/*
 * Copyright (C) 2001, 2002, 2003, 2004, 2005, 2006, 2007 Free Software Foundation
 *
 * Author: Nikos Mavrogiannopoulos
 *
 * This file is part of GNUTLS.
 *
 * The GNUTLS library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public License
 * as published by the Free Software Foundation; either version 2.1 of
 * the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
 * USA
 *
 */

/* Some of the stuff needed for Certificate authentication is contained
 * in this file.
 */

#include <gnutls_int.h>
#include <gnutls_errors.h>
#include <auth_cert.h>
#include <gnutls_cert.h>
#include <libtasn1.h>
#include <gnutls_datum.h>
#include <gnutls_mpi.h>
#include <gnutls_global.h>
#include <gnutls_algorithms.h>
#include <gnutls_dh.h>
#include <gnutls_str.h>
#include <gnutls_state.h>
#include <gnutls_auth_int.h>
#include <gnutls_x509.h>
/* x509 */
#include "x509.h"
#include "mpi.h"

/**
  * MHD__gnutls_certificate_free_keys - Used to free all the keys from a MHD_gtls_cert_credentials_t structure
  * @sc: is an #MHD_gtls_cert_credentials_t structure.
  *
  * This function will delete all the keys and the certificates associated
  * with the given credentials. This function must not be called when a
  * TLS negotiation that uses the credentials is in progress.
  *
  **/
void
MHD__gnutls_certificate_free_keys (MHD_gtls_cert_credentials_t sc)
{
  unsigned i, j;

  for (i = 0; i < sc->ncerts; i++)
    {
      for (j = 0; j < sc->cert_list_length[i]; j++)
        {
          MHD_gtls_gcert_deinit (&sc->cert_list[i][j]);
        }
      MHD_gnutls_free (sc->cert_list[i]);
    }

  MHD_gnutls_free (sc->cert_list_length);
  sc->cert_list_length = NULL;

  MHD_gnutls_free (sc->cert_list);
  sc->cert_list = NULL;

  for (i = 0; i < sc->ncerts; i++)
    {
      MHD_gtls_gkey_deinit (&sc->pkey[i]);
    }

  MHD_gnutls_free (sc->pkey);
  sc->pkey = NULL;

  sc->ncerts = 0;

}

/**
  * MHD__gnutls_certificate_free_cas - Used to free all the CAs from a MHD_gtls_cert_credentials_t structure
  * @sc: is an #MHD_gtls_cert_credentials_t structure.
  *
  * This function will delete all the CAs associated
  * with the given credentials. Servers that do not use
  * MHD_gtls_certificate_verify_peers2() may call this to
  * save some memory.
  *
  **/
void
MHD__gnutls_certificate_free_cas (MHD_gtls_cert_credentials_t sc)
{
  unsigned j;

  for (j = 0; j < sc->x509_ncas; j++)
    {
      MHD_gnutls_x509_crt_deinit (sc->x509_ca_list[j]);
    }

  sc->x509_ncas = 0;

  MHD_gnutls_free (sc->x509_ca_list);
  sc->x509_ca_list = NULL;

}

/**
  * MHD__gnutls_certificate_free_ca_names - Used to free all the CA names from a MHD_gtls_cert_credentials_t structure
  * @sc: is an #MHD_gtls_cert_credentials_t structure.
  *
  * This function will delete all the CA name in the
  * given credentials. Clients may call this to save some memory
  * since in client side the CA names are not used.
  *
  * CA names are used by servers to advertize the CAs they
  * support to clients.
  *
  **/
void
MHD__gnutls_certificate_free_ca_names (MHD_gtls_cert_credentials_t sc)
{
  MHD__gnutls_free_datum (&sc->x509_rdn_sequence);
}

/*-
  * MHD_gtls_certificate_get_rsa_params - Returns the RSA parameters pointer
  * @rsa_params: holds the RSA parameters or NULL.
  * @func: function to retrieve the parameters or NULL.
  * @session: The session.
  *
  * This function will return the rsa parameters pointer.
  *
  -*/
MHD_gtls_rsa_params_t
MHD_gtls_certificate_get_rsa_params (MHD_gtls_rsa_params_t rsa_params,
                                     MHD_gnutls_params_function * func,
                                     MHD_gtls_session_t session)
{
  MHD_gnutls_params_st params;
  int ret;

  if (session->internals.params.rsa_params)
    {
      return session->internals.params.rsa_params;
    }

