From 9dcd716f91262b3709fcbddf25458fe49a442a0a Mon Sep 17 00:00:00 2001
From: Kailash Nadh <kailash@nadh.in>
Date: Wed, 1 Apr 2020 19:56:40 +0530
Subject: [PATCH] Add support for SMTP 'LOGIN' auth

---
 config.toml.sample            |  2 +-
 internal/messenger/emailer.go | 37 +++++++++++++++++++++++++++++++++--
 2 files changed, 36 insertions(+), 3 deletions(-)

diff --git a/config.toml.sample b/config.toml.sample
index 93545f0..962c4ca 100644
--- a/config.toml.sample
+++ b/config.toml.sample
@@ -79,7 +79,7 @@ max_idle = 10
         host = "my.smtp.server"
         port = "25"
 
-        # cram | plain | empty for no auth
+        # "cram", "plain", or "login". Empty string for no auth.
         auth_protocol = "cram"
         username = "xxxxx"
         password = ""
diff --git a/internal/messenger/emailer.go b/internal/messenger/emailer.go
index 36f1291..7e22fc8 100644
--- a/internal/messenger/emailer.go
+++ b/internal/messenger/emailer.go
@@ -1,6 +1,7 @@
 package messenger
 
 import (
+	"errors"
 	"fmt"
 	"math/rand"
 	"net/smtp"
@@ -11,6 +12,12 @@ import (
 
 const emName = "email"
 
+// loginAuth is used for enabling SMTP "LOGIN" auth.
+type loginAuth struct {
+	username string
+	password string
+}
+
 // Server represents an SMTP server's credentials.
 type Server struct {
 	Name          string
@@ -42,10 +49,16 @@ func NewEmailer(srv ...Server) (Messenger, error) {
 	for _, server := range srv {
 		s := server
 		var auth smtp.Auth
-		if s.AuthProtocol == "cram" {
+		switch s.AuthProtocol {
+		case "cram":
 			auth = smtp.CRAMMD5Auth(s.Username, s.Password)
-		} else if s.AuthProtocol == "plain" {
+		case "plain":
 			auth = smtp.PlainAuth("", s.Username, s.Password, s.Host)
+		case "login":
+			auth = &loginAuth{username: s.Username, password: s.Password}
+		case "":
+		default:
+			return nil, fmt.Errorf("unknown SMTP auth typer '%s'", s.AuthProtocol)
 		}
 
 		pool, err := email.NewPool(fmt.Sprintf("%s:%d", s.Host, s.Port), s.MaxConns, auth)
@@ -115,3 +128,23 @@ func (e *emailer) Push(fromAddr string, toAddr []string, subject string, m []byt
 func (e *emailer) Flush() error {
 	return nil
 }
+
+// https://gist.github.com/andelf/5118732
+// Adds support for SMTP LOGIN auth.
+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 SMTP fromServer")
+		}
+	}
+	return nil, nil
+}