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45 lines
1.4 KiB
Markdown
45 lines
1.4 KiB
Markdown
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# HSTS support
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curl features **EXPERIMENTAL** support for the Strict-Transport-Security: HTTP
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header. Added in curl 7.74.0
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## Standard
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[HTTP Strict Transport Security](https://tools.ietf.org/html/rfc6797)
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## Behavior
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libcurl features an in-memory cache for HSTS hosts, so that subsequent
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HTTP-only requests to a host name present in the cache will get internally
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"redirected" to the HTTPS version.
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## `curl_easy_setopt()` options:
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- `CURLOPT_HSTS_CTRL` - enable HSTS for this easy handle
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- `CURLOPT_HSTS` - specify file name where to store the HSTS cache on close
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(and possibly read from at startup)
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## curl cmdline options
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- `--hsts [filename]` - enable HSTS, use the file as HSTS cache. If filename
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is `""` (no length) then no file will be used, only in-memory cache.
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## HSTS cache file format
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Lines starting with `#` are ignored.
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For each hsts entry:
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[host name] "YYYYMMDD HH:MM:SS"
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The `[host name]` is dot-prefixed if it is a includeSubDomain.
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The time stamp is when the entry expires.
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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.
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## Possible future additions
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- `CURLOPT_HSTS_PRELOAD` - provide a set of preloaded HSTS host names
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- ability to save to something else than a file
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