auth interface {
 	// Start begins an authentication with a server.

smtp/auth_login.go

@@ -5,13 +5,9 @@
 package smtp
 
 import (
-	"errors"
 	"fmt"
 )
 
-// ErrUnencrypted is an error indicating that the connection is not encrypted.
-var ErrUnencrypted = errors.New("unencrypted connection")
-
 // loginAuth is the type that satisfies the Auth interface for the "SMTP LOGIN" auth
 type loginAuth struct {
 	username, password string
@@ -55,7 +51,7 @@ func (a *loginAuth) Start(server *ServerInfo) (string, []byte, error) {
 		return "", nil, ErrUnencrypted
 	}
 	if server.Name != a.host {
-		return "", nil, errors.New("wrong host name")
+		return "", nil, ErrWrongHostname
 	}
 	a.respStep = 0
 	return "LOGIN", nil, nil
@@ -73,7 +69,7 @@ func (a *loginAuth) Next(fromServer []byte, more bool) ([]byte, error) {
 			a.respStep++
 			return []byte(a.password), nil
 		default:
-			return nil, fmt.Errorf("unexpected server response: %s", string(fromServer))
+			return nil, fmt.Errorf("%w: %s", ErrUnexpectedServerResponse, string(fromServer))
 		}
 	}
 	return nil, nil

smtp/auth_plain.go

@@ -13,10 +13,6 @@
 
 package smtp
 
-import (
-	"errors"
-)
-
 // plainAuth is the type that satisfies the Auth interface for the "SMTP PLAIN" auth
 type plainAuth struct {
 	identity, username, password string
@@ -42,10 +38,10 @@ func (a *plainAuth) Start(server *ServerInfo) (string, []byte, error) {
 	// That might just be the attacker saying
 	// "it's ok, you can trust me with your password."
 	if !server.TLS && !isLocalhost(server.Name) {
-		return "", nil, errors.New("unencrypted connection")
+		return "", nil, ErrUnencrypted
 	}
 	if server.Name != a.host {
-		return "", nil, errors.New("wrong host name")
+		return "", nil, ErrWrongHostname
 	}
 	resp := []byte(a.identity + "\x00" + a.username + "\x00" + a.password)
 	return "PLAIN", resp, nil
@@ -54,7 +50,7 @@ func (a *plainAuth) Start(server *ServerInfo) (string, []byte, error) {
 func (a *plainAuth) Next(_ []byte, more bool) ([]byte, error) {
 	if more {
 		// We've already sent everything.
-		return nil, errors.New("unexpected server challenge")
+		return nil, ErrUnexpectedServerChallange
 	}
 	return nil, nil
 }

smtp/auth_scram.go

@@ -112,7 +112,7 @@ func (a *scramAuth) Next(fromServer []byte, more bool) ([]byte, error) {
 			return resp, nil
 		default:
 			a.reset()
-			return nil, errors.New("unexpected server response")
+			return nil, fmt.Errorf("%w: %s", ErrUnexpectedServerResponse, string(fromServer))
 		}
 	}
 	return nil, nil
@@ -147,6 +147,9 @@ func (a *scramAuth) initialClientMessage() ([]byte, error) {
 
 	// SCRAM-SHA-X-PLUS auth requires channel binding
 	if a.isPlus {
+		if a.tlsConnState == nil {
+			return nil, errors.New("tls connection state is required for SCRAM-SHA-X-PLUS")
+		}
 		bindType := "tls-unique"
 		connState := a.tlsConnState
 		bindData := connState.TLSUnique

smtp/smtp_test.go

@@ -18,6 +18,7 @@ import (
 	"bytes"
 	"crypto/tls"
 	"crypto/x509"
+	"encoding/base64"
 	"flag"
 	"fmt"
 	"io"
@@ -38,6 +39,7 @@ type authTest struct {
 	name       string
 	responses  []string
 	sf         []bool
+	hasNonce   bool
 }
 
