OAuth2

OAuth2 allows your application to store and use authentication tokens instead of actual login credentials. This is great for security as tokens or valid only for specific actions and can be easily revoked thus, once stolen, can’t to as much harm as actual account credentials. OAuth2 authentication in Nodemailer is mostly used with Gmail and G Suite (née Google Apps) even though there are other providers that support it as well.

Access Tokens needed for OAuth2 authentication are short lived so these need to be regenerated from time to time. Nodemailer is able to use both 3LO and 2LO to automatically regenerate the tokens but you can also handle all token specific yourself.

  1. Normal OAuth2 authentication
  2. Authenticating using Service Accounts
  3. Using custom token handling
  4. Token update notifications
  5. Examples
  6. Troubleshooting

Nodemailer requires an Access Token to perform authentication. 3-legged and 2-legged OAuth2 mechanisms are different ways to produce such tokens but in the end it does not matter how a token was exactly generated, as long as it is valid.

3-legged OAuth2 authentication

This is the “normal” way of obtaining access tokens. Your application requests permissions from the client and gets a refresh token in return that can be used to generate new access tokens.

  • auth – is the authentication object

    • type – indicates authentication type, set it to ‘OAuth2’
    • user – user email address (required)
    • clientId – is the registered client id of the application
    • clientSecret – is the registered client secret of the application
    • refreshToken – is an optional refresh token. If it is provided then Nodemailer tries to generate a new access token if existing one expires or fails
    • accessToken – is the access token for the user. Required only if refreshToken is not available and there is no token refresh callback specified
    • expires – is an optional expiration time for the current accessToken
    • accessUrl – is an optional HTTP endpoint for requesting new access tokens. This value defaults to Gmail

Normal SMTP transport (ie. not the pooled version) has a convenience method of using separate authentication for every message. This allows you to set up a transport with just clientId and clientSecret values and provide accessToken and refreshToken with the message options. See example 5.

2LO authentication (service accounts)

Nodemailer also allows you to use service accounts to generate access tokens. In this case the required auth options are a bit different from 3LO auth.

  • auth – is the authentication object

    • type – indicates authentication type, set it to ‘OAuth2’
    • user – user email address you want to send mail as (required)
    • serviceClient – service client id (required), you can find it from the “client_id” field in the service key file
    • privateKey – is the private key contents, you can find it from the “private_key” field in the service key file

Using custom token handling

If you do not want Nodemailer to create new access tokens then you can provide a custom token generation callback that is called every time a new token is needed for an user.

The registered function gets the following arguments:

  • user – is the user email address
  • renew – if true then previous access token either expired or it was not accepted by the SMTP server, in this case you should generate a new value
  • callback with arguments (err, accessToken) – is the callback function to run once you have generated a new access token
transporter.set('oauth2_provision_cb', (user, renew, callback)=>{
    let accessToken = userTokens[user];
    if(!accessToken){
        return callback(new Error('Unknown user'));
    }else{
        return callback(null, accessToken);
    }
});

Token update notifications

If you use refreshToken or service keys to generate new tokens from Nodemailer when accessToken is not present or expired then you can listen for the token updates by registering a ‘token’ event handler for the transporter object.

transporter.on('token', token => {
    console.log('A new access token was generated');
    console.log('User: %s', token.user);
    console.log('Access Token: %s', token.accessToken);
    console.log('Expires: %s', new Date(token.expires));
});

Examples

1. Authenticate using existing token

Use an existing Access Token. If the token is not accepted then message is not sent as there is no way to generate a new token.

let transporter = nodemailer.createTransport({
    host: 'smtp.gmail.com',
    port: 465,
    secure: true,
    auth: {
        type: 'OAuth2',
        user: '[email protected]',
        accessToken: 'ya29.Xx_XX0xxxxx-xX0X0XxXXxXxXXXxX0x'
    }
});

2. Custom handler

This example requests a new accessToken value from a custom OAuth2 handler. Nodemailer does not attempt to generate the token by itself.

