How to debug invalid_grant during authorization code exchange? - google-oauth

Question

My application is using OAuth to access the Youtube Data API. My OAuth callback is written in node and uses the OAuth2Client class from the "googleapis" npm package to exchange the authorization code for the access and refresh tokens.
Everything was working fine up to last week until suddenly I started getting the "invalid_grant" response during the authorization code exchange. I have tried everything to resolve this and am running out of ideas. My callback executes as a cloud function so I don't think that it would be out of sync with NTP.
My OAuth consent screen is in "Testing" mode and my email address is included in the test users. The odd thing is that even though the authorization code exchange fails, my Google account's "Third-party apps with account access" section lists my application as if the handshake succeeded.
Here is my code for generating the auth URL and exchanging the authorization code. The invalid_grant occurs during the call to "oauth2.getToken"
async startFlow(scopes: string[], state: string): Promise<AuthFlow> {
const codes = await oauth2.generateCodeVerifierAsync();
const href = oauth2.generateAuthUrl({
scope: scopes,
state,
access_type: 'offline',
include_granted_scopes: true,
prompt: 'consent',
code_challenge_method: CodeChallengeMethod.S256,
code_challenge: codes.codeChallenge
});
return { href, code_verifier: codes.codeVerifier };
}
async finishFlow(code: string, verifier: string): Promise<Tokens> {
const tokens = await oauth2.getToken({ code, codeVerifier: verifier })
return {
refresh_token: tokens.tokens.refresh_token!,
access_token: tokens.tokens.access_token!,
expires_in: tokens.tokens.expiry_date!,
token_type: 'Bearer',
scopes: tokens.tokens.scope!.split(' ')
};
}
"oauth2" is an instance of OAuth2Client from "google-auth-library". I initialize it here:
export const oauth2 = new google.auth.OAuth2({
clientId: YT_CLIENT_ID,
clientSecret: YT_CLIENT_SECRET,
redirectUri: `${APP_URI}/oauth`
});
Looking at the logs, the only out of the ordinary thing I notice is that the application/x-www-form-urlencoded body looks slightly different than the example https://developers.google.com/identity/protocols/oauth2/web-server#exchange-authorization-code
The POST request to "https://oauth2.googleapis.com/token" ends up looking like this:
code=4%2F0AX4XfWiKHVnsavUH7en0TywjPJVRyJ9aGN-JR8CAAcAG7dT-THxyWQNcxd769nzaHLUb8Q&client_id=XXXXXXXXXX-XXXXXXXXXXXXXXX.apps.googleusercontent.com&client_secret=XXXXXX-XXXXXXXXXXXXXXX-XX_XXX&redirect_uri=https%3A%2F%2Fapp.example.com%2Foauth&grant_type=authorization_code&code_verifier=KjOBmr4D9ISLPSE4claEBWr3UN-bKdPHZa8BBcQvcmajfr9RhWrgt7G429PLEpsP7oGzFGnBICu3HgWaHPsLhMkGBuQ2GmHHiB4OpY2F0rJ06wkpCjV2cCTDdpfRY~Ej
Notice that the "/" characters are not percent-encoded in the official example, but they are in my requests. Could this actually be the issue? I don't see how the official google auth library would have an issue this large.

