SSL_get_peer_certificate.3ssl man page
SSL_get_peer_certificate — get the X509 certificate of the peer
#include <openssl/ssl.h> X509 *SSL_get_peer_certificate(const SSL *ssl);
SSL_get_peer_certificate() returns a pointer to the X509 certificate the peer presented. If the peer did not present a certificate, NULL is returned.
Due to the protocol definition, a TLS/SSL server will always send a certificate, if present. A client will only send a certificate when explicitly requested to do so by the server (see SSL_CTX_set_verify(3)). If an anonymous cipher is used, no certificates are sent.
That a certificate is returned does not indicate information about the verification state, use SSL_get_verify_result(3) to check the verification state.
The reference count of the X509 object is incremented by one, so that it will not be destroyed when the session containing the peer certificate is freed. The X509 object must be explicitly freed using X509_free().
The following return values can occur:
No certificate was presented by the peer or no connection was established.
- Pointer to an X509 certificate
The return value points to the certificate presented by the peer.
ssl(3), SSL_get_verify_result(3), SSL_CTX_set_verify(3)