gmail

README

Summary

Provide permission to Thunderbird to access my Gmail details.

Use dev tools in Thunderbird to read the client_id and secret used to generate tokens.

Enable smtp console debug to check how the protocol works and how the credentials are combined and sent to smtp.gmail.com

Implement the protocol in Go

Details

Accoutn setup

Thunderbird will automatically download the IMAP and SMTP (SSL/TLS) settings for my Gmail account.

Authoriza app

Thunderbird redirects me to accounts.google.com so I can get authenticated, and give it permission to send emails on my behalf.

Thunderbird debug

• Access dev tools on Thunderbird to see network requests and console logs

• Increase the log level for mailnews.smtp.loglevel (https://wiki.mozilla.org/MailNews:Logging)

• Send an email to capture an OAUTH2 authentication to Google.

• Check the browser console for SMTP message exchange. Click on SmtpClient.jsm to look at the suppressed logs.

• Add a breaking point to read the value of the variable suppressed in the logs in the current scope.

• Base64 decode the token, and print the byte value of the result (fields are separated and terminated with Control+A: \001)

$ echo "dXNlcj1nYX[]...]MTcxAQE=" | base64 -d | xxd -c 32
00000000: 7573 6572 3d67 6172 6369 616f 6b65 6c6c 7964 6176 6973 6d40 676d 6169 6c2e 636f  user=garciaokellydavism@gmail.co
00000020: 6d01 6175 7468 3d42 6561 7265 7220 7961 3239 2e61 3041 6435 324e 335f 4c6d 6547  m.auth=Bearer ya29.a0Ad52N3_LmeG
[...]
000000e0: 5953 4152 4153 4651 4847 5832 4d69 3133 4745 5944 354e 6c7a 6676 757a 3874 5739  YSARASFQHGX2Mi13GEYD5Nlzfvuz8tW9
00000100: 314e 4651 3031 3731 0101                                                         1NFQ0171..

The format is documented in: https://developers.google.com/gmail/imap/xoauth2-protocol#initial_client_response

Implement in Go

[...]
// Create a TLS connection
	conn, err := tls.Dial("tcp", "smtp.gmail.com:465", &tls.Config{
		InsecureSkipVerify: true,
	})
// Create a new SMTP client passing the existing connection 
	cli, err := smtp.NewClient(conn, "smtp.gmail.com")
// Say Hi
	err = cli.Hello("localhost")
// Authenticate with our authenticator 
	err = cli.Auth(&GoogleAuth{})
[...]


// Authenticator methods 
func (ga *GoogleAuth) Start(server *smtp.ServerInfo) (string, []byte, error) {
	// OAUTH details
	host := "https://www.googleapis.com/oauth2/v3/token"

// Request a token with Thunderbird's client id and secret 
	resp, err := http.PostForm(host, url.Values{
		"client_id": {
			cfg.ClientID,
		},
		"client_secret": {
			cfg.ClientSecret,
		},
		"grant_type": {
			"refresh_token",
		},
		"refresh_token": {
			cfg.RefreshToken,
		},
	})
[...]

// Return the Credentials including user and token with x01 as separator 
return "XOAUTH2", []byte("user=" + cfg.Mail + "\x01" + "auth=Bearer " + google_token.Token + "\x01\x01"), nil
}

Documentation

Index

• func Send()
• type GoogleAuth
  • func (ga *GoogleAuth) Next(fromServer []byte, more bool) (toServer []byte, err error)
  • func (ga *GoogleAuth) Start(server *smtp.ServerInfo) (string, []byte, error)
• type GoogleConfig

Functions

func Send

func Send()

Types

type GoogleAuth

type GoogleAuth struct{}

func (*GoogleAuth) Next

func (ga *GoogleAuth) Next(fromServer []byte, more bool) (toServer []byte, err error)

func (*GoogleAuth) Start

func (ga *GoogleAuth) Start(server *smtp.ServerInfo) (string, []byte, error)

type GoogleConfig

type GoogleConfig struct {
	Mail         string `json:"mail"`
	ClientID     string `json:"client_id"`
	ClientSecret string `json:"client_secret"`
	RefreshToken string `json:"refresh_token"`
}