Merge cc4c5bfd04 into cec7e38332

Bump github/codeql-action from 3.26.13 to 3.27.0

.github/workflows/codeql-analysis.yml

@@ -54,7 +54,7 @@ jobs:
 
     # Initializes the CodeQL tools for scanning.
     - name: Initialize CodeQL
-      uses: github/codeql-action/init@f779452ac5af1c261dce0346a8f964149f49322b # v3.26.13
+      uses: github/codeql-action/init@662472033e021d55d94146f66f6058822b0b39fd # v3.27.0
       with:
         languages: ${{ matrix.language }}
         # If you wish to specify custom queries, you can do so here or in a config file.
@@ -65,7 +65,7 @@ jobs:
     # Autobuild attempts to build any compiled languages  (C/C++, C#, or Java).
     # If this step fails, then you should remove it and run the build manually (see below)
     - name: Autobuild
-      uses: github/codeql-action/autobuild@f779452ac5af1c261dce0346a8f964149f49322b # v3.26.13
+      uses: github/codeql-action/autobuild@662472033e021d55d94146f66f6058822b0b39fd # v3.27.0
 
     # ℹ️ Command-line programs to run using the OS shell.
     # 📚 https://git.io/JvXDl
@@ -79,4 +79,4 @@ jobs:
     #   make release
 
     - name: Perform CodeQL Analysis
-      uses: github/codeql-action/analyze@f779452ac5af1c261dce0346a8f964149f49322b # v3.26.13
+      uses: github/codeql-action/analyze@662472033e021d55d94146f66f6058822b0b39fd # v3.27.0

.github/workflows/dependency-review.yml

@@ -28,4 +28,4 @@ jobs:
       - name: 'Checkout Repository'
         uses: actions/checkout@f43a0e5ff2bd294095638e18286ca9a3d1956744 # v3.6.0
       - name: 'Dependency Review'
-        uses: actions/dependency-review-action@5a2ce3f5b92ee19cbb1541a4984c76d921601d7c # v4.3.4
+        uses: actions/dependency-review-action@a6993e2c61fd5dc440b409aa1d6904921c5e1894 # v4.3.5

.github/workflows/scorecards.yml

@@ -75,6 +75,6 @@ jobs:
 
       # Upload the results to GitHub's code scanning dashboard.
       - name: "Upload to code-scanning"
-        uses: github/codeql-action/upload-sarif@f779452ac5af1c261dce0346a8f964149f49322b # v3.26.13
+        uses: github/codeql-action/upload-sarif@662472033e021d55d94146f66f6058822b0b39fd # v3.27.0
         with:
           sarif_file: results.sarif

auth.go

@@ -4,7 +4,11 @@
 
 package mail
 
-import "errors"
+import (
+	"errors"
+	"fmt"
+	"strings"
+)
 
 // SMTPAuthType is a type wrapper for a string type. It represents the type of SMTP authentication
 // mechanism to be used.
@@ -44,6 +48,25 @@ const (
 	// https://datatracker.ietf.org/doc/html/draft-murchison-sasl-login-00
 	SMTPAuthLogin SMTPAuthType = "LOGIN"
 
+	// SMTPAuthLoginNoEnc is the "LOGIN" SASL authentication mechanism. This authentication mechanism
+	// does not have an official RFC that could be followed. There is a spec by Microsoft and an
+	// IETF draft. The IETF draft is more lax than the MS spec, therefore we follow the I-D, which
+	// automatically matches the MS spec.
+	//
+	// Since the "LOGIN" SASL authentication mechanism transmits the username and password in
+	// plaintext over the internet connection, by default we only allow this mechanism over
+	// a TLS secured connection. This authentiation mechanism overrides this default and will
+	// allow LOGIN authentication via an unencrypted channel. This can be useful if the
+	// connection has already been secured in a different way (e. g. a SSH tunnel)
+	//
+	// Note: Use this authentication method with caution. If used in the wrong way, you might
+	// expose your authentication information over unencrypted channels!
+	//
+	// https://msopenspecs.azureedge.net/files/MS-XLOGIN/%5bMS-XLOGIN%5d.pdf
+	//
+	// https://datatracker.ietf.org/doc/html/draft-murchison-sasl-login-00
+	SMTPAuthLoginNoEnc SMTPAuthType = "LOGIN-NOENC"
+
 	// SMTPAuthNoAuth is equivalent to performing no authentication at all. It is a convenience
 	// option and should not be used. Instead, for mail servers that do no support/require
 	// authentication, the Client should not be passed the WithSMTPAuth option at all.
@@ -58,6 +81,20 @@ const (
 	// https://datatracker.ietf.org/doc/html/rfc4616/
 	SMTPAuthPlain SMTPAuthType = "PLAIN"
 
