Adds the experimental feature `ssls-export` to libcurl and curl for
importing and exporting SSL sessions from/to a file.
* add functions to libcurl API
* add command line option `--ssl-sessions <filename>` to curl
* add documenation
* add support in configure
* add support in cmake
+ add pytest case
Closes#15924
When a QUIC TLS session announced early data support and
'CURLSSLOPT_EARLYDATA' is set for the transfer, send initial request and
body (up to the 128k we buffer) as 0RTT when curl is built with
ngtcp2+gnutls.
QUIC 0RTT needs not only the TLS session but the QUIC transport
paramters as well. Store those and the earlydata max value together with
the session in the cache.
Add test case for h3 use of this. Enable quic early data in nghttpx for
testing.
Closes#15667
Described in detail in internal doc TLS-SESSIONS.md
Main points:
- use a new `ssl_peer_key` for cache lookups by connection filters
- recognize differences between TLSv1.3 and other tickets
* TLSv1.3 tickets are single-use, cache can hold several of them for a peer
* TLSv1.2 are reused, keep only a single one per peer
- differentiate between ticket BLOB to store (that could be persisted) and object instances
- use put/take/return pattern for cache access
- remember TLS version, ALPN protocol, time received and lifetime of ticket
- auto-expire tickets after their lifetime
Closes#15774
