read_private_key
ret = read_private_key(fn, signer);
ret = read_private_key(opt->ca_private_key_string, &private_key);
ret = read_private_key(opt->certificate_private_key_string, &cert_key);
&& ctx->desc->read_private_key != NULL) {
key = ctx->desc->read_private_key(&p, bitlen, ispub);
b2i_of_void_fn *read_private_key;
&& ctx->desc->read_private_key != NULL) {
key = ctx->desc->read_private_key(in, ossl_pw_pvk_password, &pwdata,
b2i_PVK_of_bio_pw_fn *read_private_key;