int tls_construct_certificate_request(SSL *s)
{
    unsigned char *p, *d;
    int i, j, nl, off, n;
    STACK_OF(X509_NAME) *sk = NULL;
    X509_NAME *name;
    BUF_MEM *buf;

    buf = s->init_buf;

    d = p = ssl_handshake_start(s);

    /* get the list of acceptable cert types */
    p++;
    n = ssl3_get_req_cert_type(s, p);
    d[0] = n;
    p += n;
    n++;

    if (SSL_USE_SIGALGS(s)) {
        const unsigned char *psigs;
        unsigned char *etmp = p;
        nl = tls12_get_psigalgs(s, &psigs);
        /* Skip over length for now */
        p += 2;
        nl = tls12_copy_sigalgs(s, p, psigs, nl);
        /* Now fill in length */
        s2n(nl, etmp);
        p += nl;
        n += nl + 2;
    }

    off = n;
    p += 2;
    n += 2;

    sk = SSL_get_client_CA_list(s);
    nl = 0;
    if (sk != NULL) {
        for (i = 0; i < sk_X509_NAME_num(sk); i++) {
            name = sk_X509_NAME_value(sk, i);
            j = i2d_X509_NAME(name, NULL);
            if (!BUF_MEM_grow_clean
                (buf, SSL_HM_HEADER_LENGTH(s) + n + j + 2)) {
                SSLerr(SSL_F_TLS_CONSTRUCT_CERTIFICATE_REQUEST,
                       ERR_R_BUF_LIB);
                goto err;
            }
            p = ssl_handshake_start(s) + n;
            s2n(j, p);
            i2d_X509_NAME(name, &p);
            n += 2 + j;
            nl += 2 + j;
        }
    }
    /* else no CA names */
    p = ssl_handshake_start(s) + off;
    s2n(nl, p);

    if (!ssl_set_handshake_header(s, SSL3_MT_CERTIFICATE_REQUEST, n)) {
        SSLerr(SSL_F_TLS_CONSTRUCT_CERTIFICATE_REQUEST, ERR_R_INTERNAL_ERROR);
        goto err;
    }

    s->s3->tmp.cert_request = 1;

    return 1;
 err:
    ossl_statem_set_error(s);
    return 0;
}