 var authTests = []authTest{
@@ -47,6 +49,7 @@ var authTests = []authTest{
 		"PLAIN",
 		[]string{"\x00user\x00pass"},
 		[]bool{false, false},
+		false,
 	},
 	{
 		PlainAuth("foo", "bar", "baz", "testserver"),
@@ -54,6 +57,15 @@ var authTests = []authTest{
 		"PLAIN",
 		[]string{"foo\x00bar\x00baz"},
 		[]bool{false, false},
+		false,
+	},
+	{
+		PlainAuth("foo", "bar", "baz", "testserver"),
+		[]string{"foo"},
+		"PLAIN",
+		[]string{"foo\x00bar\x00baz", ""},
+		[]bool{true},
+		false,
 	},
 	{
 		LoginAuth("user", "pass", "testserver"),
@@ -61,6 +73,7 @@ var authTests = []authTest{
 		"LOGIN",
 		[]string{"", "user", "pass"},
 		[]bool{false, false},
+		false,
 	},
 	{
 		LoginAuth("user", "pass", "testserver"),
@@ -68,6 +81,7 @@ var authTests = []authTest{
 		"LOGIN",
 		[]string{"", "user", "pass"},
 		[]bool{false, false},
+		false,
 	},
 	{
 		LoginAuth("user", "pass", "testserver"),
@@ -75,6 +89,7 @@ var authTests = []authTest{
 		"LOGIN",
 		[]string{"", "user", "pass"},
 		[]bool{false, false},
+		false,
 	},
 	{
 		LoginAuth("user", "pass", "testserver"),
@@ -82,6 +97,7 @@ var authTests = []authTest{
 		"LOGIN",
 		[]string{"", "user", "pass", ""},
 		[]bool{false, false, true},
+		false,
 	},
 	{
 		CRAMMD5Auth("user", "pass"),
@@ -89,6 +105,7 @@ var authTests = []authTest{
 		"CRAM-MD5",
 		[]string{"", "user 287eb355114cf5c471c26a875f1ca4ae"},
 		[]bool{false, false},
+		false,
 	},
 	{
 		XOAuth2Auth("username", "token"),
@@ -96,6 +113,47 @@ var authTests = []authTest{
 		"XOAUTH2",
 		[]string{"user=username\x01auth=Bearer token\x01\x01", ""},
 		[]bool{false},
+		false,
+	},
+	{
+		ScramSHA1Auth("username", "password"),
+		[]string{"", "r=foo"},
+		"SCRAM-SHA-1",
+		[]string{"", "n,,n=username,r=", ""},
+		[]bool{false, true},
+		true,
+	},
+	{
+		ScramSHA1Auth("username", "password"),
+		[]string{"", "v=foo"},
+		"SCRAM-SHA-1",
+		[]string{"", "n,,n=username,r=", ""},
+		[]bool{false, true},
+		true,
+	},
+	{
+		ScramSHA256Auth("username", "password"),
+		[]string{""},
+		"SCRAM-SHA-256",
+		[]string{"", "n,,n=username,r=", ""},
+		[]bool{false},
+		true,
+	},
+	{
+		ScramSHA1PlusAuth("username", "password", nil),
+		[]string{""},
+		"SCRAM-SHA-1-PLUS",
+		[]string{"", "", ""},
+		[]bool{true},
+		true,
+	},
+	{
+		ScramSHA256PlusAuth("username", "password", nil),
+		[]string{""},
+		"SCRAM-SHA-256-PLUS",
+		[]string{"", "", ""},
+		[]bool{true},
+		true,
 	},
 }
 
@@ -121,10 +179,20 @@ testLoop:
 				t.Errorf("#%d error: %s", i, err)
 				continue testLoop
 			}
+			if test.hasNonce {
+				if !bytes.HasPrefix(resp, expected) {
+					t.Errorf("#%d got response: %s, expected response to start with: %s", i, resp, expected)
+				}
+				continue testLoop
+			}
 			if !bytes.Equal(resp, expected) {
 				t.Errorf("#%d got %s, expected %s", i, resp, expected)
 				continue testLoop
 			}
+			_, err = test.auth.Next([]byte("2.7.0 Authentication successful"), false)
+			if err != nil {
+				t.Errorf("#%d success message error: %s", i, err)
+			}
 		}
 	}
 }
@@ -301,6 +369,106 @@ func TestXOAuth2Error(t *testing.T) {
 	}
 }
 
