fix: Make ADC + human account work with firebase-admin

[foxrafa]

This PR is intended to fix a current bug in firebase-admin.

Google Cloud recommends utilizing [Application Default Credentials (ADC)] (https://cloud.google.com/docs/authentication/application-default-credentials), however this feature does not fully work with the firebase-admin-node library when you want to utilize a human account (person@domain.com) instead of a service account.

Some GCP APIs require you to specify the quota project associated to the request, however, the current implementation of the firebase-admin-node library does not provide the project ID when making requests to GCP APIs, even if you set them through gcloud auth application-default set-quota-project YOUR_PROJECT, because the code that handles the requests never adds the project ID to the request. And you get errors like this:

Your application is authenticating by using local Application Default Credentials. The identitytoolkit.googleapis.com API requires a quota project, which is not set by default. To learn how to set your quota project, see https://cloud.google.com/docs/authentication/adc-troubleshooting/user-creds .

Therefore, this pull request aims to fix this issue by checking if a projectId was provided when calling the initializeApp() function and adds it to the x-goog-user-project header of requests made to GCP APIs, just like the documentation states it should be set.

This implementation is similar to how the (working) google-auth-library library handles ADC authentication (src/auth/authclient.ts:270):

    /**
     * Append additional headers, e.g., x-goog-user-project, shared across the
     * classes inheriting AuthClient. This method should be used by any method
     * that overrides getRequestMetadataAsync(), which is a shared helper for
     * setting request information in both gRPC and HTTP API calls.
     *
     * @param headers object to append additional headers to.
     */
    addSharedMetadataHeaders(headers) {
        // quota_project_id, stored in application_default_credentials.json, is set in
        // the x-goog-user-project header, to indicate an alternate account for
        // billing and quota:
        if (!headers['x-goog-user-project'] && // don't override a value the user sets.
            this.quotaProjectId) {
            headers['x-goog-user-project'] = this.quotaProjectId;
        }
        return headers;
    }

This should also solve some problems described in #1377

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[lahirumaramba]

LGTM! Thank you!

[lahirumaramba]

Hi @foxrafa could you please take a look at the lint errors in the failing CIs? Thanks!

[foxrafa]

@lahirumaramba fixed it.

[foxrafa]

Oh, all of the test cases are not expecting the x-goog-user-project header. Can I change them @lahirumaramba ?

[lahirumaramba]

@lahirumaramba fixed it.

Thanks! We also need to update the unit tests :)

[foxrafa]

@lahirumaramba fixed it.

Thanks! We also need to update the unit tests :)

I updated them now.

[rogsilva]

When will a new version with this change be released?

[foxrafa]

@lahirumaramba any ETA on when this fix will be generally available?