Support LOGIN authentication on outgoing SMTP server

PR:		#1
Obtained from:	https://gist.github.com/andelf/5118732

config.go

@@ -25,6 +25,7 @@ var (
 	remoteHost        = flag.String("remote_host", "smtp.gmail.com:587", "Outgoing SMTP server")
 	remoteUser        = flag.String("remote_user", "", "Username for authentication on outgoing SMTP server")
 	remotePass        = flag.String("remote_pass", "", "Password for authentication on outgoing SMTP server")
+	remoteAuth        = flag.String("remote_auth", "plain", "Auth method on outgoing SMTP server (plain, login)")
 	remoteSender      = flag.String("remote_sender", "", "Sender e-mail address on outgoing SMTP server")
 	versionInfo       = flag.Bool("version", false, "Show version information")
 )

main.go

@@ -110,7 +110,14 @@ func mailHandler(peer smtpd.Peer, env smtpd.Envelope) error {
 	host, _, _ := net.SplitHostPort(*remoteHost)
 
 	if *remoteUser != "" && *remotePass != "" {
-		auth = smtp.PlainAuth("", *remoteUser, *remotePass, host)
+		switch *remoteAuth {
+		case "plain":
+			auth = smtp.PlainAuth("", *remoteUser, *remotePass, host)
+		case "login":
+			auth = LoginAuth(*remoteUser, *remotePass)
+		default:
+			return smtpd.Error{Code: 530, Message: "Authentication method not supported"}
+		}
 	}
 
 	env.AddReceivedLine(peer)

smtp.go

@@ -451,3 +451,30 @@ func validateLine(line string) error {
 	}
 	return nil
 }
+
+// LOGIN authentication
+type loginAuth struct {
+	username, password string
+}
+
+func LoginAuth(username, password string) smtp.Auth {
+	return &loginAuth{username, password}
+}
+
+func (a *loginAuth) Start(server *smtp.ServerInfo) (string, []byte, error) {
+	return "LOGIN", []byte{}, nil
+}
+
+func (a *loginAuth) Next(fromServer []byte, more bool) ([]byte, error) {
+	if more {
+		switch string(fromServer) {
+		case "Username:":
+			return []byte(a.username), nil
+		case "Password:":
+			return []byte(a.password), nil
+		default:
+			return nil, errors.New("Unkown fromServer")
+		}
+	}
+	return nil, nil
+}

smtprelay.ini

@@ -55,5 +55,9 @@
 ;remote_user =
 ;remote_pass =
 
+; Authentication method on outgoing SMTP server
+; (plain, login)
+;remote_auth = plain
+
 ; Sender e-mail address on outgoing SMTP server
 ;remote_sender =