How do I setup Digital Ocean’s static sites with custom headers, like “Referrer-Policy”?

Netlify let’s you set custom headers for static sites by adding to their TOML file:

[[headers]]
  for = "/*"
  [headers.values]
    Referrer-Policy = "no-referrer"
    X-Content-Type-Options = "nosniff"
    X-Frame-Options = "deny"
    X-XSS-Protection = "1; mode=block"

What’s the equivalent for an app spec on Digital Ocean?