Apache reverse proxy with basic authentication

You can follow the instructions here: Authentication, Authorization and Access Control. The main difference for your reverse proxy is that you’ll want to put the auth stuff inside a Location block, even though the docs say that they’re only allowed in Directory blocks:

<Location />
    AuthType Basic
    ...
</Location>

Outside the Location block you can put your proxy commands, such as:

ProxyPass / http://localhost:8080/