1---
2c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
3SPDX-License-Identifier: curl
4Title: CURLOPT_SSL_OPTIONS
5Section: 3
6Source: libcurl
7See-also:
8  - CURLOPT_PROXY_SSL_OPTIONS (3)
9  - CURLOPT_SSLVERSION (3)
10  - CURLOPT_SSL_CIPHER_LIST (3)
11Protocol:
12  - TLS
13TLS-backend:
14  - All
15Added-in: 7.25.0
16---
17
18# NAME
19
20CURLOPT_SSL_OPTIONS - SSL behavior options
21
22# SYNOPSIS
23
24~~~c
25#include <curl/curl.h>
26
27CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSL_OPTIONS, long bitmask);
28~~~
29
30# DESCRIPTION
31
32Pass a long with a bitmask to tell libcurl about specific SSL
33behaviors. Available bits:
34
35## CURLSSLOPT_ALLOW_BEAST
36
37Tells libcurl to not attempt to use any workarounds for a security flaw in the
38SSL3 and TLS1.0 protocols. If this option is not used or this bit is set to 0,
39the SSL layer libcurl uses may use a work-around for this flaw although it
40might cause interoperability problems with some (older) SSL implementations.
41WARNING: avoiding this work-around lessens the security, and by setting this
42option to 1 you ask for exactly that. This option is only supported for Secure
43Transport and OpenSSL.
44
45## CURLSSLOPT_NO_REVOKE
46
47Tells libcurl to disable certificate revocation checks for those SSL backends
48where such behavior is present. This option is only supported for Schannel
49(the native Windows SSL library), with an exception in the case of Windows'
50Untrusted Publishers block list which it seems cannot be bypassed. (Added in
517.44.0)
52
53## CURLSSLOPT_NO_PARTIALCHAIN
54
55Tells libcurl to not accept "partial" certificate chains, which it otherwise
56does by default. This option is only supported for OpenSSL and fails the
57certificate verification if the chain ends with an intermediate certificate
58and not with a root cert. (Added in 7.68.0)
59
60## CURLSSLOPT_REVOKE_BEST_EFFORT
61
62Tells libcurl to ignore certificate revocation checks in case of missing or
63offline distribution points for those SSL backends where such behavior is
64present. This option is only supported for Schannel (the native Windows SSL
65library). If combined with *CURLSSLOPT_NO_REVOKE*, the latter takes
66precedence. (Added in 7.70.0)
67
68## CURLSSLOPT_NATIVE_CA
69
70Tell libcurl to use the operating system's native CA store for certificate
71verification. If you set this option and also set a CA certificate file or
72directory then during verification those certificates are searched in addition
73to the native CA store.
74
75Works with wolfSSL on Windows, Linux (Debian, Ubuntu, Gentoo, Fedora, RHEL),
76macOS, Android and iOS (added in 8.3.0), with GnuTLS (added in 8.5.0) or on
77Windows when built to use OpenSSL (Added in 7.71.0).
78
79## CURLSSLOPT_AUTO_CLIENT_CERT
80
81Tell libcurl to automatically locate and use a client certificate for
82authentication, when requested by the server. This option is only supported
83for Schannel (the native Windows SSL library). Prior to 7.77.0 this was the
84default behavior in libcurl with Schannel. Since the server can request any
85certificate that supports client authentication in the OS certificate store it
86could be a privacy violation and unexpected.
87(Added in 7.77.0)
88
89# DEFAULT
90
910
92
93# %PROTOCOLS%
94
95# EXAMPLE
96
97~~~c
98int main(void)
99{
100  CURL *curl = curl_easy_init();
101  if(curl) {
102    CURLcode res;
103    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/");
104    /* weaken TLS only for use with silly servers */
105    curl_easy_setopt(curl, CURLOPT_SSL_OPTIONS, (long)CURLSSLOPT_ALLOW_BEAST |
106                     CURLSSLOPT_NO_REVOKE);
107    res = curl_easy_perform(curl);
108    curl_easy_cleanup(curl);
109  }
110}
111~~~
112
113# %AVAILABILITY%
114
115# RETURN VALUE
116
117Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.
118