Goole Sign for iOS or Android with offline access, server always get redirect_uri_mismatch

Question

I'm building a google sign flow with react-native using this lib https://github.com/devfd/react-native-google-signin/.

The lib works great, i can login with google successfully, but we need to ask for offline access to the api, there for the web app we use this flow. https://developers.google.com/identity/sign-in/web/server-side-flow.

And for the web works perfect, but when we try to do the same on the native app, we use the configuration for that in the react-native lib.

GoogleSignin.configure({
      webClientId: 'the client id of the backend server',
      iosClientId: 'the client id of the application',
      offlineAccess: true,
      forceConsentPrompt: true,
      scopes: [
        'https://www.googleapis.com/auth/userinfo.email',
        'https://www.googleapis.com/auth/plus.me',
        'https://www.googleapis.com/auth/gmail.readonly',
        'https://www.googleapis.com/auth/pubsub'
      ]
    })

From this we get a proper response from the lib, that include the:

serverAuthCode: <one-time token to access Google API from the backend on behalf of the user>

But when we try to exchange that code:

const google = require('googleapis');
const OAuth2 = google.auth.OAuth2;

const oauth2Client = new OAuth2(
  process.env.GOOGLE_CLIENT_ID,
  process.env.GOOGLE_CLIENT_SECRET,
  'postmessage'
);

export function getToken (code: string): Promise<any> {
  return new Promise((resolve, reject) => {
     oauth2Client.getToken(code, (err, tokens) => {
        if (!err) {
          resolve(tokens);
        } else {
          reject(err);
        }
      });
  });
}

I Always get and error of redirect_uri_mismatch or invalid_grant.

At this point i don't know what else i need to change. Maybe somebody know what is going on in here.

Answer 1

Ok, i found the solution. And is pretty easy.

When you use your ServerAuthCode in order to exchanged for a user token, you need to set your return URI on the backend equal to null.

This is what i did at the end with my getToken method. Now everything works like a charm!

export function getToken (code, typeOf = 'web') {
  const redirectUri = (typeOf === 'movil') ? null : 'postmessage';
  const oauth2Client = new OAuth2(
    process.env.GOOGLE_CLIENT_ID,
    process.env.GOOGLE_CLIENT_SECRET,
    redirectUri
  );
  return new Promise((resolve, reject) => {
     oauth2Client.getToken(code, (err, tokens) => {
        if (!err) {
          resolve(tokens);
        } else {
          reject(err);
        }
      });
  });
}