  if (rsa_params)
    {
      session->internals.params.rsa_params = rsa_params;
    }
  else if (func)
    {
      ret = func (session, GNUTLS_PARAMS_RSA_EXPORT, &params);
      if (ret == 0 && params.type == GNUTLS_PARAMS_RSA_EXPORT)
        {
          session->internals.params.rsa_params = params.params.rsa_export;
          session->internals.params.free_rsa_params = params.deinit;
        }
    }

  return session->internals.params.rsa_params;
}


/**
  * MHD__gnutls_certificate_free_credentials - Used to free an allocated MHD_gtls_cert_credentials_t structure
  * @sc: is an #MHD_gtls_cert_credentials_t structure.
  *
  * This structure is complex enough to manipulate directly thus
  * this helper function is provided in order to free (deallocate) it.
  *
  * This function does not free any temporary parameters associated
  * with this structure (ie RSA and DH parameters are not freed by
  * this function).
  **/
void
MHD__gnutls_certificate_free_credentials (MHD_gtls_cert_credentials_t sc)
{
  MHD__gnutls_certificate_free_keys (sc);
  MHD__gnutls_certificate_free_cas (sc);
  MHD__gnutls_certificate_free_ca_names (sc);
#ifdef ENABLE_PKI
  MHD__gnutls_certificate_free_crls (sc);
#endif

#ifdef KEYRING_HACK
  MHD__gnutls_free_datum (&sc->keyring);
#endif

  MHD_gnutls_free (sc);
}


/**
  * MHD__gnutls_certificate_allocate_credentials - Used to allocate a MHD_gtls_cert_credentials_t structure
  * @res: is a pointer to an #MHD_gtls_cert_credentials_t structure.
  *
  * This structure is complex enough to manipulate directly thus this
  * helper function is provided in order to allocate it.
  *
  * Returns: %GNUTLS_E_SUCCESS on success, or an error code.
  **/
int
MHD__gnutls_certificate_allocate_credentials (MHD_gtls_cert_credentials_t *
                                              res)
{
  *res = MHD_gnutls_calloc (1, sizeof (MHD_gtls_cert_credentials_st));

  if (*res == NULL)
    return GNUTLS_E_MEMORY_ERROR;

  (*res)->verify_bits = DEFAULT_VERIFY_BITS;
  (*res)->verify_depth = DEFAULT_VERIFY_DEPTH;

  return 0;
}


/* returns the KX algorithms that are supported by a
 * certificate. (Eg a certificate with RSA params, supports
 * GNUTLS_KX_RSA algorithm).
 * This function also uses the KeyUsage field of the certificate
 * extensions in order to disable unneded algorithms.
 */
int
MHD_gtls_selected_cert_supported_kx (MHD_gtls_session_t session,
                                     enum MHD_GNUTLS_KeyExchangeAlgorithm
                                     **alg, int *alg_size)
{
  enum MHD_GNUTLS_KeyExchangeAlgorithm kx;
  enum MHD_GNUTLS_PublicKeyAlgorithm pk;
  enum MHD_GNUTLS_KeyExchangeAlgorithm kxlist[MAX_ALGOS];
  MHD_gnutls_cert *cert;
  int i;

  if (session->internals.selected_cert_list_length == 0)
    {
      *alg_size = 0;
      *alg = NULL;
      return 0;
    }

  cert = &session->internals.selected_cert_list[0];
  i = 0;

  for (kx = 0; kx < MAX_ALGOS; kx++)
    {
      pk = MHD_gtls_map_pk_get_pk (kx);
      if (pk == cert->subject_pk_algorithm)
        {
          /* then check key usage */
          if (MHD__gnutls_check_key_usage (cert, kx) == 0)
            {
              kxlist[i] = kx;
              i++;
            }
        }
    }

  if (i == 0)
    {
      MHD_gnutls_assert ();
      return GNUTLS_E_INVALID_REQUEST;
    }

  *alg =
    MHD_gnutls_calloc (1, sizeof (enum MHD_GNUTLS_KeyExchangeAlgorithm) * i);
  if (*alg == NULL)
    return GNUTLS_E_MEMORY_ERROR;

