Goncalo Gomes authored Sep 01, 2022 and Marge Bot committed Sep 12, 2022

There are too many similarities between GnuTLS session ID and the
session cache, so it is desirable to merge the implementations so
that it is easier to maintain and leads to more similar behaviours
across backends.

This commit moves the OpenSSL backend session cache implementation
to the base class as well as the session id calculation.

In GnuTLS the session id is also used to assert that the copy session
state is done properly (before handshake of the new class and after
handshake of the old class). That behaviour was maintained but the
session id is now computed when the base class is constructed.

Adds as well some operations that need to be abstracted in order for
the lifetime of the different objects in each backend to be
maintained properly.

Fixes #194

Part-of: <!221>