Answer 1

If you check the documentation on expiration of refresh tokens you will see
A Google Cloud Platform project with an OAuth consent screen configured for an external user type and a publishing status of "Testing" is issued a refresh token expiring in 7 days.
Set your project to production mode and your refresh tokens will last longer then a week.
library
IMO if your refresh token expires your library should be requesting access again. However the library was created before the change that a refresh token gets revoked. This isnt a true refresh token expired error message and the library isn't detecting that.
A post over on the issue forum for your library may encourage them to patch it so that it is more obvious of an error message.
At any rate you need to delete the stored tokens for that user which will request authorization again.
update If its not that.
ensure that your computer / server has the correct time
revoke the users access directly via their google account. Under third party apps with access ensure that your app isnt listed if it is remove it.
Make sure that you are using the correct client type from google developer console.
Google node.js sample
var fs = require('fs');
var readline = require('readline');
var {google} = require('googleapis');
var OAuth2 = google.auth.OAuth2;
// If modifying these scopes, delete your previously saved credentials
// at ~/.credentials/youtube-nodejs-quickstart.json
var SCOPES = ['https://www.googleapis.com/auth/youtube.readonly'];
var TOKEN_DIR = (process.env.HOME || process.env.HOMEPATH ||
process.env.USERPROFILE) + '/.credentials/';
var TOKEN_PATH = TOKEN_DIR + 'youtube-nodejs-quickstart.json';
// Load client secrets from a local file.
fs.readFile('client_secret.json', function processClientSecrets(err, content) {
if (err) {
console.log('Error loading client secret file: ' + err);
return;
}
// Authorize a client with the loaded credentials, then call the YouTube API.
authorize(JSON.parse(content), getChannel);
});
/**
* Create an OAuth2 client with the given credentials, and then execute the
* given callback function.
*
* #param {Object} credentials The authorization client credentials.
* #param {function} callback The callback to call with the authorized client.
*/
function authorize(credentials, callback) {
var clientSecret = credentials.installed.client_secret;
var clientId = credentials.installed.client_id;
var redirectUrl = credentials.installed.redirect_uris[0];
var oauth2Client = new OAuth2(clientId, clientSecret, redirectUrl);
// Check if we have previously stored a token.
fs.readFile(TOKEN_PATH, function(err, token) {
if (err) {
getNewToken(oauth2Client, callback);
} else {
oauth2Client.credentials = JSON.parse(token);
callback(oauth2Client);
}
});
}
/**
* Get and store new token after prompting for user authorization, and then
* execute the given callback with the authorized OAuth2 client.
*
* #param {google.auth.OAuth2} oauth2Client The OAuth2 client to get token for.
* #param {getEventsCallback} callback The callback to call with the authorized
* client.
*/
function getNewToken(oauth2Client, callback) {
var authUrl = oauth2Client.generateAuthUrl({
access_type: 'offline',
scope: SCOPES
});
console.log('Authorize this app by visiting this url: ', authUrl);
var rl = readline.createInterface({
input: process.stdin,
output: process.stdout
});
rl.question('Enter the code from that page here: ', function(code) {
rl.close();
oauth2Client.getToken(code, function(err, token) {
if (err) {
console.log('Error while trying to retrieve access token', err);
return;
}
oauth2Client.credentials = token;
storeToken(token);
callback(oauth2Client);
});
});
}
/**
* Store token to disk be used in later program executions.
*
* #param {Object} token The token to store to disk.
*/
function storeToken(token) {
try {
fs.mkdirSync(TOKEN_DIR);
} catch (err) {
if (err.code != 'EEXIST') {
throw err;
}
}
fs.writeFile(TOKEN_PATH, JSON.stringify(token), (err) => {
if (err) throw err;
console.log('Token stored to ' + TOKEN_PATH);
});
}
/**
* Lists the names and IDs of up to 10 files.
*
* #param {google.auth.OAuth2} auth An authorized OAuth2 client.
*/
function getChannel(auth) {
var service = google.youtube('v3');
service.channels.list({
auth: auth,
part: 'snippet,contentDetails,statistics',
forUsername: 'GoogleDevelopers'
}, function(err, response) {
if (err) {
console.log('The API returned an error: ' + err);
return;
}
var channels = response.data.items;
if (channels.length == 0) {
console.log('No channel found.');
} else {
console.log('This channel\'s ID is %s. Its title is \'%s\', and ' +
'it has %s views.',
channels[0].id,
channels[0].snippet.title,
channels[0].statistics.viewCount);
}
});
}

Answer 2

I've discovered my problem. Another part of my code was throwing an error while the authorization request was being sent (some weird async code). This caused the request to bail halfway through and send only a partial body. This resulted in the invalid_grant appearing in my logs which misled me to believe this was the root cause of my problem.
I fixed the other piece of my code and now the authorization request succeeds without issue.