SSL_CTX_SET_CLIENT_CA_LIST(3) Library Functions Manual SSL_CTX_SET_CLIENT_CA_LIST(3)

SSL_CTX_set_client_CA_list, SSL_set_client_CA_list, SSL_CTX_add_client_CA, SSL_add_client_CA — set list of CAs sent to the client when requesting a client certificate

/* -lssl -lcrypto */
#include <openssl/ssl.h>

void
SSL_CTX_set_client_CA_list(SSL_CTX *ctx, STACK_OF(X509_NAME) *list);

void
SSL_set_client_CA_list(SSL *s, STACK_OF(X509_NAME) *list);

int
SSL_CTX_add_client_CA(SSL_CTX *ctx, X509 *cacert);

int
SSL_add_client_CA(SSL *ssl, X509 *cacert);

() sets the list of CAs sent to the client when requesting a client certificate for ctx.

() sets the list of CAs sent to the client when requesting a client certificate for the chosen ssl, overriding the setting valid for ssl's SSL_CTX object.

() adds the CA name extracted from cacert to the list of CAs sent to the client when requesting a client certificate for ctx.

() adds the CA name extracted from cacert to the list of CAs sent to the client when requesting a client certificate for the chosen ssl, overriding the setting valid for ssl's SSL_CTX object.

When a TLS/SSL server requests a client certificate (see ()), it sends a list of CAs for which it will accept certificates to the client.

This list must explicitly be set using () for ctx and SSL_set_client_CA_list() for the specific ssl. The list specified overrides the previous setting. The CAs listed do not become trusted (list only contains the names, not the complete certificates); use SSL_CTX_load_verify_locations(3) to additionally load them for verification.

If the list of acceptable CAs is compiled in a file, the SSL_load_client_CA_file(3) function can be used to help importing the necessary data.

() and SSL_add_client_CA() can be used to add additional items the list of client CAs. If no list was specified before using SSL_CTX_set_client_CA_list() or SSL_set_client_CA_list(), a new client CA list for ctx or ssl (as appropriate) is opened.

These functions are only useful for TLS/SSL servers.

SSL_CTX_add_client_CA() and SSL_add_client_CA() have the following return values:

0
A failure while manipulating the STACK_OF(X509_NAME) object occurred or the X509_NAME could not be extracted from cacert. Check the error stack to find out the reason.
1
The operation succeeded.

Scan all certificates in CAfile and list them as acceptable CAs:

SSL_CTX_set_client_CA_list(ctx, SSL_load_client_CA_file(CAfile));

ssl(3), SSL_CTX_load_verify_locations(3), SSL_get_client_CA_list(3), SSL_load_client_CA_file(3), X509_NAME_new(3)

SSL_CTX_set_client_CA_list(), SSL_set_client_CA_list(), SSL_CTX_add_client_CA(), and SSL_add_client_CA() first appeared in SSLeay 0.8.0 and have been available since OpenBSD 2.4.

OpenBSD 7.8 June 8, 2025 SSL_CTX_SET_CLIENT_CA_LIST(3)