User-agent information is used to try to detect the user OS; since the
UA is extracted for QUIC traffic too, the "detected_os" field must be
generic and not associated to HTTP flows only.
Otherwise, you might overwrite some "tls_quic_stun" fields (SNI...) with
random data.
Strangely enough, the "detected_os" field is never used: it is never
logged, or printed, or exported...
In a Client Hello, the presence of both SNI and ESNI may obfuscate the real
domain of an HTTPS connection, fooling DPI engines and firewalls, similarly
to Domain Fronting.
Such technique is reported in a presentation at DEF CON 28:
"Domain Fronting is Dead, Long Live Domain Fronting: Using TLS 1.3 to evade
censors, bypass network defenses, and blend in with the noise"
Full credit for the idea must go the original author
At the moment, the only way to get the pdf presention and related video is via
https://forum.defcon.org/node/234492
Hopefully a direct link (and an example pcap) will be available soon
