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
The Lufthansa in-flight wifi generates a synthetic 204 response to the DERP server's /generate_204 endpoint. This PR adds a basic challenge/response to the endpoint; something sufficiently complicated that it's unlikely to be implemented by a captive portal. We can then check for the expected response to verify whether we're being MITM'd. Follow-up to #5601 Signed-off-by: Andrew Dunham <andrew@du.nham.ca> Change-Id: I94a68c9a16a7be7290200eea6a549b64f02ff48f