+func TestAuthSCRAMSHA1_OK(t *testing.T) {
+	hostname := "127.0.0.1"
+	port := "2585"
+
+	go func() {
+		startSMTPServer(false, hostname, port)
+	}()
+	time.Sleep(time.Millisecond * 500)
+
+	conn, err := net.Dial("tcp", fmt.Sprintf("%s:%s", hostname, port))
+	if err != nil {
+		t.Errorf("failed to dial server: %v", err)
+	}
+	client, err := NewClient(conn, hostname)
+	if err != nil {
+		t.Errorf("failed to create client: %v", err)
+	}
+	if err = client.Hello(hostname); err != nil {
+		t.Errorf("failed to send HELO: %v", err)
+	}
+	if err = client.Auth(ScramSHA1Auth("username", "password")); err != nil {
+		t.Errorf("failed to authenticate: %v", err)
+	}
+}
+
+func TestAuthSCRAMSHA256_OK(t *testing.T) {
+	hostname := "127.0.0.1"
+	port := "2586"
+
+	go func() {
+		startSMTPServer(false, hostname, port)
+	}()
+	time.Sleep(time.Millisecond * 500)
+
+	conn, err := net.Dial("tcp", fmt.Sprintf("%s:%s", hostname, port))
+	if err != nil {
+		t.Errorf("failed to dial server: %v", err)
+	}
+	client, err := NewClient(conn, hostname)
+	if err != nil {
+		t.Errorf("failed to create client: %v", err)
+	}
+	if err = client.Hello(hostname); err != nil {
+		t.Errorf("failed to send HELO: %v", err)
+	}
+	if err = client.Auth(ScramSHA256Auth("username", "password")); err != nil {
+		t.Errorf("failed to authenticate: %v", err)
+	}
+}
+
+func TestAuthSCRAMSHA1_fail(t *testing.T) {
+	hostname := "127.0.0.1"
+	port := "2587"
+
+	go func() {
+		startSMTPServer(true, hostname, port)
+	}()
+	time.Sleep(time.Millisecond * 500)
+
+	conn, err := net.Dial("tcp", fmt.Sprintf("%s:%s", hostname, port))
+	if err != nil {
+		t.Errorf("failed to dial server: %v", err)
+	}
+	client, err := NewClient(conn, hostname)
+	if err != nil {
+		t.Errorf("failed to create client: %v", err)
+	}
+	if err = client.Hello(hostname); err != nil {
+		t.Errorf("failed to send HELO: %v", err)
+	}
+	if err = client.Auth(ScramSHA1Auth("username", "password")); err == nil {
+		t.Errorf("expected auth error, got nil")
+	}
+}
+
+func TestAuthSCRAMSHA256_fail(t *testing.T) {
+	hostname := "127.0.0.1"
+	port := "2588"
+
+	go func() {
+		startSMTPServer(true, hostname, port)
+	}()
+	time.Sleep(time.Millisecond * 500)
+
+	conn, err := net.Dial("tcp", fmt.Sprintf("%s:%s", hostname, port))
+	if err != nil {
+		t.Errorf("failed to dial server: %v", err)
+	}
+	client, err := NewClient(conn, hostname)
+	if err != nil {
+		t.Errorf("failed to create client: %v", err)
+	}
+	if err = client.Hello(hostname); err != nil {
+		t.Errorf("failed to send HELO: %v", err)
+	}
+	if err = client.Auth(ScramSHA256Auth("username", "password")); err == nil {
+		t.Errorf("expected auth error, got nil")
+	}
+}
+
 // Issue 17794: don't send a trailing space on AUTH command when there's no password.
 func TestClientAuthTrimSpace(t *testing.T) {
 	server := "220 hello world\r\n" +
@@ -1474,3 +1642,197 @@ func SkipFlaky(t testing.TB, issue int) {
 		t.Skipf("skipping known flaky test without the -flaky flag; see golang.org/issue/%d", issue)
 	}
 }
+
+// testSCRAMSMTPServer represents a test server for SCRAM-based SMTP authentication.
+// It does not do any acutal computation of the challanges but verifies that the expected
+// fields are present. We have actual real authentication tests for all SCRAM modes in the
+// go-mail client_test.go
+type testSCRAMSMTPServer struct {
+	authMechanism string
+	nonce         string
+	hostname      string
+	port          string
+	shouldFail    bool
+}
+
+func (s *testSCRAMSMTPServer) handleConnection(conn net.Conn) {
+	defer func() {
+		_ = conn.Close()
+	}()
+
+	reader := bufio.NewReader(conn)
+	writer := bufio.NewWriter(conn)
+	writeLine := func(data string) error {
+		_, err := writer.WriteString(data + "\r\n")
+		if err != nil {
+			return fmt.Errorf("unable to write line: %w", err)
+		}
+		return writer.Flush()
+	}
+	writeOK := func() {
+		_ = writeLine("250 2.0.0 OK")
+	}
+
+	if err := writeLine("220 go-mail test server ready ESMTP"); err != nil {
+		return
+	}
+
+	data, err := reader.ReadString('\n')
+	if err != nil {
+		return
+	}
+	data = strings.TrimSpace(data)
+	if strings.HasPrefix(data, "EHLO") {
+		_ = writeLine(fmt.Sprintf("250-%s", s.hostname))