  *alg_size = i;

  memcpy (*alg, kxlist, i * sizeof (enum MHD_GNUTLS_KeyExchangeAlgorithm));

  return 0;
}


/**
  * MHD_gtls_certificate_server_set_request - Used to set whether to request a client certificate
  * @session: is an #MHD_gtls_session_t structure.
  * @req: is one of GNUTLS_CERT_REQUEST, GNUTLS_CERT_REQUIRE
  *
  * This function specifies if we (in case of a server) are going
  * to send a certificate request message to the client. If @req
  * is GNUTLS_CERT_REQUIRE then the server will return an error if
  * the peer does not provide a certificate. If you do not
  * call this function then the client will not be asked to
  * send a certificate.
  **/
void
MHD_gtls_certificate_server_set_request (MHD_gtls_session_t session,
                                         MHD_gnutls_certificate_request_t req)
{
  session->internals.send_cert_req = req;
}

/**
  * MHD_gtls_certificate_client_set_retrieve_function - Used to set a callback to retrieve the certificate
  * @cred: is a #MHD_gtls_cert_credentials_t structure.
  * @func: is the callback function
  *
  * This function sets a callback to be called in order to retrieve the certificate
  * to be used in the handshake.
  * The callback's function prototype is:
  * int (*callback)(MHD_gtls_session_t, const MHD_gnutls_datum_t* req_ca_dn, int nreqs,
  * const enum MHD_GNUTLS_PublicKeyAlgorithm* pk_algos, int pk_algos_length, MHD_gnutls_retr_st* st);
  *
  * @req_ca_cert is only used in X.509 certificates.
  * Contains a list with the CA names that the server considers trusted.
  * Normally we should send a certificate that is signed
  * by one of these CAs. These names are DER encoded. To get a more
  * meaningful value use the function MHD_gnutls_x509_rdn_get().
  *
  * @pk_algos contains a list with server's acceptable signature algorithms.
  * The certificate returned should support the server's given algorithms.
  *
  * @st should contain the certificates and private keys.
  *
  * If the callback function is provided then gnutls will call it, in the
  * handshake, after the certificate request message has been received.
  *
  * The callback function should set the certificate list to be sent, and
  * return 0 on success. If no certificate was selected then the number of certificates
  * should be set to zero. The value (-1) indicates error and the handshake
  * will be terminated.
  **/
void MHD_gtls_certificate_client_set_retrieve_function
  (MHD_gtls_cert_credentials_t cred,
   MHD_gnutls_certificate_client_retrieve_function * func)
{
  cred->client_get_cert_callback = func;
}

/**
  * MHD_gtls_certificate_server_set_retrieve_function - Used to set a callback to retrieve the certificate
  * @cred: is a #MHD_gtls_cert_credentials_t structure.
  * @func: is the callback function
  *
  * This function sets a callback to be called in order to retrieve the certificate
  * to be used in the handshake.
  * The callback's function prototype is:
  * int (*callback)(MHD_gtls_session_t, MHD_gnutls_retr_st* st);
  *
  * @st should contain the certificates and private keys.
  *
  * If the callback function is provided then gnutls will call it, in the
  * handshake, after the certificate request message has been received.
  *
  * The callback function should set the certificate list to be sent, and
  * return 0 on success.  The value (-1) indicates error and the handshake
  * will be terminated.
  **/
void MHD_gtls_certificate_server_set_retrieve_function
  (MHD_gtls_cert_credentials_t cred,
   MHD_gnutls_certificate_server_retrieve_function * func)
{
  cred->server_get_cert_callback = func;
}

/*-
 * MHD__gnutls_x509_extract_certificate_activation_time - This function returns the peer's certificate activation time
 * @cert: should contain an X.509 DER encoded certificate
 *
 * This function will return the certificate's activation time in UNIX time
 * (ie seconds since 00:00:00 UTC January 1, 1970).
 *
 * Returns a (time_t) -1 in case of an error.
 *
 -*/
static time_t
MHD__gnutls_x509_get_raw_crt_activation_time (const MHD_gnutls_datum_t * cert)
{
  MHD_gnutls_x509_crt_t xcert;
  time_t result;

  result = MHD_gnutls_x509_crt_init (&xcert);
  if (result < 0)
    return (time_t) - 1;

  result = MHD_gnutls_x509_crt_import (xcert, cert, GNUTLS_X509_FMT_DER);
  if (result < 0)
    {
      MHD_gnutls_x509_crt_deinit (xcert);
      return (time_t) - 1;
    }

  result = MHD_gnutls_x509_crt_get_activation_time (xcert);

