How to get refresh token while using Google API JS Client

Question

I have been trying to implement an app that would need user to grant access to Google Analytics. I have been following this tutorial:

https://developers.google.com/analytics/solutions/articles/hello-analytics-api

And at some other places there is code for AngularJs which uses the same functionL

https://gist.github.com/jakemmarsh/5809963

My problem is, that the auth works pretty well, but it does not return a refresh_token. It never returns a refresh_token. I have tried all the possible available on the web. 1. The first time, 2. Using prompt=force etc etc.. But nothing seems to return the refresh_token. I guess that part is skipped by the client or something.

I need to know how can I get the refresh_token when the user grants access for the first time so that I can save it.

Answer 1

It does not return a refresh token as designed. The tutorial and the code you mentioned are using Google APIs Client Library for JavaScript. This library uses the OAuth 2.0 client-side flow for making requests that require authorization.

As The OAuth 2.0 Authorization Framework says:

The implicit grant type is used to obtain access tokens (it does not support the issuance of refresh tokens) and is optimized for public clients known to operate a particular redirection URI. These clients are typically implemented in a browser using a scripting language such as JavaScript.

In fact, The authorization code flow is the only one which issue refresh token, and Google supports this flow in these Scenarios: Web server applications, Installed applications, and Applications on limited-input devices, but not Client-side (JavaScript) applications or Service accounts. Get more details from here.

So you'll not get refresh token in this way.

Answer 2

Not sure if this is the right way, but I'm able to get a refresh token using the following code:

window.gapi.client.init({
  apiKey: this.GOOGLE.API_KEY,
  clientId: this.GOOGLE.CLIENT_ID,
  discoveryDocs: DISCOVERY_DOCS,
  scope: SCOPES
}).then(()=>{
  const authInstance = window.gapi.auth2.getAuthInstance();
  authInstance.grantOfflineAccess()
   .then((res) => {
      console.log(res);
      this.data.refreshToken = res.code;
   });
});