+		_ = writeLine("250-AUTH SCRAM-SHA-1 SCRAM-SHA-256")
+		writeOK()
+	} else {
+		_ = writeLine("500 Invalid command")
+		return
+	}
+
+	for {
+		data, err = reader.ReadString('\n')
+		if err != nil {
+			fmt.Printf("failed to read data: %v", err)
+		}
+		data = strings.TrimSpace(data)
+		if strings.HasPrefix(data, "AUTH") {
+			parts := strings.Split(data, " ")
+			if len(parts) < 2 {
+				_ = writeLine("500 Syntax error")
+				return
+			}
+
+			authMechanism := parts[1]
+			if authMechanism != "SCRAM-SHA-1" && authMechanism != "SCRAM-SHA-256" {
+				_ = writeLine("504 Unrecognized authentication mechanism")
+				return
+			}
+			s.authMechanism = authMechanism
+			_ = writeLine("334 ")
+			s.handleSCRAMAuth(conn)
+			return
+		} else {
+			_ = writeLine("500 Invalid command")
+		}
+	}
+}
+
+func (s *testSCRAMSMTPServer) handleSCRAMAuth(conn net.Conn) {
+	reader := bufio.NewReader(conn)
+	writer := bufio.NewWriter(conn)
+	writeLine := func(data string) error {
+		_, err := writer.WriteString(data + "\r\n")
+		if err != nil {
+			return fmt.Errorf("unable to write line: %w", err)
+		}
+		return writer.Flush()
+	}
+
+	data, err := reader.ReadString('\n')
+	if err != nil {
+		_ = writeLine("535 Authentication failed")
+		return
+	}
+	data = strings.TrimSpace(data)
+	decodedMessage, err := base64.StdEncoding.DecodeString(data)
+	if err != nil {
+		_ = writeLine("535 Authentication failed")
+		return
+	}
+	splits := strings.Split(string(decodedMessage), ",")
+	if len(splits) != 4 {
+		_ = writeLine("535 Authentication failed - expected 4 parts")
+		return
+	}
+	if splits[0] != "n" {
+		_ = writeLine("535 Authentication failed - expected n to be in the first part")
+		return
+	}
+	if splits[2] != "n=username" {
+		_ = writeLine("535 Authentication failed - expected n=username to be in the third part")
+		return
+	}
+	if !strings.HasPrefix(splits[3], "r=") {
+		_ = writeLine("535 Authentication failed - expected r= to be in the fourth part")
+		return
+	}
+	clientNonce := s.extractNonce(string(decodedMessage))
+	if clientNonce == "" {
+		_ = writeLine("535 Authentication failed")
+		return
+	}
+
+	s.nonce = clientNonce + "server_nonce"
+	serverFirstMessage := fmt.Sprintf("r=%s,s=%s,i=0", s.nonce, "salt")
+	_ = writeLine(fmt.Sprintf("334 %s", base64.StdEncoding.EncodeToString([]byte(serverFirstMessage))))
+
+	data, err = reader.ReadString('\n')
+	if err != nil {
+		_ = writeLine("535 Authentication failed")
+		return
+	}
+	data = strings.TrimSpace(data)
+	decodedFinalMessage, err := base64.StdEncoding.DecodeString(data)
+	if err != nil {
+		_ = writeLine("535 Authentication failed")
+		return
+	}
+	splits = strings.Split(string(decodedFinalMessage), ",")
+	if splits[0] != "c=biws" {
+		_ = writeLine("535 Authentication failed - expected c=biws to be in the first part")
+		return
+	}
+	if !strings.HasPrefix(splits[1], "r=") {
+		_ = writeLine("535 Authentication failed - expected r to be in the second part")
+		return
+	}
+	if !strings.Contains(splits[1], "server_nonce") {
+		_ = writeLine("535 Authentication failed - expected server_nonce to be in the second part")
+		return
+	}
+	if !strings.HasPrefix(splits[2], "p=") {
+		_ = writeLine("535 Authentication failed - expected p to be in the third part")
+		return
+	}
+
+	if s.shouldFail {
+		_ = writeLine("535 Authentication failed")
+		return
+	}
+	_ = writeLine("235 Authentication successful")
+}
+
+func (s *testSCRAMSMTPServer) extractNonce(message string) string {
+	parts := strings.Split(message, ",")
+	for _, part := range parts {
+		if strings.HasPrefix(part, "r=") {
+			return part[2:]
+		}
+	}
+	return ""
+}
+
+func startSMTPServer(shouldFail bool, hostname, port string) {
+	server := &testSCRAMSMTPServer{
+		hostname:   hostname,
+		port:       port,
+		shouldFail: shouldFail,
+	}
+	listener, err := net.Listen("tcp", fmt.Sprintf("%s:%s", hostname, port))
+	if err != nil {
+		fmt.Printf("Failed to start SMTP server: %v", err)
+	}
+	defer func() {
+		_ = listener.Close()
+	}()
+	for {
+		conn, err := listener.Accept()
+		if err != nil {
+			fmt.Printf("Failed to accept connection: %v", err)
+			continue
+		}
+		go server.handleConnection(conn)
+	}
+}