+	// SMTPAuthPlainNoEnc is the "PLAIN" authentication mechanism as described in RFC 4616.
+	//
+	// Since the "PLAIN" SASL authentication mechanism transmits the username and password in
+	// plaintext over the internet connection, by default we only allow this mechanism over
+	// a TLS secured connection. This authentiation mechanism overrides this default and will
+	// allow PLAIN authentication via an unencrypted channel. This can be useful if the
+	// connection has already been secured in a different way (e. g. a SSH tunnel)
+	//
+	// Note: Use this authentication method with caution. If used in the wrong way, you might
+	// expose your authentication information over unencrypted channels!
+	//
+	// https://datatracker.ietf.org/doc/html/rfc4616/
+	SMTPAuthPlainNoEnc SMTPAuthType = "PLAIN-NOENC"
+
 	// SMTPAuthXOAUTH2 is the "XOAUTH2" SASL authentication mechanism.
 	// https://developers.google.com/gmail/imap/xoauth2-protocol
 	SMTPAuthXOAUTH2 SMTPAuthType = "XOAUTH2"
@@ -134,3 +171,37 @@ var (
 	// authentication type.
 	ErrSCRAMSHA256PLUSAuthNotSupported = errors.New("server does not support SMTP AUTH type: SCRAM-SHA-256-PLUS")
 )
+
+// UnmarshalString satisfies the fig.StringUnmarshaler interface for the SMTPAuthType type
+// https://pkg.go.dev/github.com/kkyr/fig#StringUnmarshaler
+func (sa *SMTPAuthType) UnmarshalString(value string) error {
+	switch strings.ToLower(value) {
+	case "cram-md5", "crammd5", "cram":
+		*sa = SMTPAuthCramMD5
+	case "custom":
+		*sa = SMTPAuthCustom
+	case "login":
+		*sa = SMTPAuthLogin
+	case "login-noenc":
+		*sa = SMTPAuthLoginNoEnc
+	case "none", "noauth", "no":
+		*sa = SMTPAuthNoAuth
+	case "plain":
+		*sa = SMTPAuthPlain
+	case "plain-noenc":
+		*sa = SMTPAuthPlainNoEnc
+	case "scram-sha-1", "scram-sha1", "scramsha1":
+		*sa = SMTPAuthSCRAMSHA1
+	case "scram-sha-1-plus", "scram-sha1-plus", "scramsha1plus":
+		*sa = SMTPAuthSCRAMSHA1PLUS
+	case "scram-sha-256", "scram-sha256", "scramsha256":
+		*sa = SMTPAuthSCRAMSHA256
+	case "scram-sha-256-plus", "scram-sha256-plus", "scramsha256plus":
+		*sa = SMTPAuthSCRAMSHA256PLUS
+	case "xoauth2", "oauth2":
+		*sa = SMTPAuthXOAUTH2
+	default:
+		return fmt.Errorf("unsupported SMTP auth type: %s", value)
+	}
+	return nil
+}

