LIBRESSL-SSL_CTX_SET_CLIENT_CA_LIST(3)

💅 SSL_CTX_SET_CLIENT_CA_LIST(3) — the set-client-CA-list bestie era ✨

okay so this is one of those libssl / libcrypto man pages (manual name: SSL_CTX_SET_CLIENT_CA_LI(3), yes the title got cut off, we don't talk about it 💀) and it's all about the list of CAs a server sends to a client when it's like "hey babe, show me your certificate".

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🌸 NAME 🌸

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

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🎀 SYNOPSIS 🎀

library “libssl” libcrypto
#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);

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🦋 DESCRIPTION 🦋

so here's the tea, fr fr 🍵

• SSL_CTX_set_client_CA_list() sets the list of CAs sent to the client when requesting a client certificate for ctx. like, the whole context's vibe check list 💅
• SSL_set_client_CA_list() 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. main character energy — it does NOT care what the context said ✨
• SSL_CTX_add_client_CA() adds the CA name extracted from cacert to the list of CAs sent to the client when requesting a client certificate for ctx 🎀
• SSL_add_client_CA() 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 SSL_CTX_set_verify()), it sends a list of CAs for which it will accept certificates to the client. iykyk 🌈

👑 not me reminding you: this list must explicitly be set using SSL_CTX_set_client_CA_list() for ctx and SSL_set_client_CA_list() for the specific ssl. the list specified overrides the previous setting. and the CAs listed do not become trusted (the list only contains the names, not the complete certificates) — use SSL_CTX_load_verify_locations(3) to additionally load them for verification. no cap, that part matters 😭

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. obsessed with a convenience function 🫶

SSL_CTX_add_client_CA() and SSL_add_client_CA() can be used to add additional items to 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 💜

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⭐ RETURN VALUES ⭐

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 🎉

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🔥 EXAMPLES 🔥

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

SSL_CTX_set_client_CA_list(ctx, SSL_load_client_CA_file(CAfile));

one line, ate, periodt 💅

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🌈 SEE ALSO 🌈

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

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💖 HISTORY 💖

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 👑

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okay that's the whole page bestie, go set your CA lists 💜 — this icon was brought to you by Debian, dated June 8, 2025, answering to the name SSL_CTX_SET_CLIENT_CA_LIST(3) 🎀✨