Domain-wide delegation using default credentials in Google Cloud Run - node.js

Question

I'm using a custom service account (using --service-account parameter in the deploy command). That service account has domain-wide delegation enabled and it's installed in the G Apps Admin panel.
I tried this code:
app.get('/test', async (req, res) => {
const auth = new google.auth.GoogleAuth()
const gmailClient = google.gmail({ version: 'v1' })
const { data } = await gmailClient.users.labels.list({ auth, userId: 'user#domain.com' })
return res.json(data).end()
})
It works if I run it on my machine (having the GOOGLE_APPLICATION_CREDENTIALS env var setted to the path of the same service account that is assigned to the Cloud Run service) but when it's running in Cloud Run, I get this response:
{
"code" : 400,
"errors" : [ {
"domain" : "global",
"message" : "Bad Request",
"reason" : "failedPrecondition"
} ],
"message" : "Bad Request"
}
I saw this solution for this same issue, but it's for Python and I don't know how to replicate that behaviour with the Node library.

Answer 1

After some days of research, I finally got a working solution (porting the Python implementation):
async function getGoogleCredentials(subject: string, scopes: string[]): Promise<JWT | OAuth2Client> {
const auth = new google.auth.GoogleAuth({
scopes: ['https://www.googleapis.com/auth/cloud-platform'],
})
const authClient = await auth.getClient()
if (authClient instanceof JWT) {
return (await new google.auth.GoogleAuth({ scopes, clientOptions: { subject } }).getClient()) as JWT
} else if (authClient instanceof Compute) {
const serviceAccountEmail = (await auth.getCredentials()).client_email
const unpaddedB64encode = (input: string) =>
Buffer.from(input)
.toString('base64')
.replace(/=*$/, '')
const now = Math.floor(new Date().getTime() / 1000)
const expiry = now + 3600
const payload = JSON.stringify({
aud: 'https://accounts.google.com/o/oauth2/token',
exp: expiry,
iat: now,
iss: serviceAccountEmail,
scope: scopes.join(' '),
sub: subject,
})
const header = JSON.stringify({
alg: 'RS256',
typ: 'JWT',
})
const iamPayload = `${unpaddedB64encode(header)}.${unpaddedB64encode(payload)}`
const iam = google.iam('v1')
const { data } = await iam.projects.serviceAccounts.signBlob({
auth: authClient,
name: `projects/-/serviceAccounts/${serviceAccountEmail}`,
requestBody: {
bytesToSign: unpaddedB64encode(iamPayload),
},
})
const assertion = `${iamPayload}.${data.signature!.replace(/=*$/, '')}`
const headers = { 'content-type': 'application/x-www-form-urlencoded' }
const body = querystring.encode({ assertion, grant_type: 'urn:ietf:params:oauth:grant-type:jwt-bearer' })
const response = await fetch('https://accounts.google.com/o/oauth2/token', { method: 'POST', headers, body }).then(r => r.json())
const newCredentials = new OAuth2Client()
newCredentials.setCredentials({ access_token: response.access_token })
return newCredentials
} else {
throw new Error('Unexpected authentication type')
}
}

Answer 2

What you can do here is define ENV variables in your yaml file as described in this documentation to set the GOOGLE_APPLICATION_CREDENTIALS to the path of the JSON key.
Then use a code such as the one mentioned here.
const authCloudExplicit = async ({projectId, keyFilename}) => {
// [START auth_cloud_explicit]
// Imports the Google Cloud client library.
const {Storage} = require('#google-cloud/storage');
// Instantiates a client. Explicitly use service account credentials by
// specifying the private key file. All clients in google-cloud-node have this
// helper, see https://github.com/GoogleCloudPlatform/google-cloud-node/blob/master/docs/authentication.md
// const projectId = 'project-id'
// const keyFilename = '/path/to/keyfile.json'
const storage = new Storage({projectId, keyFilename});
// Makes an authenticated API request.
try {
const [buckets] = await storage.getBuckets();
console.log('Buckets:');
buckets.forEach(bucket => {
console.log(bucket.name);
});
} catch (err) {
console.error('ERROR:', err);
}
// [END auth_cloud_explicit]
};
Or follow an approach similar to the one mentioned here.
'use strict';
const {auth, Compute} = require('google-auth-library');
async function main() {
const client = new Compute({
serviceAccountEmail: 'some-service-account#example.com',
});
const projectId = await auth.getProjectId();
const url = `https://dns.googleapis.com/dns/v1/projects/${projectId}`;
const res = await client.request({url});
console.log(res.data);
}
main().catch(console.error);