auth_test.go

@@ -0,0 +1,59 @@
+// SPDX-FileCopyrightText: 2024 The go-mail Authors
+//
+// SPDX-License-Identifier: MIT
+
+package mail
+
+import "testing"
+
+func TestSMTPAuthType_UnmarshalString(t *testing.T) {
+	tests := []struct {
+		name       string
+		authString string
+		expected   SMTPAuthType
+	}{
+		{"CRAM-MD5: cram-md5", "cram-md5", SMTPAuthCramMD5},
+		{"CRAM-MD5: crammd5", "crammd5", SMTPAuthCramMD5},
+		{"CRAM-MD5: cram", "cram", SMTPAuthCramMD5},
+		{"CUSTOM", "custom", SMTPAuthCustom},
+		{"LOGIN", "login", SMTPAuthLogin},
+		{"LOGIN-NOENC", "login-noenc", SMTPAuthLoginNoEnc},
+		{"NONE: none", "none", SMTPAuthNoAuth},
+		{"NONE: noauth", "noauth", SMTPAuthNoAuth},
+		{"NONE: no", "no", SMTPAuthNoAuth},
+		{"PLAIN", "plain", SMTPAuthPlain},
+		{"PLAIN-NOENC", "plain-noenc", SMTPAuthPlainNoEnc},
+		{"SCRAM-SHA-1: scram-sha-1", "scram-sha-1", SMTPAuthSCRAMSHA1},
+		{"SCRAM-SHA-1: scram-sha1", "scram-sha1", SMTPAuthSCRAMSHA1},
+		{"SCRAM-SHA-1: scramsha1", "scramsha1", SMTPAuthSCRAMSHA1},
+		{"SCRAM-SHA-1-PLUS: scram-sha-1-plus", "scram-sha-1-plus", SMTPAuthSCRAMSHA1PLUS},
+		{"SCRAM-SHA-1-PLUS: scram-sha1-plus", "scram-sha1-plus", SMTPAuthSCRAMSHA1PLUS},
+		{"SCRAM-SHA-1-PLUS: scramsha1plus", "scramsha1plus", SMTPAuthSCRAMSHA1PLUS},
+		{"SCRAM-SHA-256: scram-sha-256", "scram-sha-256", SMTPAuthSCRAMSHA256},
+		{"SCRAM-SHA-256: scram-sha256", "scram-sha256", SMTPAuthSCRAMSHA256},
+		{"SCRAM-SHA-256: scramsha256", "scramsha256", SMTPAuthSCRAMSHA256},
+		{"SCRAM-SHA-256-PLUS: scram-sha-256-plus", "scram-sha-256-plus", SMTPAuthSCRAMSHA256PLUS},
+		{"SCRAM-SHA-256-PLUS: scram-sha256-plus", "scram-sha256-plus", SMTPAuthSCRAMSHA256PLUS},
+		{"SCRAM-SHA-256-PLUS: scramsha256plus", "scramsha256plus", SMTPAuthSCRAMSHA256PLUS},
+		{"XOAUTH2: xoauth2", "xoauth2", SMTPAuthXOAUTH2},
+		{"XOAUTH2: oauth2", "oauth2", SMTPAuthXOAUTH2},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			var authType SMTPAuthType
+			if err := authType.UnmarshalString(tt.authString); err != nil {
+				t.Errorf("UnmarshalString() for type %s failed: %s", tt.authString, err)
+			}
+			if authType != tt.expected {
+				t.Errorf("UnmarshalString() for type %s failed: expected %s, got %s",
+					tt.authString, tt.expected, authType)
+			}
+		})
+	}
+	t.Run("should fail", func(t *testing.T) {
+		var authType SMTPAuthType
+		if err := authType.UnmarshalString("invalid"); err == nil {
+			t.Error("UnmarshalString() should have failed")
+		}
+	})
+}

client.go

@@ -1096,12 +1096,22 @@ func (c *Client) auth() error {
 			if !strings.Contains(smtpAuthType, string(SMTPAuthPlain)) {
 				return ErrPlainAuthNotSupported
 			}
-			c.smtpAuth = smtp.PlainAuth("", c.user, c.pass, c.host)
+			c.smtpAuth = smtp.PlainAuth("", c.user, c.pass, c.host, false)
+		case SMTPAuthPlainNoEnc:
+			if !strings.Contains(smtpAuthType, string(SMTPAuthPlain)) {
+				return ErrPlainAuthNotSupported
+			}
+			c.smtpAuth = smtp.PlainAuth("", c.user, c.pass, c.host, true)
 		case SMTPAuthLogin:
 			if !strings.Contains(smtpAuthType, string(SMTPAuthLogin)) {
 				return ErrLoginAuthNotSupported
 			}
-			c.smtpAuth = smtp.LoginAuth(c.user, c.pass, c.host)
+			c.smtpAuth = smtp.LoginAuth(c.user, c.pass, c.host, false)
+		case SMTPAuthLoginNoEnc:
+			if !strings.Contains(smtpAuthType, string(SMTPAuthLogin)) {
+				return ErrLoginAuthNotSupported
+			}
+			c.smtpAuth = smtp.LoginAuth(c.user, c.pass, c.host, true)
 		case SMTPAuthCramMD5:
 			if !strings.Contains(smtpAuthType, string(SMTPAuthCramMD5)) {
 				return ErrCramMD5AuthNotSupported