  MHD_gnutls_x509_crt_deinit (xcert);

  return result;
}

/*-
 * MHD_gnutls_x509_extract_certificate_expiration_time - This function returns the certificate's expiration time
 * @cert: should contain an X.509 DER encoded certificate
 *
 * This function will return the certificate's expiration time in UNIX
 * time (ie seconds since 00:00:00 UTC January 1, 1970).  Returns a
 *
 * (time_t) -1 in case of an error.
 *
 -*/
static time_t
MHD__gnutls_x509_get_raw_crt_expiration_time (const MHD_gnutls_datum_t * cert)
{
  MHD_gnutls_x509_crt_t xcert;
  time_t result;

  result = MHD_gnutls_x509_crt_init (&xcert);
  if (result < 0)
    return (time_t) - 1;

  result = MHD_gnutls_x509_crt_import (xcert, cert, GNUTLS_X509_FMT_DER);
  if (result < 0)
    {
      MHD_gnutls_x509_crt_deinit (xcert);
      return (time_t) - 1;
    }

  result = MHD_gnutls_x509_crt_get_expiration_time (xcert);

  MHD_gnutls_x509_crt_deinit (xcert);

  return result;
}

/**
  * MHD_gtls_certificate_verify_peers2 - This function returns the peer's certificate verification status
  * @session: is a gnutls session
  * @status: is the output of the verification
  *
  * This function will try to verify the peer's certificate and return
  * its status (trusted, invalid etc.).  The value of @status should
  * be one or more of the MHD_gnutls_certificate_status_t enumerated
  * elements bitwise or'd. To avoid denial of service attacks some
  * default upper limits regarding the certificate key size and chain
  * size are set. To override them use
  * MHD__gnutls_certificate_set_verify_limits().
  *
  * Note that you must also check the peer's name in order to check if
  * the verified certificate belongs to the actual peer.
  *
  * This is the same as MHD_gnutls_x509_crt_list_verify() and uses the
  * loaded CAs in the credentials as trusted CAs.
  *
  * Note that some commonly used X.509 Certificate Authorities are
  * still using Version 1 certificates.  If you want to accept them,
  * you need to call MHD__gnutls_certificate_set_verify_flags() with, e.g.,
  * %GNUTLS_VERIFY_ALLOW_X509_V1_CA_CRT parameter.
  *
  * Returns: a negative error code on error and zero on success.
  **/
int
MHD_gtls_certificate_verify_peers2 (MHD_gtls_session_t session,
                                    unsigned int *status)
{
  cert_auth_info_t info;

  CHECK_AUTH (MHD_GNUTLS_CRD_CERTIFICATE, GNUTLS_E_INVALID_REQUEST);

  info = MHD_gtls_get_auth_info (session);
  if (info == NULL)
    {
      return GNUTLS_E_NO_CERTIFICATE_FOUND;
    }

  if (info->raw_certificate_list == NULL || info->ncerts == 0)
    return GNUTLS_E_NO_CERTIFICATE_FOUND;

  switch (MHD_gnutls_certificate_type_get (session))
    {
    case MHD_GNUTLS_CRT_X509:
      return MHD__gnutls_x509_cert_verify_peers (session, status);
    default:
      return GNUTLS_E_INVALID_REQUEST;
    }
}

/**
  * MHD_gtls_certificate_verify_peers - This function returns the peer's certificate verification status
  * @session: is a gnutls session
  *
  * This function will try to verify the peer's certificate and return
  * its status (trusted, invalid etc.).  However you must also check
  * the peer's name in order to check if the verified certificate
  * belongs to the actual peer.
  *
  * The return value should be one or more of the
  * MHD_gnutls_certificate_status_t enumerated elements bitwise or'd, or a
  * negative value on error.
  *
  * This is the same as MHD_gnutls_x509_crt_list_verify().
  *
  * Deprecated: Use MHD_gtls_certificate_verify_peers2() instead.
  **/
int
MHD_gtls_certificate_verify_peers (MHD_gtls_session_t session)
{
  unsigned int status;
  int ret;

  ret = MHD_gtls_certificate_verify_peers2 (session, &status);

  if (ret < 0)
    {
      MHD_gnutls_assert ();
      return ret;
    }

  return status;
}

/**
  * MHD_gtls_certificate_expiration_time_peers - This function returns the peer's certificate expiration time
  * @session: is a gnutls session
  *
  * This function will return the peer's certificate expiration time.
  *
  * Returns: (time_t)-1 on error.
  **/
time_t
MHD_gtls_certificate_expiration_time_peers (MHD_gtls_session_t session)
{
  cert_auth_info_t info;

