1. Add a new verification callback. This gives an option
to report errors directly from this callback (by emitting
handshakeInterruptedOnError()). This allows an application
to explain to its peer why the handshake was interrupted (by
sending a corresponding alert message).
2. This also means we want to notice such alerts (in Qt,
from the application's point of view, they are mostly
informational only, no interaction is required). So we
also introduce a new 'info callback', that can notice alert
messages read or written. We also introduce two new enums
describing the level and type of an alert message. QSslSocket
gets three new signals (for incoming/outgoing alerts and
verification errors found early).
3. In case we requested a certificate, but the peer provided
none, we would previously abruptly close the connection without
a proper alert message (and such a situation is not handled
by any verification callbacks, since there is no certificate(s)
to verify essentially). So we now introduce a new verification
option that maps to what OpenSSL calls 'SSL_VERIFY_FAIL_IF_NO_PEER_CERT'.
This way, the proper alert will be generated.
Fixes: QTBUG-68419
Change-Id: I5d1e9298b4040a2d4f867f5b1a3567a2253927b8
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
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