imap_auth_res_t imap_auth_gss (IMAP_DATA* idata, const char* method)
{
  gss_buffer_desc request_buf, send_token;
  gss_buffer_t sec_token;
  gss_name_t target_name;
  gss_ctx_id_t context;
#ifdef DEBUG
  gss_OID mech_name;
  char server_conf_flags;
#endif
  gss_qop_t quality;
  int cflags;
  OM_uint32 maj_stat, min_stat;
  char buf1[GSS_BUFSIZE], buf2[GSS_BUFSIZE];
  unsigned long buf_size;
  int rc;

  if (!mutt_bit_isset (idata->capabilities, AGSSAPI))
    return IMAP_AUTH_UNAVAIL;

  if (mutt_account_getuser (&idata->conn->account))
    return IMAP_AUTH_FAILURE;
  
  /* get an IMAP service ticket for the server */
  snprintf (buf1, sizeof (buf1), "imap@%s", idata->conn->account.host);
  request_buf.value = buf1;
  request_buf.length = strlen (buf1);
  maj_stat = gss_import_name (&min_stat, &request_buf, gss_nt_service_name,
    &target_name);
  if (maj_stat != GSS_S_COMPLETE)
  {
    dprint (2, (debugfile, "Couldn't get service name for [%s]\n", buf1));
    return IMAP_AUTH_UNAVAIL;
  }
#ifdef DEBUG	
  else if (debuglevel >= 2)
  {
    maj_stat = gss_display_name (&min_stat, target_name, &request_buf,
      &mech_name);
    dprint (2, (debugfile, "Using service name [%s]\n",
      (char*) request_buf.value));
    maj_stat = gss_release_buffer (&min_stat, &request_buf);
  }
#endif
  /* Acquire initial credentials - without a TGT GSSAPI is UNAVAIL */
  sec_token = GSS_C_NO_BUFFER;
  context = GSS_C_NO_CONTEXT;

  /* build token */
  maj_stat = gss_init_sec_context (&min_stat, GSS_C_NO_CREDENTIAL, &context,
    target_name, GSS_C_NO_OID, GSS_C_MUTUAL_FLAG | GSS_C_SEQUENCE_FLAG, 0, 
    GSS_C_NO_CHANNEL_BINDINGS, sec_token, NULL, &send_token,
    (unsigned int*) &cflags, NULL);
  if (maj_stat != GSS_S_COMPLETE && maj_stat != GSS_S_CONTINUE_NEEDED)
  {
    print_gss_error(maj_stat, min_stat);
    dprint (1, (debugfile, "Error acquiring credentials - no TGT?\n"));
    gss_release_name (&min_stat, &target_name);

    return IMAP_AUTH_UNAVAIL;
  }

  /* now begin login */
  mutt_message _("Authenticating (GSSAPI)...");

  imap_cmd_start (idata, "AUTHENTICATE GSSAPI");

  /* expect a null continuation response ("+") */
  do
    rc = imap_cmd_step (idata);
  while (rc == IMAP_CMD_CONTINUE);

  if (rc != IMAP_CMD_RESPOND)
  {
    dprint (2, (debugfile, "Invalid response from server: %s\n", buf1));
    gss_release_name (&min_stat, &target_name);
    goto bail;
  }

  /* now start the security context initialisation loop... */
  dprint (2, (debugfile, "Sending credentials\n"));
  mutt_to_base64 ((unsigned char*) buf1, send_token.value, send_token.length,
    sizeof (buf1) - 2);
  gss_release_buffer (&min_stat, &send_token);
  safe_strcat (buf1, sizeof (buf1), "\r\n");
  mutt_socket_write (idata->conn, buf1);

  while (maj_stat == GSS_S_CONTINUE_NEEDED)
  {
    /* Read server data */
    do
      rc = imap_cmd_step (idata);
    while (rc == IMAP_CMD_CONTINUE);

    if (rc != IMAP_CMD_RESPOND)
    {
      dprint (1, (debugfile, "Error receiving server response.\n"));
      gss_release_name (&min_stat, &target_name);
      goto bail;
    }

    request_buf.length = mutt_from_base64 (buf2, idata->buf + 2, sizeof(buf2));
    request_buf.value = buf2;
    sec_token = &request_buf;

    /* Write client data */
    maj_stat = gss_init_sec_context (&min_stat, GSS_C_NO_CREDENTIAL, &context,
      target_name, GSS_C_NO_OID, GSS_C_MUTUAL_FLAG | GSS_C_SEQUENCE_FLAG, 0, 
      GSS_C_NO_CHANNEL_BINDINGS, sec_token, NULL, &send_token,
      (unsigned int*) &cflags, NULL);
    if (maj_stat != GSS_S_COMPLETE && maj_stat != GSS_S_CONTINUE_NEEDED)
    {
      print_gss_error(maj_stat, min_stat);
      dprint (1, (debugfile, "Error exchanging credentials\n"));
      gss_release_name (&min_stat, &target_name);

      goto err_abort_cmd;
    }
    mutt_to_base64 ((unsigned char*) buf1, send_token.value,
      send_token.length, sizeof (buf1) - 2);
    gss_release_buffer (&min_stat, &send_token);
    safe_strcat (buf1, sizeof (buf1), "\r\n");
    mutt_socket_write (idata->conn, buf1);
  }

  gss_release_name (&min_stat, &target_name);

