A web design company has moved all client sites to Google App Engine. Some sites are still under development and should only be accessible to customers and company employees from any location. What is the solution to restrict access to these in-progress sites?

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Upload an .htaccess file containing the customer and employee user accounts to App Engine.

Create an App Engine firewall rule that allows access from the customer and employee networks and denies all other traffic.

Enable Cloud Identity-Aware Proxy (IAP), and allow access to a Google Group that contains the customer and employee user accounts.

Use Cloud VPN to create a VPN connection between the relevant on-premises networks and the company's GCP Virtual Private Cloud (VPC) network.

Google Professional Cloud Security Engineer