view tests/sslcerts/client-cert.pem @ 30766:d7bf7d2bd5ab

hgweb: support Content Security Policy

Content-Security-Policy (CSP) is a web security feature that allows
servers to declare what loaded content is allowed to do. For example,
a policy can prevent loading of images, JavaScript, CSS, etc unless
the source of that content is whitelisted (by hostname, URI scheme,
hashes of content, etc). It's a nifty security feature that provides
extra mitigation against some attacks, notably XSS.

Mitigation against these attacks is important for Mercurial because
hgweb renders repository data, which is commonly untrusted. While we
make attempts to escape things, etc, there's the possibility that
malicious data could be injected into the site content. If this happens
today, the full power of the web browser is available to that
malicious content. A restrictive CSP policy (defined by the server
operator and sent in an HTTP header which is outside the control of
malicious content), could restrict browser capabilities and mitigate
security problems posed by malicious data.

CSP works by emitting an HTTP header declaring the policy that browsers
should apply. Ideally, this header would be emitted by a layer above
Mercurial (likely the HTTP server doing the WSGI "proxying"). This
works for some CSP policies, but not all.

For example, policies to allow inline JavaScript may require setting
a "nonce" attribute on <script>. This attribute value must be unique
and non-guessable. And, the value must be present in the HTTP header
and the HTML body. This means that coordinating the value between
Mercurial and another HTTP server could be difficult: it is much
easier to generate and emit the nonce in a central location.

This commit introduces support for emitting a
Content-Security-Policy header from hgweb. A config option defines
the header value. If present, the header is emitted. A special
"%nonce%" syntax in the value triggers generation of a nonce and
inclusion in <script> elements in templates. The inclusion of a
nonce does not occur unless "%nonce%" is present. This makes this
commit completely backwards compatible and the feature opt-in.

The nonce is a type 4 UUID, which is the flavor that is randomly
generated. It has 122 random bits, which should be plenty to satisfy
the guarantees of a nonce.

-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----