  CHECK_AUTH (MHD_GNUTLS_CRD_CERTIFICATE, GNUTLS_E_INVALID_REQUEST);

  info = MHD_gtls_get_auth_info (session);
  if (info == NULL)
    {
      return (time_t) - 1;
    }

  if (info->raw_certificate_list == NULL || info->ncerts == 0)
    {
      MHD_gnutls_assert ();
      return (time_t) - 1;
    }

  switch (MHD_gnutls_certificate_type_get (session))
    {
    case MHD_GNUTLS_CRT_X509:
      return
        MHD__gnutls_x509_get_raw_crt_expiration_time (&info->
                                                      raw_certificate_list
                                                      [0]);
    default:
      return (time_t) - 1;
    }
}

/**
  * MHD_gtls_certificate_activation_time_peers - This function returns the peer's certificate activation time
  * @session: is a gnutls session
  *
  * This function will return the peer's certificate activation time.
  * This is the creation time for openpgp keys.
  *
  * Returns: (time_t)-1 on error.
  **/
time_t
MHD_gtls_certificate_activation_time_peers (MHD_gtls_session_t session)
{
  cert_auth_info_t info;

  CHECK_AUTH (MHD_GNUTLS_CRD_CERTIFICATE, GNUTLS_E_INVALID_REQUEST);

  info = MHD_gtls_get_auth_info (session);
  if (info == NULL)
    {
      return (time_t) - 1;
    }

  if (info->raw_certificate_list == NULL || info->ncerts == 0)
    {
      MHD_gnutls_assert ();
      return (time_t) - 1;
    }

  switch (MHD_gnutls_certificate_type_get (session))
    {
    case MHD_GNUTLS_CRT_X509:
      return
        MHD__gnutls_x509_get_raw_crt_activation_time (&info->
                                                      raw_certificate_list
                                                      [0]);
    default:
      return (time_t) - 1;
    }
}

int
MHD_gtls_raw_cert_to_gcert (MHD_gnutls_cert * gcert,
                            enum MHD_GNUTLS_CertificateType type,
                            const MHD_gnutls_datum_t * raw_cert,
                            int flags /* OR of ConvFlags */ )
{
  switch (type)
    {
    case MHD_GNUTLS_CRT_X509:
      return MHD_gtls_x509_raw_cert_to_gcert (gcert, raw_cert, flags);
    default:
      MHD_gnutls_assert ();
      return GNUTLS_E_INTERNAL_ERROR;
    }
}

int
MHD_gtls_raw_privkey_to_gkey (MHD_gnutls_privkey * key,
                              enum MHD_GNUTLS_CertificateType type,
                              const MHD_gnutls_datum_t * raw_key,
                              int key_enc /* DER or PEM */ )
{
  switch (type)
    {
    case MHD_GNUTLS_CRT_X509:
      return MHD__gnutls_x509_raw_privkey_to_gkey (key, raw_key, key_enc);
    default:
      MHD_gnutls_assert ();
      return GNUTLS_E_INTERNAL_ERROR;
    }
}


/* This function will convert a der certificate to a format
 * (structure) that gnutls can understand and use. Actually the
 * important thing on this function is that it extracts the
 * certificate's (public key) parameters.
 *
 * The noext flag is used to complete the handshake even if the
 * extensions found in the certificate are unsupported and critical.
 * The critical extensions will be catched by the verification functions.
 */
int
MHD_gtls_x509_raw_cert_to_gcert (MHD_gnutls_cert * gcert,
                                 const MHD_gnutls_datum_t * derCert,
                                 int flags /* OR of ConvFlags */ )
{
  int ret;
  MHD_gnutls_x509_crt_t cert;

  ret = MHD_gnutls_x509_crt_init (&cert);
  if (ret < 0)
    {
      MHD_gnutls_assert ();
      return ret;
    }

  ret = MHD_gnutls_x509_crt_import (cert, derCert, GNUTLS_X509_FMT_DER);
  if (ret < 0)
    {
      MHD_gnutls_assert ();
      MHD_gnutls_x509_crt_deinit (cert);
      return ret;
    }

  ret = MHD_gtls_x509_crt_to_gcert (gcert, cert, flags);
  MHD_gnutls_x509_crt_deinit (cert);

  return ret;
}

/* Like above but it accepts a parsed certificate instead.
 */
int
MHD_gtls_x509_crt_to_gcert (MHD_gnutls_cert * gcert,
                            MHD_gnutls_x509_crt_t cert, unsigned int flags)
{
  int ret = 0;

  memset (gcert, 0, sizeof (MHD_gnutls_cert));
  gcert->cert_type = MHD_GNUTLS_CRT_X509;

  if (!(flags & CERT_NO_COPY))
    {
#define SMALL_DER 512
      opaque *der;
      size_t der_size = SMALL_DER;

