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Code Issues Releases Wiki Activity
7ae59838f0
curl/docs/HSTS.md
Daniel Stenberg 7385610d0c
hsts: add support for Strict-Transport-Security 
- enable in the build (configure)
- header parsing
- host name lookup
- unit tests for the above
- CI build
- CURL_VERSION_HSTS bit
- curl_version_info support
- curl -V output
- curl-config --features
- CURLOPT_HSTS_CTRL
- man page for CURLOPT_HSTS_CTRL
- curl --hsts (sets CURLOPT_HSTS_CTRL and works with --libcurl)
- man page for --hsts
- save cache to disk
- load cache from disk
- CURLOPT_HSTS
- man page for CURLOPT_HSTS
- added docs/HSTS.md
- fixed --version docs
- adjusted curl_easy_duphandle

Closes #5896
2020-11-03 16:08:42 +01:00

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HSTS support

curl features EXPERIMENTAL support for the Strict-Transport-Security: HTTP header. Added in curl 7.74.0

Standard

HTTP Strict Transport Security

Behavior

libcurl features an in-memory cache for HSTS hosts, so that subsequent HTTP-only requests to a host name present in the cache will get internally "redirected" to the HTTPS version.

curl_easy_setopt() options:

  • CURLOPT_HSTS_CTRL - enable HSTS for this easy handle
  • CURLOPT_HSTS - specify file name where to store the HSTS cache on close (and possibly read from at startup)

curl cmdline options

  • --hsts [filename] - enable HSTS, use the file as HSTS cache. If filename is "" (no length) then no file will be used, only in-memory cache.

HSTS cache file format

Lines starting with # are ignored.

For each hsts entry:

[host name] "YYYYMMDD HH:MM:SS"

The [host name] is dot-prefixed if it is a includeSubDomain.

The time stamp is when the entry expires.

I considered using wget's file format for the HSTS cache. However, they store the time stamp as the epoch (number of seconds since 1970) and I strongly disagree with using that format. Instead I opted to use a format similar to the curl alt-svc cache file format.

Possible future additions

  • CURLOPT_HSTS_PRELOAD - provide a set of preloaded HSTS host names
  • ability to save to something else than a file