curl/docs/libcurl/opts/CURLOPT_SSL_OPTIONS.md
Daniel Stenberg eefcc1bda4
docs: introduce "curldown" for libcurl man page format
curldown is this new file format for libcurl man pages. It is markdown
inspired with differences:

- Each file has a set of leading headers with meta-data
- Supports a small subset of markdown
- Uses .md file extensions for editors/IDE/GitHub to treat them nicely
- Generates man pages very similar to the previous ones
- Generates man pages that still convert nicely to HTML on the website
- Detects and highlights mentions of curl symbols automatically (when
  their man page section is specified)

tools:

- cd2nroff: converts from curldown to nroff man page
- nroff2cd: convert an (old) nroff man page to curldown
- cdall: convert many nroff pages to curldown versions
- cd2cd: verifies and updates a curldown to latest curldown

This setup generates .3 versions of all the curldown versions at build time.

CI:

Since the documentation is now technically markdown in the eyes of many
things, the CI runs many more tests and checks on this documentation,
including proselint, link checkers and tests that make sure we capitalize the
first letter after a period...

Closes #12730
2024-01-23 00:29:02 +01:00

117 lines
3.5 KiB
Markdown

---
c: Copyright (C) Daniel Stenberg, <daniel.se>, et al.
SPDX-License-Identifier: curl
Title: CURLOPT_SSL_OPTIONS
Section: 3
Source: libcurl
See-also:
- CURLOPT_PROXY_SSL_OPTIONS (3)
- CURLOPT_SSLVERSION (3)
- CURLOPT_SSL_CIPHER_LIST (3)
---
# NAME
CURLOPT_SSL_OPTIONS - SSL behavior options
# SYNOPSIS
~~~c
#include <curl/curl.h>
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSL_OPTIONS, long bitmask);
~~~
# DESCRIPTION
Pass a long with a bitmask to tell libcurl about specific SSL
behaviors. Available bits:
## CURLSSLOPT_ALLOW_BEAST
Tells libcurl to not attempt to use any workarounds for a security flaw in the
SSL3 and TLS1.0 protocols. If this option is not used or this bit is set to 0,
the SSL layer libcurl uses may use a work-around for this flaw although it
might cause interoperability problems with some (older) SSL implementations.
WARNING: avoiding this work-around lessens the security, and by setting this
option to 1 you ask for exactly that. This option is only supported for Secure
Transport and OpenSSL.
## CURLSSLOPT_NO_REVOKE
Tells libcurl to disable certificate revocation checks for those SSL backends
where such behavior is present. This option is only supported for Schannel
(the native Windows SSL library), with an exception in the case of Windows'
Untrusted Publishers block list which it seems cannot be bypassed. (Added in
7.44.0)
## CURLSSLOPT_NO_PARTIALCHAIN
Tells libcurl to not accept "partial" certificate chains, which it otherwise
does by default. This option is only supported for OpenSSL and fails the
certificate verification if the chain ends with an intermediate certificate
and not with a root cert. (Added in 7.68.0)
## CURLSSLOPT_REVOKE_BEST_EFFORT
Tells libcurl to ignore certificate revocation checks in case of missing or
offline distribution points for those SSL backends where such behavior is
present. This option is only supported for Schannel (the native Windows SSL
library). If combined with *CURLSSLOPT_NO_REVOKE*, the latter takes
precedence. (Added in 7.70.0)
## CURLSSLOPT_NATIVE_CA
Tell libcurl to use the operating system's native CA store for certificate
verification. If you set this option and also set a CA certificate file or
directory then during verification those certificates are searched in addition
to the native CA store.
Works with wolfSSL on Windows, Linux (Debian, Ubuntu, Gentoo, Fedora, RHEL),
macOS, Android and iOS (added in 8.3.0), with GnuTLS (added in 8.5.0) or on
Windows when built to use OpenSSL (Added in 7.71.0).
## CURLSSLOPT_AUTO_CLIENT_CERT
Tell libcurl to automatically locate and use a client certificate for
authentication, when requested by the server. This option is only supported
for Schannel (the native Windows SSL library). Prior to 7.77.0 this was the
default behavior in libcurl with Schannel. Since the server can request any
certificate that supports client authentication in the OS certificate store it
could be a privacy violation and unexpected.
(Added in 7.77.0)
# DEFAULT
0
# PROTOCOLS
All TLS-based protocols
# EXAMPLE
~~~c
int main(void)
{
CURL *curl = curl_easy_init();
if(curl) {
CURLcode res;
curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/");
/* weaken TLS only for use with silly servers */
curl_easy_setopt(curl, CURLOPT_SSL_OPTIONS, (long)CURLSSLOPT_ALLOW_BEAST |
CURLSSLOPT_NO_REVOKE);
res = curl_easy_perform(curl);
curl_easy_cleanup(curl);
}
}
~~~
# AVAILABILITY
Added in 7.25.0
# RETURN VALUE
Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.