Some Linux distros have begun disabling TLSv1.0 and TLSv1.1 by default
for security reasons, for example in Fedora 33 onwards:
https://fedoraproject.org/wiki/Changes/StrongCryptoSettings2
Use TLSv1.2 for the fake TLS servers created in the test suite, to avoid
failures due to OpenSSL disallowing TLSv1.0:
<twisted.python.failure.Failure OpenSSL.SSL.Error: [('SSL routines',
'ssl_choose_client_version', 'unsupported protocol')]>
Signed-off-by: Dan Callaghan <djc@djc.id.au>
The `http_proxy` and `HTTPS_PROXY` env vars can be set to a `host[:port]` value which should point to a proxy.
The address of the proxy should be excluded from IP blacklists such as the `url_preview_ip_range_blacklist`.
The proxy will then be used for
* push
* url previews
* phone-home stats
* recaptcha validation
* CAS auth validation
It will *not* be used for:
* Application Services
* Identity servers
* Outbound federation
* In worker configurations, connections from workers to masters
Fixes#4198.
Make sure that server_names used in auth headers are sane, and reject them with
a sensible error code, before they disappear off into the depths of the system.
