void gnutls_certificate_set_retrieve_function3(gnutls_certificate_credentials_t cred, gnutls_certificate_retrieve_function3 * func);
The callback's function prototype is defined in `abstract.h':
int gnutls_certificate_retrieve_function3( gnutls_session_t, const struct gnutls_cert_retr_st *info, gnutls_pcert_st **certs, unsigned int *certs_length, gnutls_ocsp_data_st **ocsp, unsigned int *ocsp_length, gnutls_privkey_t *privkey, unsigned int *flags);
The info field of the callback contains:
req_ca_dn which is a list with the CA names that the server considers trusted.
This is a hint and typically the client should send a certificate that is signed
by one of these CAs. These names, when available, are DER encoded. To get a more
meaningful value use the function gnutls_x509_rdn_get().
pk_algos contains a list with server's acceptable public key algorithms.
The certificate returned should support the server's given algorithms.
The callback should fill-in the following values:
certs should contain an allocated list of certificates and public keys.
certs_length is the size of the previous list.
ocsp should contain an allocated list of OCSP responses.
ocsp_length is the size of the previous list.
privkey is the private key.
If flags in the callback are set to GNUTLS_CERT_RETR_DEINIT_ALL then all provided values must be allocated using gnutls_malloc(), and will be released by gnutls; otherwise they will not be touched by gnutls.
The callback function should set the certificate and OCSP response list to be sent, and return 0 on success. If no certificates are available, the certs_length and ocsp_length should be set to zero. The return value (-1) indicates error and the handshake will be terminated. If both certificates are set in the credentials and a callback is available, the callback takes predence.
Raw public-keys:
In case raw public-keys are negotiated as certificate type, certificates
that would normally hold the public-key material are not available. In that case,
certs contains an allocated list with only the public key. Since there is no
certificate, there is also no certificate status. Therefore, OCSP information
should not be set.