GCP Consume a REST API after OAuth in Node.js - node.js

Question

I am working to implement a Node.js webapp to be deployed on GCP App Engine.
Following the Node.js Bookshelf App sample, I did manage to implement a basic user authentication flow using the passport-google-oauth20 and retrieve basic profile information. I basically just got rid of what was not needed for my purposes
My custom code is available at: gist.github.com/vdenotaris/3a6dcd713e4c3ee3a973aa00cf0a45b0.
However, I would now like to consume a GCP Cloud Storage API to retrieve all the storage objects within a given buckets with the logged identity.
This should be possible by:
adding a proper scope for the request.
authenticating the REST requests using the user session token obtained via OAuth.
About the post-auth handler, the documentation says:
After you obtain credentials, you can store information about the
user. Passport.js automatically serializes the user to the session.
After the user’s information is in the session, you can make a couple
of middleware functions to make it easier to work with authentication.
// Middleware that requires the user to be logged in. If the user is not logged
// in, it will redirect the user to authorize the application and then return
// them to the original URL they requested.
function authRequired (req, res, next) {
if (!req.user) {
req.session.oauth2return = req.originalUrl;
return res.redirect('/auth/login');
}
next();
}
// Middleware that exposes the user's profile as well as login/logout URLs to
// any templates. These are available as `profile`, `login`, and `logout`.
function addTemplateVariables (req, res, next) {
res.locals.profile = req.user;
res.locals.login = `/auth/login?return=${encodeURIComponent(req.originalUrl)}`;
res.locals.logout = `/auth/logout?return=${encodeURIComponent(req.originalUrl)}`;
next();
}
But I do not see where the token is stored, how can I retrieve it and how to use it to consume a web-service (in my case, GCP storage).
I am not at all a node.js expert, so it would be nice having a bit more clarity on that: could someone explain me how to proceed in consuming a REST API using the logged user credentials (thus IAM/ACL privileges)?

Answer 1

If you want to access Cloud Storage through the use of a token obtained with OAuth, when the application requires user data, it will prompt a consent screen, asking for the user to authorize the app to get some of their data. If the user approves, an access token is generated, which can be attached to the user's request. This is better explained here.
If you plan to run your application in Google App Engine, there will be a service account prepared with the necessary authentication information, so no further setup is required. You may need to generate the service account credentials (generally in JSON format), that have to be added to the GOOGLE_APPLICATION_CREDENTIALS environment variable in gcloud.
Here is an example of how to authenticate and consume a REST API with the token that was obtained in the previous step. This, for example, would be a request to list objects stored in a bucket:
GET /storage/v1/b/example-bucket/o HTTP/1.1
Host: www.googleapis.com
Authorization: Bearer [YOUR_TOKEN]