The problem is that the server failed to follow the rule that
every X509 object retrieved using SSL_get_peer_certificate()
must be explicitly freed by X509_free(). This caused a memory
leak for builds linked against OpenSSL where the X509 object
is reference counted -- improper counting will prevent the
object from being destroyed once the session containing the
peer certificate is freed.

The solution is to explicitly free every X509 object used.

mysql-test/r/openssl_1.result:
  Add test case result for Bug#42158
mysql-test/t/openssl_1.test:
  Add test case for Bug#42158
sql/sql_acl.cc:
  Deallocate X509 objects.