Ubuntu Manpage: CURLOPT_SSL_OPTIONS

Provided by: libcurl4-doc_8.14.1-2ubuntu1_all

NAME

       CURLOPT_SSL_OPTIONS - SSL behavior options

SYNOPSIS

       #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. This
option is independent of other CA certificate locations set at run time or build time. Those
locations 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) and with OpenSSL and its forks (LibreSSL,
BoringSSL, etc) on Windows (Added in 7.71.0).

This works with rustls on Windows, macOS, Android and iOS. On Linux it is equivalent to using the
Mozilla CA certificate bundle. When used with rustls _only_ the native CA store is consulted, not
other locations set at run time or build time. (Added in 8.13.0)

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)

CURLSSLOPT_EARLYDATA
Tell libcurl to try sending application data as TLS1.3 early data. This option is supported for
GnuTLS, wolfSSL, quictls and OpenSSL (but not BoringSSL or AWS-LC). It works on TCP and QUIC
connections using ngtcp2. This option works on a best effort basis, in cases when it wasn't
possible to send early data the request is resent normally post-handshake. This option does not
work when using QUIC. (Added in 8.11.0 for GnuTLS and 8.13.0 for wolfSSL, quictls and OpenSSL)

DEFAULT

PROTOCOLS

       This functionality affects all TLS based protocols: HTTPS, FTPS, IMAPS, POP3S, SMTPS etc.

       All TLS backends support this option.

EXAMPLE

       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 curl 7.25.0

RETURN VALUE

       curl_easy_setopt(3) returns a CURLcode indicating success or error.

       CURLE_OK (0) means everything was OK, non-zero means an error occurred, see libcurl-errors(3).