OPENSSL_Applink - glue between OpenSSL BIO and Win32 compiler run-time
 __declspec(dllexport) void **OPENSSL_Applink();
OPENSSL_Applink is application-side interface which provides a glue between
  OpenSSL BIO layer and Win32 compiler run-time environment. Even though it
  appears at application side, it's essentially OpenSSL private interface. For
  this reason application developers are not expected to implement it, but to
  compile provided module with compiler of their choice and link it into the
  target application. The referred module is available as applink.c,
  located alongside the public header files (only on the platforms where
  applicable).
Copyright 2004-2018 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the Apache License 2.0 (the "License").
    You may not use this file except in compliance with the License. You can
    obtain a copy in the file LICENSE in the source distribution or at
    <https://www.openssl.org/source/license.html>.