GAE: Google Account Authentication --a way to restrict access --DOING IT WITH YAML

NOTE: you can do this in code

To restrict access to your application in Google App Engine using Google Account Authentication, you can configure the app.yaml file to require login using the login directive under the handlers section.
If a URL does not have an authentication constraint, then anyone can access the URL, whether or not the client represents a signed-in user, and whether or not the app is set to use a members-only access policy.

Here’s how you can do it:

Example app.yaml Configuration for Google Account Authentication

runtime: nodejs14  # Specify your runtime environment

handlers:
                 - url: /.*
                 script: auto
                 login: required  # Requires users to log in with a Google Account
               

Explanation:

• login: required: This line specifies that users must log in with a Google Account to access the application. Google App Engine uses Google Sign-In as the authentication mechanism, allowing only authenticated Google users to access the app.

• login: optional: This option allows users to either log in or access the app without authentication.

• login: admin: Only users with administrative privileges (as defined in the Google Cloud project) can access the URL.

Optional: Restrict to Admin Users

To further restrict access to only admins, use the following in the YAML (app.yaml) file

handlers:
 - url: /.*
 script: auto
 login: admin  # Requires users to be administrators of the app
            

Line-by-Line Breakdown:

1. runtime: nodejs14

   • Purpose: Specifies the runtime environment that your application will use. In this case, it’s set to nodejs14, meaning your application is built using Node.js version 14. This tells Google App Engine which runtime to deploy and manage for your application.
   • Why it's important: The runtime field is required to let App Engine know how to handle your app, including configuring appropriate dependencies and services.

2. handlers:

   • Purpose: This section defines how incoming requests to your app are handled. Each handler specifies a URL pattern and how requests matching that pattern are processed. This is where you configure routing, static files, and other settings for your app's URLs.
   • Why it's important: Without the handlers section, App Engine won’t know what to do with incoming requests or how to apply the necessary restrictions for access control.

3. - url: /.*

   • Purpose: This line specifies the URL pattern to match for this handler. In this case, /. * is a regular expression that matches all URLs in your application (anything starting from the root /).
   • Why it's important: It tells Google App Engine that this handler should apply to all paths (e.g., /, /home, /about, etc.). It’s a way to ensure the entire app is protected under the access restrictions that follow.

4. script: auto

   • Purpose: This tells App Engine to automatically select the entry point for the application. In Node.js environments, this usually means starting the application by running npm start (defined in package.json), but App Engine will handle it for you based on the runtime environment.
   • Why it's important: This is a convenient shorthand to let App Engine figure out the correct script or entry point for your app without you needing to specify it explicitly in the app.yaml file.

5. login: required

   • Purpose: This line requires that any user who tries to access the application must first log in with their Google Account. If users are not authenticated, they will be redirected to the Google Sign-In page before they can access the content.
   • Why it's important: This enforces authentication, adding a layer of security to ensure that only authorized users (with Google Accounts) can access your app. Without this, your app would be publicly accessible by default.

Key Variations for login

• login: required: Enforces that all users must sign in with their Google Account before accessing the application. Suitable for apps where you want to restrict access to only authenticated users.

• login: optional: Allows users to access the application either with or without signing in. This is useful for apps that have both public and user-specific content.

• login: admin: Restricts access only to users who are administrators of the Google Cloud project. Only these users will be allowed to access the URLs that match the handler. This is commonly used for admin dashboards or sensitive areas of the app.

Resources:

1. Restricting User Access in App Engine - Google Cloud Documentation:
   https://cloud.google.com/appengine/docs/standard/nodejs/config/appref#handlers_element
2. Google Account Authentication with App Engine - Google Cloud Documentation:
   https://cloud.google.com/appengine/docs/standard/python/users