Refresh tokens are not returned by 0Auth2 client

[nwaltham]

Making a request using the following

var url = oauth2Client.generateAuthUrl({
    access_type : 'offline',
    scope : ['https://www.googleapis.com/auth/analytics.readonly https://www.googleapis.com/auth/analytics']
});

And in the call back:

  oauth2Client.getToken(code, function(err, tokens) {

results in a "tokens" object that does not have a refresh_token

[rakyll]

Refresh tokens are returned on the first exchange, you need to persist them permanently. The latter exchanges will only return an access token. In order to receive a new refresh token, revoke user's existing access token and go through the auth flow again.