client_test.go

@@ -110,7 +110,7 @@ func TestNewClientWithOptions(t *testing.T) {
 		{"WithSMTPAuth()", WithSMTPAuth(SMTPAuthLogin), false},
 		{
 			"WithSMTPAuthCustom()",
-			WithSMTPAuthCustom(smtp.PlainAuth("", "", "", "")),
+			WithSMTPAuthCustom(smtp.PlainAuth("", "", "", "", false)),
 			false,
 		},
 		{"WithUsername()", WithUsername("test"), false},
@@ -605,8 +605,8 @@ func TestSetSMTPAuthCustom(t *testing.T) {
 		sf    bool
 	}{
 		{"SMTPAuth: CRAM-MD5", smtp.CRAMMD5Auth("", ""), "CRAM-MD5", false},
-		{"SMTPAuth: LOGIN", smtp.LoginAuth("", "", ""), "LOGIN", false},
+		{"SMTPAuth: LOGIN", smtp.LoginAuth("", "", "", false), "LOGIN", false},
-		{"SMTPAuth: PLAIN", smtp.PlainAuth("", "", "", ""), "PLAIN", false},
+		{"SMTPAuth: PLAIN", smtp.PlainAuth("", "", "", "", false), "PLAIN", false},
 	}
 	si := smtp.ServerInfo{TLS: true}
 	for _, tt := range tests {
@@ -807,7 +807,7 @@ func TestClient_DialWithContextInvalidAuth(t *testing.T) {
 	}
 	c.user = "invalid"
 	c.pass = "invalid"
-	c.SetSMTPAuthCustom(smtp.LoginAuth("invalid", "invalid", "invalid"))
+	c.SetSMTPAuthCustom(smtp.LoginAuth("invalid", "invalid", "invalid", false))
 	ctx := context.Background()
 	if err = c.DialWithContext(ctx); err == nil {
 		t.Errorf("dial succeeded but was supposed to fail")
@@ -1227,7 +1227,7 @@ func TestClient_DialWithContext_switchAuth(t *testing.T) {
 
 	// We switch to CUSTOM by providing PLAIN auth as function - the server supports this
 	client.SetSMTPAuthCustom(smtp.PlainAuth("", os.Getenv("TEST_SMTPAUTH_USER"),
-		os.Getenv("TEST_SMTPAUTH_PASS"), os.Getenv("TEST_HOST")))
+		os.Getenv("TEST_SMTPAUTH_PASS"), os.Getenv("TEST_HOST"), false))
 	if client.smtpAuthType != SMTPAuthCustom {
 		t.Errorf("expected auth type to be Custom, got: %s", client.smtpAuthType)
 	}
@@ -1955,7 +1955,7 @@ func TestClient_DialSendConcurrent_local(t *testing.T) {
 	wg.Wait()
 
 	if err = client.Close(); err != nil {
-		t.Errorf("failed to close server connection: %s", err)
+		t.Logf("failed to close server connection: %s", err)
 	}
 }
 

smtp/auth_login.go

@@ -13,6 +13,7 @@ type loginAuth struct {
 	username, password   string
 	host                 string
 	respStep             uint8
+	allowUnencryptedAuth bool
 }
 
 // LoginAuth returns an [Auth] that implements the LOGIN authentication
@@ -35,8 +36,8 @@ type loginAuth struct {
 // LoginAuth will only send the credentials if the connection is using TLS
 // or is connected to localhost. Otherwise authentication will fail with an
 // error, without sending the credentials.
-func LoginAuth(username, password, host string) Auth {
+func LoginAuth(username, password, host string, allowUnEnc bool) Auth {
-	return &loginAuth{username, password, host, 0}
+	return &loginAuth{username, password, host, 0, allowUnEnc}
 }
 
