related to #8031, this adds the following headers to HTML responses:
- Strict-Transport-Security: informs browsers that the site should only
be accessed using HTTPS, and that any future attempts to access it
using HTTP should automatically be converted to HTTPS.
- X-Frames-Options: disallows embedding the UI in other sites via
<frame>, <iframe>, <embed> or <object>, which can prevent attacks like
clickjacking.
- X-Content-Type-Options: prevents browsers from trying to guess the MIME
type which can cause browsers to transform non-executable content into
executable content.
- Referrer-Policy: prevents leaking the origin of the referrer in the
Referer.
additionally, this ensures we set `X-Content-Type-Options` for CSV and
installer responses.
Related to #6894, this entirely replaces FLEET_DEMO with the server config added in #6597
As part of this, I also implemented a small refactor to the integration test suite to allow setting a custom config when the server is initialized.
