Add option to provide custom ssl certificates during development

Created by: alexbrazier

Closes: #4050 (closed) #3603 (closed) #3441 (closed) #1411 (closed)

This PR adds the option to provide a custom SSL certificate and key using the SSL_CRT_FILE and SSL_KEY_FILE env vars.

The webpack dev server already accepts certificates if you provide them, so this just reads the files and passes them in.

As an extra check so there is no confusion when an error occurs, it will verify the files exist and that they are valid before passing them into webpack.

You can pass in relative paths ../cert.crt, cert.crt etc, or full paths /Users/test/cert.crt

Testing

• Tested using yarn start and yarn create-react-app my-app
• Tested with .env file
• Tested with exported envs and inline envs
• Tested without HTTPS flag - (same behaviour as before)
• Tested with HTTPS flag and without new flags - (same behaviour as before)
• Tested with invalid path (see error below)
• Tested with invalid cert and key (see error below)
• Tested with valid custom cert and verified the dev server was using it

Invalid config errors

Doesn't exist

Invalid cert file