Only use this in explicit fallback retries, following the guidance
in draft-ietf-tls-downgrade-scsv-00.
+=item SSL_MODE_ASYNC
+
+Enable asynchronous processing. TLS I/O operations may indicate a retry with
+SSL_ERROR_WANT_ASYNC with this mode set if an asynchronous capable engine is
+used to perform cryptographic operations. See L<SSL_get_error(3)>.
+
=back
=head1 RETURN VALUES
=head1 SEE ALSO
-L<ssl(3)>, L<SSL_read(3)>, L<SSL_write(3)>
+L<ssl(3)>, L<SSL_read(3)>, L<SSL_write(3)>, L<SSL_get_error(3)>
+
+=head1 HISTORY
+
+SSL_MODE_ASYNC was first added to OpenSSL 1.1.0.
+
+=head1 COPYRIGHT
+
+Copyright 2001-2016 The OpenSSL Project Authors. All Rights Reserved.
+
+Licensed under the OpenSSL license (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
+L<https://www.openssl.org/source/license.html>.
=cut