  /* get security flags and buffer size */
  do
    rc = imap_cmd_step (idata);
  while (rc == IMAP_CMD_CONTINUE);

  if (rc != IMAP_CMD_RESPOND)
  {
    dprint (1, (debugfile, "Error receiving server response.\n"));
    goto bail;
  }
  request_buf.length = mutt_from_base64 (buf2, idata->buf + 2, sizeof(buf2));
  request_buf.value = buf2;

  maj_stat = gss_unwrap (&min_stat, context, &request_buf, &send_token,
    &cflags, &quality);
  if (maj_stat != GSS_S_COMPLETE)
  {
    print_gss_error(maj_stat, min_stat);
    dprint (2, (debugfile, "Couldn't unwrap security level data\n"));
    gss_release_buffer (&min_stat, &send_token);
    goto err_abort_cmd;
  }
  dprint (2, (debugfile, "Credential exchange complete\n"));

  /* first octet is security levels supported. We want NONE */
#ifdef DEBUG
  server_conf_flags = ((char*) send_token.value)[0];
#endif
  if ( !(((char*) send_token.value)[0] & GSS_AUTH_P_NONE) )
  {
    dprint (2, (debugfile, "Server requires integrity or privacy\n"));
    gss_release_buffer (&min_stat, &send_token);
    goto err_abort_cmd;
  }

  /* we don't care about buffer size if we don't wrap content. But here it is */
  ((char*) send_token.value)[0] = 0;
  buf_size = ntohl (*((long *) send_token.value));
  gss_release_buffer (&min_stat, &send_token);
  dprint (2, (debugfile, "Unwrapped security level flags: %c%c%c\n",
    server_conf_flags & GSS_AUTH_P_NONE      ? 'N' : '-',
    server_conf_flags & GSS_AUTH_P_INTEGRITY ? 'I' : '-',
    server_conf_flags & GSS_AUTH_P_PRIVACY   ? 'P' : '-'));
  dprint (2, (debugfile, "Maximum GSS token size is %ld\n", buf_size));

  /* agree to terms (hack!) */
  buf_size = htonl (buf_size); /* not relevant without integrity/privacy */
  memcpy (buf1, &buf_size, 4);
  buf1[0] = GSS_AUTH_P_NONE;
  /* server decides if principal can log in as user */
  strncpy (buf1 + 4, idata->conn->account.user, sizeof (buf1) - 4);
  request_buf.value = buf1;
  request_buf.length = 4 + strlen (idata->conn->account.user);
  maj_stat = gss_wrap (&min_stat, context, 0, GSS_C_QOP_DEFAULT, &request_buf,
    &cflags, &send_token);
  if (maj_stat != GSS_S_COMPLETE)
  {
    dprint (2, (debugfile, "Error creating login request\n"));
    goto err_abort_cmd;
  }

  mutt_to_base64 ((unsigned char*) buf1, send_token.value, send_token.length,
		  sizeof (buf1) - 2);
  dprint (2, (debugfile, "Requesting authorisation as %s\n",
    idata->conn->account.user));
  safe_strcat (buf1, sizeof (buf1), "\r\n");
  mutt_socket_write (idata->conn, buf1);

  /* Joy of victory or agony of defeat? */
  do
    rc = imap_cmd_step (idata);
  while (rc == IMAP_CMD_CONTINUE);
  if (rc == IMAP_CMD_RESPOND)
  {
    dprint (1, (debugfile, "Unexpected server continuation request.\n"));
    goto err_abort_cmd;
  }
  if (imap_code (idata->buf))
  {
    /* flush the security context */
    dprint (2, (debugfile, "Releasing GSS credentials\n"));
    maj_stat = gss_delete_sec_context (&min_stat, &context, &send_token);
    if (maj_stat != GSS_S_COMPLETE)
      dprint (1, (debugfile, "Error releasing credentials\n"));

    /* send_token may contain a notification to the server to flush
     * credentials. RFC 1731 doesn't specify what to do, and since this
     * support is only for authentication, we'll assume the server knows
     * enough to flush its own credentials */
    gss_release_buffer (&min_stat, &send_token);

    return IMAP_AUTH_SUCCESS;
  }
  else
    goto bail;

 err_abort_cmd:
  mutt_socket_write (idata->conn, "*\r\n");
  do
    rc = imap_cmd_step (idata);
  while (rc == IMAP_CMD_CONTINUE);

 bail:
  mutt_error _("GSSAPI authentication failed.");
  mutt_sleep (2);
  return IMAP_AUTH_FAILURE;
}