c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
SPDX-License-Identifier: curl
Long: hsts
Arg: <file name>
Protocols: HTTPS
Help: Enable HSTS with this cache file
Added: 7.74.0
Category: http
Example: --hsts cache.txt $URL
See-also: proto
Multi: append
---
This option enables HSTS for the transfer. If the file name points to an
existing HSTS cache file, that is used. After a completed transfer, the
cache is saved to the file name again if it has been modified.

If curl is told to use HTTP:// for a transfer involving a host name that
exists in the HSTS cache, it upgrades the transfer to use HTTPS. Each HSTS
cache entry has an individual life time after which the upgrade is no longer
performed.

Specify a "" file name (zero length) to avoid loading/saving and make curl
just handle HSTS in memory.

If this option is used several times, curl loads contents from all the
files but the last one is used for saving.
