GCP Secret Manager to get runtime environment credentials for multiple environments

db.ts

import {SecretManagerServiceClient} from '@google-cloud/secret-manager';
import * as admin from 'firebase-admin';

const client = new SecretManagerServiceClient();

let credentials: admin: admin.app.App;
let credentials1: admin: admin.app.App;
let credentials2: admin: admin.app.App;

export const db = async (type: string): Promise<admin: admin.app.App> => {
    switch (type) {
        case 'credentials':
            if (credentials) {
                return credentials;
            } else {
                credentials = await getCredential(process.env.C1, type);
                return credentials;
            }
        case 'credentials1':
            if (credentials1) {
                return credentials1;
            } else {
                credentials1 = await getCredential(process.env.C2, type);
                return credentials1;
            }
        case 'credentials2':
             if (credentials2) {
                return credentials2;
            } else {
                credentials2 = await getCredential(process.env.C3, type);
                return credentials2;
            }
    }
};

async function getCredential(path: string, type: string): Promise<admin: admin.app.App> {
    try {
        const tempCredential: admin: admin.app.App;
        const [version] = await client.accessSecretVersion({
            name: path,
        });
        const result: any = JSON.parse(version.payload.data.toString());
        const params = {
            type: result.type,
            projectId: result.project_id,
            privateKeyId: result.private_key_id,
            privateKey: result.private_key,
            clientEmail: result.client_email,
            clientId: result.client_id,
            authUri: result.auth_uri,
            tokenUri: result.token_uri,
            authProviderX509CertUrl: result.auth_provider_x509_cert_url,
            clientC509CertUrl: result.client_x509_cert_url,
        };
        tempCredential.admin = admin.initializeApp({
            credential: admin.credential.cert(params),
            storageBucket: `gs://${result.project_id}.appspot.com`,
        }, type);
        return tempCredential;
    } catch (e) {
        console.error('credentials error. Check if the app engine default service account has scret manager accessor' +
            ' access', e);
        return null;
    }
}