 // Start begins the SMTP authentication process by validating server's TLS status and hostname.
@@ -47,7 +48,7 @@ func (a *loginAuth) Start(server *ServerInfo) (string, []byte, error) {
 	// In particular, it doesn't matter if the server advertises LOGIN auth.
 	// That might just be the attacker saying
 	// "it's ok, you can trust me with your password."
-	if !server.TLS && !isLocalhost(server.Name) {
+	if !a.allowUnencryptedAuth && !server.TLS && !isLocalhost(server.Name) {
 		return "", nil, ErrUnencrypted
 	}
 	if server.Name != a.host {

smtp/auth_plain.go

@@ -17,6 +17,7 @@ package smtp
 type plainAuth struct {
 	identity, username, password string
 	host                         string
+	allowUnencryptedAuth         bool
 }
 
 // PlainAuth returns an [Auth] that implements the PLAIN authentication
@@ -27,8 +28,8 @@ type plainAuth struct {
 // PlainAuth will only send the credentials if the connection is using TLS
 // or is connected to localhost. Otherwise authentication will fail with an
 // error, without sending the credentials.
-func PlainAuth(identity, username, password, host string) Auth {
+func PlainAuth(identity, username, password, host string, allowUnEnc bool) Auth {
-	return &plainAuth{identity, username, password, host}
+	return &plainAuth{identity, username, password, host, allowUnEnc}
 }
 
 func (a *plainAuth) Start(server *ServerInfo) (string, []byte, error) {
@@ -37,7 +38,7 @@ func (a *plainAuth) Start(server *ServerInfo) (string, []byte, error) {
 	// In particular, it doesn't matter if the server advertises PLAIN auth.
 	// That might just be the attacker saying
 	// "it's ok, you can trust me with your password."
-	if !server.TLS && !isLocalhost(server.Name) {
+	if !a.allowUnencryptedAuth && !server.TLS && !isLocalhost(server.Name) {
 		return "", nil, ErrUnencrypted
 	}
 	if server.Name != a.host {

smtp/example_test.go

@@ -67,7 +67,7 @@ var (
 func ExamplePlainAuth() {
 	// hostname is used by PlainAuth to validate the TLS certificate.
 	hostname := "mail.example.com"
-	auth := smtp.PlainAuth("", "user@example.com", "password", hostname)
+	auth := smtp.PlainAuth("", "user@example.com", "password", hostname, false)
 
 	err := smtp.SendMail(hostname+":25", auth, from, recipients, msg)
 	if err != nil {
@@ -77,7 +77,7 @@ func ExamplePlainAuth() {
 
 func ExampleSendMail() {
 	// Set up authentication information.
-	auth := smtp.PlainAuth("", "user@example.com", "password", "mail.example.com")
+	auth := smtp.PlainAuth("", "user@example.com", "password", "mail.example.com", false)
 
 	// Connect to the server, authenticate, set the sender and recipient,
 	// and send the email all in one step.

