feat: google wallet api authentication and authorization (#11)

Add utils class for google authentication

server/.env.local.sample

@@ -1,2 +1,7 @@
 BASIC_AUTH_USERNAME=username
 BASIC_AUTH_PASSWORD=password
+
+GOOGLE_APPLICATION_CREDENTIALS=
+GOOGLE_WALLET_ISSUER_ID=
+GOOGLE_WALLET_CLASS_ID=
+GOOGLE_WALLET_USER_ID=

server/utils/GoogleAuthUtils.ts

@@ -0,0 +1,28 @@
+const { GoogleAuth } = require('google-auth-library')
+const jwt = require('jsonwebtoken')
+
+export class GoogleAuthUtils {
+
+    static retrieveCredentials() {
+        console.log('retrieveCredentials')
+
+        // Path to service account key file obtained from Google CLoud Console.
+        const serviceAccountFile = process.env.GOOGLE_APPLICATION_CREDENTIALS || '/path/to/key.json'
+
+        // Issuer ID obtained from Google Pay Business Console.
+        const issuerId = process.env.GOOGLE_WALLET_ISSUER_ID || '<issuer ID>'
+
+        // Developer defined ID for the wallet class.
+        const classId = process.env.GOOGLE_WALLET_CLASS_ID || 'test-generic-class-id'
+
+        // Developer defined ID for the user, eg an email address.
+        const userId = process.env.GOOGLE_WALLET_USER_ID || '[email protected]'
+
+        // ID for the wallet object, must be in the form `issuerId.userId` where userId is alphanumeric.
+        const objectId = `${issuerId}.${userId.replace(/[^\w.-]/g, '_')}-${classId}`
+
+        const credentials = require(serviceAccountFile)
+
+        return credentials
+    }   
+}