Support single page applications

Server hosting single page applications need to return index.html with a status code 200 when the requested file is not found.

There is an undocumented configuration option to serve Single Page Apps (SPA) today:

services:
  my_webapp:
    static:
      root: /var/www
      not_found:
        status: 200
        file: index.html

But I'm not 100% sure to like it as it is.

I was thinking about something like:

services:
  my_webapp:
    static:
      root: /var/www
      spa_mode: true

Any idea is welcome.