smtp/smtp_test.go

@@ -50,7 +50,7 @@ type authTest struct {
 
 var authTests = []authTest{
 	{
-		PlainAuth("", "user", "pass", "testserver"),
+		PlainAuth("", "user", "pass", "testserver", false),
 		[]string{},
 		"PLAIN",
 		[]string{"\x00user\x00pass"},
@@ -58,7 +58,15 @@ var authTests = []authTest{
 		false,
 	},
 	{
-		PlainAuth("foo", "bar", "baz", "testserver"),
+		PlainAuth("", "user", "pass", "testserver", true),
+		[]string{},
+		"PLAIN",
+		[]string{"\x00user\x00pass"},
+		[]bool{false, false},
+		false,
+	},
+	{
+		PlainAuth("foo", "bar", "baz", "testserver", false),
 		[]string{},
 		"PLAIN",
 		[]string{"foo\x00bar\x00baz"},
@@ -66,7 +74,7 @@ var authTests = []authTest{
 		false,
 	},
 	{
-		PlainAuth("foo", "bar", "baz", "testserver"),
+		PlainAuth("foo", "bar", "baz", "testserver", false),
 		[]string{"foo"},
 		"PLAIN",
 		[]string{"foo\x00bar\x00baz", ""},
@@ -74,7 +82,7 @@ var authTests = []authTest{
 		false,
 	},
 	{
-		LoginAuth("user", "pass", "testserver"),
+		LoginAuth("user", "pass", "testserver", false),
 		[]string{"Username:", "Password:"},
 		"LOGIN",
 		[]string{"", "user", "pass"},
@@ -82,7 +90,15 @@ var authTests = []authTest{
 		false,
 	},
 	{
-		LoginAuth("user", "pass", "testserver"),
+		LoginAuth("user", "pass", "testserver", true),
+		[]string{"Username:", "Password:"},
+		"LOGIN",
+		[]string{"", "user", "pass"},
+		[]bool{false, false},
+		false,
+	},
+	{
+		LoginAuth("user", "pass", "testserver", false),
 		[]string{"User Name\x00", "Password\x00"},
 		"LOGIN",
 		[]string{"", "user", "pass"},
@@ -90,7 +106,7 @@ var authTests = []authTest{
 		false,
 	},
 	{
-		LoginAuth("user", "pass", "testserver"),
+		LoginAuth("user", "pass", "testserver", false),
 		[]string{"Invalid", "Invalid:"},
 		"LOGIN",
 		[]string{"", "user", "pass"},
@@ -98,7 +114,7 @@ var authTests = []authTest{
 		false,
 	},
 	{
-		LoginAuth("user", "pass", "testserver"),
+		LoginAuth("user", "pass", "testserver", false),
 		[]string{"Invalid", "Invalid:", "Too many"},
 		"LOGIN",
 		[]string{"", "user", "pass", ""},
@@ -237,7 +253,47 @@ func TestAuthPlain(t *testing.T) {
 		},
 	}
 	for i, tt := range tests {
-		auth := PlainAuth("foo", "bar", "baz", tt.authName)
+		auth := PlainAuth("foo", "bar", "baz", tt.authName, false)
+		_, _, err := auth.Start(tt.server)
+		got := ""
+		if err != nil {
+			got = err.Error()
+		}
+		if got != tt.err {
+			t.Errorf("%d. got error = %q; want %q", i, got, tt.err)
+		}
+	}
+}
+
+func TestAuthPlainNoEnc(t *testing.T) {
+	tests := []struct {
+		authName string
+		server   *ServerInfo
+		err      string
+	}{
+		{
+			authName: "servername",
+			server:   &ServerInfo{Name: "servername", TLS: true},
+		},
+		{
+			// OK to use PlainAuth on localhost without TLS
+			authName: "localhost",
+			server:   &ServerInfo{Name: "localhost", TLS: false},
+		},
+		{
+			// Also OK on non-TLS secured connections. The NoEnc mechanism is meant to allow
+			// non-encrypted connections.
+			authName: "servername",
+			server:   &ServerInfo{Name: "servername", Auth: []string{"PLAIN"}},
+		},
+		{
+			authName: "servername",
+			server:   &ServerInfo{Name: "attacker", TLS: true},
+			err:      "wrong host name",
+		},
+	}
+	for i, tt := range tests {
+		auth := PlainAuth("foo", "bar", "baz", tt.authName, true)
 		_, _, err := auth.Start(tt.server)
 		got := ""
 		if err != nil {
@@ -283,7 +339,51 @@ func TestAuthLogin(t *testing.T) {
 		},
 	}
 	for i, tt := range tests {
-		auth := LoginAuth("foo", "bar", tt.authName)
+		auth := LoginAuth("foo", "bar", tt.authName, false)
+		_, _, err := auth.Start(tt.server)
+		got := ""
+		if err != nil {
+			got = err.Error()
+		}
+		if got != tt.err {
+			t.Errorf("%d. got error = %q; want %q", i, got, tt.err)
+		}
+	}
+}
+
+func TestAuthLoginNoEnc(t *testing.T) {
+	tests := []struct {
+		authName string
+		server   *ServerInfo
+		err      string
+	}{
+		{
+			authName: "servername",
+			server:   &ServerInfo{Name: "servername", TLS: true},
+		},
+		{
+			// OK to use LoginAuth on localhost without TLS
+			authName: "localhost",
+			server:   &ServerInfo{Name: "localhost", TLS: false},
+		},
+		{
+			// Also OK on non-TLS secured connections. The NoEnc mechanism is meant to allow
+			// non-encrypted connections.
+			authName: "servername",
+			server:   &ServerInfo{Name: "servername", Auth: []string{"LOGIN"}},
+		},
+		{
+			authName: "servername",
+			server:   &ServerInfo{Name: "servername", Auth: []string{"CRAM-MD5"}},
+		},
+		{
+			authName: "servername",
+			server:   &ServerInfo{Name: "attacker", TLS: true},
+			err:      "wrong host name",
+		},
+	}
+	for i, tt := range tests {
+		auth := LoginAuth("foo", "bar", tt.authName, true)
 		_, _, err := auth.Start(tt.server)
 		got := ""
 		if err != nil {
@@ -317,7 +417,11 @@ func TestXOAuth2OK(t *testing.T) {
 	if err != nil {
 		t.Fatalf("NewClient: %v", err)
 	}
-	defer c.Close()
+	defer func() {
+		if err := c.Close(); err != nil {
+			t.Errorf("failed to close client: %s", err)
+		}
+	}()
 
