is a file that containing the certificate list (path) for
the specified private key, in PKCS7 format, or a list of certificates
const char * keyfile
is a file that contains the private key
gnutls_x509_crt_fmt_t type
is PEM or DER
DESCRIPTION
This function sets a certificate/private key pair in the
gnutls_certificate_credentials_t structure. This function may be
called more than once (in case multiple keys/certificates exist
for the server).
Currently only PKCS-1 encoded RSA and DSA private keys are accepted by
this function.