header {
    # CSP limits which features can be used. By default we allow nothing and only allow required options. See https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/Content-Security-Policy
    # default-src 'none'; Allow nothing by default
    # script-src-elem/style-src-elem 'self'; Only allow loading css/js files from same origin (AIO itself) while blocking all inline css/js
    # img-src 'self'; Only allow loading images from same origin (from AIO itself)
    # connect-src 'self'; Allow fetch to only connect same origin (to AIO itself)
    # frame-src 'self'; Allow AIO to only embed itself "what can be embedded"
    # base-uri 'none'; This does not fallback to default-src, AIO does not use the html base tag
    # form-action 'self'; Html forms are only allowed to submit to AIO and not cross origin
    # frame-ancestors 'self'; Only allow AIO itself to embed it self "who can embed"
    # upgrade-insecure-requests; Upgrade all http embedings to https
    # require-trusted-types-for 'script'; trusted-types 'none'; Blocks DOM changes via js
    Content-Security-Policy "default-src 'none'; script-src-elem 'self'; style-src-elem 'self'; img-src 'self'; connect-src 'self'; frame-src 'self'; base-uri 'none'; form-action 'self'; frame-ancestors 'self'; upgrade-insecure-requests; require-trusted-types-for 'script'; trusted-types 'none';"
    X-Content-Type-Options "nosniff" # This forces the browser to use the MIME type of the Content-Type header. See https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/X-Content-Type-Options
    X-Frame-Options "SAMEORIGIN" # Only allow AIO itself to embed itself, this is also enforced as part of the CSP frame-ancestors. See https://developer.mozilla.org/de/docs/Web/HTTP/Reference/Headers/X-Frame-Options
    X-Permitted-Cross-Domain-Policies "none" # We block all cross origin request, including ones from Adobe Acrobat or Microsoft Silverlight and Adobe Flash Player. See https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/X-Permitted-Cross-Domain-Policies
    X-DNS-Prefetch-Control "off" # Tells the browser to not pre-fetch the DNS of linked pages. See https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/X-DNS-Prefetch-Control
    Referrer-Policy "no-referrer" # Tells the browser to never sent a Referer header. See https://developer.mozilla.org/de/docs/Web/HTTP/Reference/Headers/Referrer-Policy
    X-Robots-Tag "noindex, nofollow" # Tells web crawlers to not index this page. See https://developer.mozilla.org/de/docs/Web/HTTP/Reference/Headers/X-Robots-Tag
    Origin-Agent-Cluster "?1" # Isolates AIO from other same site pages. See https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/Origin-Agent-Cluster
    Cross-Origin-Opener-Policy "same-origin"; # AIO does not use any popup, still we can isolate its BCG if it is opened as a pop up by another page. See https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/Cross-Origin-Opener-Policy
    Cross-Origin-Embedder-Policy "require-corp"; # Harder rules for cross origin embeds. See https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/Cross-Origin-Embedder-Policy
    Cross-Origin-Resource-Policy "same-origin"; # Only allow the same origin to load resources. See https://developer.mozilla.org/en-US/docs/Web/HTTP/Guides/Cross-Origin_Resource_Policy

    # Permissions-Policy disables browser features that AIO does not use. Since there is no "deny all" option, all known features need to be listed explicitly. See https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/Permissions-Policy
    Permissions-Policy "accelerometer=(), ambient-light-sensor=(), aria-notify=(), attribution-reporting=(), autoplay=(), battery=(), bluetooth=(), browsing-topics=(), camera=(), captured-surface-control=(), ch-ua-high-entropy-values=(), compute-pressure=(), cross-origin-isolated=(), deferred-fetch=(), deferred-fetch-minimal=(), display-capture=(), document-domain=(), encrypted-media=(), execution-while-not-rendered=(), execution-while-out-of-viewport=(), fullscreen=(), gamepad=(), geolocation=(), gyroscope=(), hid=(), identity-credentials-get=(), idle-detection=(), language-detector=(), local-fonts=(), magnetometer=(), microphone=(), midi=(), on-device-speech-recognition=(), otp-credentials=(), payment=(), picture-in-picture=(), private-state-token-issuance=(), private-state-token-redemption=(), publickey-credentials-create=(), publickey-credentials-get=(), screen-wake-lock=(), serial=(), speaker-selection=(), storage-access=(), summarizer=(), translator=(), usb=(), web-share=(), window-management=(), xr-spatial-tracking=()"

    -Server
    -X-Powered-By
    -Via
}