How to resolve Nodejs google-auth-library invalid token signature error? - node.js

Question

I'm using flutter for my mobile app. I try to add sign in with google. Everything is okay for Flutter side. I'm gettin idToken from mobile app and send to my backend, nodejs.
Now, I want to use this idToken to authenticate user's requests on nodejs backend side with google-auth-library package.
let token = "token"
const CLIENT_ID = "client_id"
const { OAuth2Client } = require('google-auth-library');
const client = new OAuth2Client(CLIENT_ID);
async function verify() {
try {
const ticket = await client.verifyIdToken({
idToken: token,
audience: CLIENT_ID, // Specify the CLIENT_ID of the app that accesses the backend
// Or, if multiple clients access the backend:
//[CLIENT_ID_1, CLIENT_ID_2, CLIENT_ID_3]
});
const payload = ticket.getPayload();
const userid = payload['sub'];
console.log(payload)
} catch (error) {
console.log(error)
}
}
verify()
But this code always returns this error => Error: Invalid token signature:
at OAuth2Client.verifySignedJwtWithCertsAsync (\node_modules\google-auth-library\build\src\auth\oauth2client.js:566:19)
What should I do for to verify this idToken on nodejs backend side?
Thanks.

Answer 1

If the idToken that you are passing to the function is from the log of your flutter app, it is likely that you are not getting the entire idToken printed in the log due to the limitations of print().
I used the below code snippet to print out the idToken and used that in the API which gave me a success response.
print('ID TOKEN');
String token = googleAuth.idToken;
while (token.length > 0) {
int initLength = (token.length >= 500 ? 500 : token.length);
print(token.substring(0, initLength));
int endLength = token.length;
token = token.substring(initLength, endLength);
}