/usr/man/cat.3/SSL_set_cert_cb.3.Z

NAME

       SSL_CTX_set_cert_cb, SSL_set_cert_cb - handle certificate callback
       function

SYNOPSIS

        #include <openssl/ssl.h>

        void SSL_CTX_set_cert_cb(SSL_CTX *c, int (*cert_cb)(SSL *ssl, void *arg), void *arg);
        void SSL_set_cert_cb(SSL *s, int (*cert_cb)(SSL *ssl, void *arg), void *arg);

        int (*cert_cb)(SSL *ssl, void *arg);

DESCRIPTION

       SSL_CTX_set_cert_cb() and SSL_set_cert_cb() sets the cceerrtt_ccbb(()) call-
       back, arg value is pointer which is passed to the application callback.

       When cceerrtt_ccbb(()) is NULL, no callback function is used.

       cert_cb() is the application defined callback. It is called before a
       certificate will be used by a client or server. The callback can then
       inspect the passed ssl structure and set or clear any appropriate cer-
       tificates. If the callback is successful it MUST return 1 even if no
       certificates have been set. A zero is returned on error which will
       abort the handshake with a fatal internal error alert. A negative
       return value will suspend the handshake and the handshake function will
       return immediately.  SSL_get_error(3) will return
       SSL_ERROR_WANT_X509_LOOKUP to indicate, that the handshake was sus-
       pended. The next call to the handshake function will again lead to the
       call of cert_cb(). It is the job of the cert_cb() to store information
       about the state of the last call, if required to continue.

       An application will typically call SSL_use_certificate() and
       SSL_use_PrivateKey() to set the end entity certificate and private key.
       It can add intermediate and optionally the root CA certificates using
       SSL_add1_chain_cert().

       It might also call SSL_certs_clear() to delete any certificates associ-
       ated with the SSL object.

       The certificate callback functionality supercedes the (largely broken)
       functionality provided by the old client certificate callback inter-
       face.  It is always called even is a certificate is already set so the
       callback can modify or delete the existing certificate.

       A more advanced callback might examine the handshake parameters and set
       whatever chain is appropriate. For example a legacy client supporting
       only TLS v1.0 might receive a certificate chain signed using SHA1
       whereas a TLS v1.2 client which advertises support for SHA256 could
       receive a chain using SHA256.

       Normal server sanity checks are performed on any certificates set by
       the callback. So if an EC chain is set for a curve the client does not
       support it will not be used.

       ssl(3), SSL_use_certificate(3), SSL_add1_chain_cert(3),
       SSL_get_client_CA_list(3), SSL_clear(3), SSL_free(3)

1.0.2t                            2019-09-10            SSL_CTX_set_cert_cb(3)
See also SSL_CTX_set_cert_cb(3)