Secure React App deployed on Heroku

I'm working on a rapid prototype using React. As you would expect, I created the app using the command
create-react-app my-app
I then checked this in and deployed the app to Heroku. I'm using create-react-app-buildpack to create the static pages for Heroku to serve.

I would now like to secure the app so only the people developing the app can see it. Basic HTTP Authentication would be fine, or anything else really as long as I don't need any server-side code to do it. The server-side code will most likely end up being Node.js or AWS Lambdas.

I did notice that Heroku seems to be using Nginx but I don't know if I have access to the config files or where they are.

Any help with this would be greatly appreciated.

via TheLukeMcCarthy