I have two urls, one for dev. env.: dev.moocapps and another for prod. env.: moocapps

I am trying to make the dev. env. just accessible for the software developers that are working with me, in this env. is running two cloud runs: one for front-end and another for back-end.

The front-end is communicating with a back-end (that is connecting to a database) and other external services (stripe, etc...)

The problem is that whenever I make the cloud run > Require authentication

I get the error:

Error: Forbidden
Your client does not have permission to get URL / from this server

What is the easiest way to make this development website just accessible for few people only?