let transporter = nodemailer.createTransport({
    host: 'smtp.gmail.com',
    port: 465,
    secure: true,
    auth: {
        type: 'OAuth2',
        user: '[email protected]'
    }
});

transporter.set('oauth2_provision_cb', (user, renew, callback)=>{
    let accessToken = userTokens[user];
    if(!accessToken){
        return callback(new Error('Unknown user'));
    }else{
        return callback(null, accessToken);
    }
});

3. Set up 3LO authentication

This example uses an existing Access Token. If the token is not accepted or current time is past the expires value, then refreshToken is used to automatically generate a new accessToken

let transporter = nodemailer.createTransport({
    host: 'smtp.gmail.com',
    port: 465,
    secure: true,
    auth: {
        type: 'OAuth2',
        user: '[email protected]',
        clientId: '000000000000-xxx0.apps.googleusercontent.com',
        clientSecret: 'XxxxxXXxX0xxxxxxxx0XXxX0',
        refreshToken: '1/XXxXxsss-xxxXXXXXxXxx0XXXxxXXx0x00xxx',
        accessToken: 'ya29.Xx_XX0xxxxx-xX0X0XxXXxXxXXXxX0x',
        expires: 1484314697598
    }
});

4. Set up 2LO authentication

This example uses an existing Access Token. If the token is not accepted or current time is past the expires value, then a new accessToken value is generated using provided service account.

let transporter = nodemailer.createTransport({
    host: 'smtp.gmail.com',
    port: 465,
    secure: true,
    auth: {
        type: 'OAuth2',
        user: '[email protected]',
        serviceClient: '113600000000000000000',
        privateKey: '-----BEGIN PRIVATE KEY-----\nMIIEvgIBADANBg...',
        accessToken: 'ya29.Xx_XX0xxxxx-xX0X0XxXXxXxXXXxX0x',
        expires: 1484314697598
    }
});

5. Provide authentication details with message options

This example demonstrates how to authenticate every message separately. This is mostly useful if you provide an email application that sends mail for multiple users. Instead of creating a new transporter for every message, create it just once and provide dynamic details with the message options.

Per-message specific authentication does not work in pooled mode

let transporter = nodemailer.createTransport({
    host: 'smtp.gmail.com',
    port: 465,
    secure: true,
    auth: {
        type: 'OAuth2',
        clientId: '000000000000-xxx.apps.googleusercontent.com',
        clientSecret: 'XxxxxXXxX0xxxxxxxx0XXxX0'
    }
});

transporter.sendMail({
    from: '[email protected]',
    to: '[email protected]',
    subject: 'Message',
    text: 'I hope this message gets through!',
    auth: {
        user: '[email protected]',
        refreshToken: '1/XXxXxsss-xxxXXXXXxXxx0XXXxxXXx0x00xxx',
        accessToken: 'ya29.Xx_XX0xxxxx-xX0X0XxXXxXxXXXxX0x',
        expires: 1484314697598
    }
});

Or alternatively you can do the same with your own OAuth2 handler.

let transporter = nodemailer.createTransport({
    host: 'smtp.gmail.com',
    port: 465,
    secure: true,
    auth: {
        type: 'OAuth2'
    }
});

transporter.set('oauth2_provision_cb', (user, renew, callback) => {
    let accessToken = userTokens[user];
    if(!accessToken){
        return callback(new Error('Unknown user'));
    }else{
        return callback(null, accessToken);
    }
});

transporter.sendMail({
    from: '[email protected]',
    to: '[email protected]',
    subject: 'Message',
    text: 'I hope this message gets through!',
    auth: {
        user: '[email protected]'
    }
});

Troubleshooting

  • The correct OAuth2 scope for Gmail SMTP is https://mail.google.com/, make sure your client has this scope set when requesting permissions for an user
  • Make sure that Gmail API access is enabled for your Client ID. To do this, search for the Gmail API in Google API Manager and click on “enable”