Bugfix
   * Fixed a regression introduced in 3.6.0 where the CA callback set with
     mbedtls_ssl_conf_ca_cb() would stop working when connections were
     upgraded to TLS 1.3. Fixed by adding support for the CA callback with TLS
     1.3.
   * Fixed a regression introduced in 3.6.0 where clients that relied on
     optional/none authentication mode, by calling mbedtls_ssl_conf_authmode()
     with MBEDTLS_SSL_VERIFY_OPTIONAL or MBEDTLS_SSL_VERIFY_NONE, would stop
     working when connections were upgraded to TLS 1.3. Fixed by adding
     support for optional/none with TLS 1.3 as well. Note that the TLS 1.3
     standard makes server authentication mandatory; users are advised not to
     use authmode none, and to carefully check the results when using optional
     mode.
   * Fixed a regression introduced in 3.6.0 where context-specific certificate
     verify callbacks, set with mbedtls_ssl_set_verify() as opposed to
     mbedtls_ssl_conf_verify(), would stop working when connections were
     upgraded to TLS 1.3. Fixed by adding support for context-specific verify
     callback in TLS 1.3.