      /* initially allocate a bogus size, just in case the certificate
       * fits in it. That way we minimize the DER encodings performed.
       */
      der = MHD_gnutls_malloc (SMALL_DER);
      if (der == NULL)
        {
          MHD_gnutls_assert ();
          return GNUTLS_E_MEMORY_ERROR;
        }

      ret =
        MHD_gnutls_x509_crt_export (cert, GNUTLS_X509_FMT_DER, der,
                                    &der_size);
      if (ret < 0 && ret != GNUTLS_E_SHORT_MEMORY_BUFFER)
        {
          MHD_gnutls_assert ();
          MHD_gnutls_free (der);
          return ret;
        }

      if (ret == GNUTLS_E_SHORT_MEMORY_BUFFER)
        {
          der = MHD_gnutls_realloc (der, der_size);
          if (der == NULL)
            {
              MHD_gnutls_assert ();
              return GNUTLS_E_MEMORY_ERROR;
            }

          ret =
            MHD_gnutls_x509_crt_export (cert, GNUTLS_X509_FMT_DER, der,
                                        &der_size);
          if (ret < 0)
            {
              MHD_gnutls_assert ();
              MHD_gnutls_free (der);
              return ret;
            }
        }

      gcert->raw.data = der;
      gcert->raw.size = der_size;
    }
  else
    /* now we have 0 or a bitwise or of things to decode */
    flags ^= CERT_NO_COPY;


  if (flags & CERT_ONLY_EXTENSIONS || flags == 0)
    {
      MHD_gnutls_x509_crt_get_key_usage (cert, &gcert->key_usage, NULL);
      gcert->version = MHD_gnutls_x509_crt_get_version (cert);
    }
  gcert->subject_pk_algorithm =
    MHD_gnutls_x509_crt_get_pk_algorithm (cert, NULL);

  if (flags & CERT_ONLY_PUBKEY || flags == 0)
    {
      gcert->params_size = MAX_PUBLIC_PARAMS_SIZE;
      ret =
        MHD__gnutls_x509_crt_get_mpis (cert, gcert->params,
                                       &gcert->params_size);
      if (ret < 0)
        {
          MHD_gnutls_assert ();
          return ret;
        }
    }

  return 0;

}

void
MHD_gtls_gcert_deinit (MHD_gnutls_cert * cert)
{
  int i;

  if (cert == NULL)
    return;

  for (i = 0; i < cert->params_size; i++)
    {
      MHD_gtls_mpi_release (&cert->params[i]);
    }

  MHD__gnutls_free_datum (&cert->raw);
}

/**
 * MHD_gtls_sign_callback_set:
 * @session: is a gnutls session
 * @sign_func: function pointer to application's sign callback.
 * @userdata: void pointer that will be passed to sign callback.
 *
 * Set the callback function.  The function must have this prototype:
 *
 * typedef int (*MHD_gnutls_sign_func) (MHD_gtls_session_t session,
 *                                  void *userdata,
 *                                  enum MHD_GNUTLS_CertificateType cert_type,
 *                                  const MHD_gnutls_datum_t * cert,
 *                                  const MHD_gnutls_datum_t * hash,
 *                                  MHD_gnutls_datum_t * signature);
 *
 * The @userdata parameter is passed to the @sign_func verbatim, and
 * can be used to store application-specific data needed in the
 * callback function.  See also MHD_gtls_sign_callback_get().
 **/
void
MHD_gtls_sign_callback_set (MHD_gtls_session_t session,
                            MHD_gnutls_sign_func sign_func, void *userdata)
{
  session->internals.sign_func = sign_func;
  session->internals.sign_func_userdata = userdata;
}

/**
 * MHD_gtls_sign_callback_get:
 * @session: is a gnutls session
 * @userdata: if non-%NULL, will be set to abstract callback pointer.
 *
 * Retrieve the callback function, and its userdata pointer.
 *
 * Returns: The function pointer set by MHD_gtls_sign_callback_set(), or
 *   if not set, %NULL.
 **/
MHD_gnutls_sign_func
MHD_gtls_sign_callback_get (MHD_gtls_session_t session, void **userdata)
{
  if (userdata)
    *userdata = session->internals.sign_func_userdata;
  return session->internals.sign_func;
}