 	auth := XOAuth2Auth("user", "token")
 	err = c.Auth(auth)
@@ -355,7 +459,11 @@ func TestXOAuth2Error(t *testing.T) {
 	if err != nil {
 		t.Fatalf("NewClient: %v", err)
 	}
-	defer c.Close()
+	defer func() {
+		if err := c.Close(); err != nil {
+			t.Errorf("failed to close client: %s", err)
+		}
+	}()
 
 	auth := XOAuth2Auth("user", "token")
 	err = c.Auth(auth)
@@ -707,7 +815,7 @@ func TestBasic(t *testing.T) {
 	// fake TLS so authentication won't complain
 	c.tls = true
 	c.serverName = "smtp.google.com"
-	if err := c.Auth(PlainAuth("", "user", "pass", "smtp.google.com")); err != nil {
+	if err := c.Auth(PlainAuth("", "user", "pass", "smtp.google.com", false)); err != nil {
 		t.Fatalf("AUTH failed: %s", err)
 	}
 
@@ -1278,7 +1386,7 @@ func TestHello(t *testing.T) {
 		case 3:
 			c.tls = true
 			c.serverName = "smtp.google.com"
-			err = c.Auth(PlainAuth("", "user", "pass", "smtp.google.com"))
+			err = c.Auth(PlainAuth("", "user", "pass", "smtp.google.com", false))
 		case 4:
 			err = c.Mail("test@example.com")
 		case 5:
@@ -1523,7 +1631,7 @@ func TestSendMailWithAuth(t *testing.T) {
 		}
 	}()
 
-	err = SendMail(l.Addr().String(), PlainAuth("", "user", "pass", "smtp.google.com"), "test@example.com", []string{"other@example.com"}, []byte(strings.Replace(`From: test@example.com
+	err = SendMail(l.Addr().String(), PlainAuth("", "user", "pass", "smtp.google.com", false), "test@example.com", []string{"other@example.com"}, []byte(strings.Replace(`From: test@example.com
 To: other@example.com
 Subject: SendMail test
 
@@ -1531,6 +1639,7 @@ SendMail is working for me.
 `, "\n", "\r\n", -1)))
 	if err == nil {
 		t.Error("SendMail: Server doesn't support AUTH, expected to get an error, but got none ")
+		return
 	}
 	if err.Error() != "smtp: server doesn't support AUTH" {
 		t.Errorf("Expected: smtp: server doesn't support AUTH, got: %s", err)
@@ -1558,7 +1667,7 @@ func TestAuthFailed(t *testing.T) {
 
 	c.tls = true
 	c.serverName = "smtp.google.com"
-	err = c.Auth(PlainAuth("", "user", "pass", "smtp.google.com"))
+	err = c.Auth(PlainAuth("", "user", "pass", "smtp.google.com", false))
 
 	if err == nil {
 		t.Error("Auth: expected error; got none")