golang net/smtp SMTP AUTH LOGIN Auth Handler

smtp_login_auth.go

// MIT license (c) andelf 2013


import (
	"net/smtp"
	"errors"
)

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
}


// usage: 
// auth := LoginAuth("loginname", "password")
// err := smtp.SendMail(smtpServer + ":25", auth, fromAddress, toAddresses, []byte(message))
// or	
// client, err := smtp.Dial(smtpServer)
// client.Auth(LoginAuth("loginname", "password"))

This worked for me using:
Server: smtp-mail.outlook.com
Port: 587
SMTP security: STARTTLS

Thank you for posting.

thx dude!

this works! many thanks!

Oh, it's so beautiful.

666

Very useful, Thanks for your code, this works for me!

Also, there is login auth support in go-mail package https://github.com/go-gomail/gomail/blob/master/auth.go

Thank you so much!
Solution still working fine.

And if you don't want to choose between PLAIN and LOGIN:

func PlainOrLoginAuth(username, password, host string) smtp.Auth {
	return &plainOrLoginAuth{username: username, password: password, host: host}
}

func isLocalhost(name string) bool {
	return name == "localhost" || name == "127.0.0.1" || name == "::1"
}

type plainOrLoginAuth struct {
	username   string
	password   string
	host       string
	authMethod string
}

func (a *plainOrLoginAuth) Start(server *smtp.ServerInfo) (string, []byte, error) {
	// Must have TLS, or else localhost server.
	// Note: If TLS is not true, then we can't trust ANYTHING in ServerInfo.
	// 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) {
		return "", nil, errors.New("unencrypted connection")
	}
	if server.Name != a.host {
		return "", nil, errors.New("wrong host name")
	}
	if !slices.Contains(server.Auth, "PLAIN") {
		a.authMethod = "LOGIN"
		return a.authMethod, nil, nil
	} else {
		a.authMethod = "PLAIN"
		resp := []byte("\x00" + a.username + "\x00" + a.password)
		return a.authMethod, resp, nil
	}
}

func (a *plainOrLoginAuth) Next(fromServer []byte, more bool) ([]byte, error) {
	if !more {
		return nil, nil
	}

	if a.authMethod == "PLAIN" {
		// We've already sent everything.
		return nil, errors.New("unexpected server challenge")
	}

	switch {
	case bytes.Equal(fromServer, []byte("Username:")):
		return []byte(a.username), nil
	case bytes.Equal(fromServer, []byte("Password:")):
		return []byte(a.password), nil
	default:
		return nil, fmt.Errorf("unexpected server challenge: %s", fromServer)
	}
}

Thanks a lot!!!

Thank you for this!

Thank you

Microsoft has permanently disabled Basic Authentication in Exchange Online (Microsoft 365), you will receive the next message "Authentication unsuccessful, basic authentication is disabled".

Unfortunately this code no longer work, it's mandatory implement OAuth 2.0 or another method accepted by Microsoft