/* GNU mailutils - a suite of utilities for electronic mail
   Copyright (C) 1999, 2001 Free Software Foundation, Inc.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2, or (at your option)
   any later version.

   This program 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 General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.  */

/* GSSAPI authentication for imap (rfc 1731). 
 */

#include "imap4d.h"

#include <netinet/in.h>

#include <krb5.h>
#include <gssapi/gssapi.h>
#include <gssapi/gssapi_generic.h>

#define GSS_AUTH_P_NONE      1
#define GSS_AUTH_P_INTEGRITY 2
#define GSS_AUTH_P_PRIVACY   4

#define SUPPORTED_P_MECH GSS_AUTH_P_NONE
static int protection_mech;
size_t server_buffer_size = 8192;
size_t client_buffer_size;

static void
display_status_1 (char *m, OM_uint32 code, int type)
{
  OM_uint32 maj_stat, min_stat;
  gss_buffer_desc msg;
  OM_uint32 msg_ctx;

  msg_ctx = 0;
  do
    {
      maj_stat = gss_display_status (&min_stat, code,
				     type, GSS_C_NULL_OID,
				     &msg_ctx, &msg);
      syslog (LOG_ERR,
	      "GSS-API error %s: %s\n", m,
	      (char *)msg.value);
      gss_release_buffer (&min_stat, &msg);
    }
  while (msg_ctx);
}

static void
display_status (char *msg, OM_uint32 maj_stat, OM_uint32 min_stat)
{
  display_status_1 (msg, maj_stat, GSS_C_GSS_CODE);
  display_status_1 (msg, min_stat, GSS_C_MECH_CODE);
}

static int
imap4d_gss_userok(gss_buffer_t client_name, char *name)
{
  int rc = -1;
  krb5_principal p;
  krb5_context kcontext;
  
  krb5_init_context (&kcontext);
  
  if (krb5_parse_name (kcontext, client_name->value, &p) != 0)
    return -1;
  if (krb5_kuserok (kcontext, p, name))
    rc = 0;
  else
    rc = 1;
  krb5_free_principal (kcontext, p);
  return rc;
}

int
auth_gssapi (struct imap4d_command *command, char **username)
{
  gss_buffer_desc tokbuf, outbuf;
  OM_uint32 maj_stat, min_stat, min_stat2;
  OM_uint32 cflags;
  OM_uint32 sec_level, mech;
  gss_ctx_id_t context;
  gss_cred_id_t cred_handle, server_creds;
  gss_OID mech_type;
  char *token_str;
  unsigned char *tmp = NULL;
  size_t size;
  gss_name_t server_name;
  gss_qop_t quality;
  gss_name_t client;
  gss_buffer_desc client_name;
  
  /* Obtain server credentials. RFC 1732 states, that 
      "The server must issue a ready response with no data and pass the
       resulting client supplied token to GSS_Accept_sec_context as
       input_token, setting acceptor_cred_handle to NULL (for "use default
       credentials"), and 0 for input_context_handle (initially)."
     In MIT implementation, passing NULL as acceptor_cred_handle won't
     work (possibly due to a bug in krb5_gss_accept_sec_context()), so
     we acquire server credentials explicitly. */
     
  asprintf ((char**)&tmp, "imap@%s", util_localname ());
  tokbuf.value = tmp;
  tokbuf.length = strlen (tokbuf.value) + 1;
  maj_stat = gss_import_name (&min_stat, &tokbuf,
			      gss_nt_service_name,
			      &server_name);
  if (maj_stat != GSS_S_COMPLETE)
    {
      display_status ("import name", maj_stat, min_stat);
      util_finish (command, RESP_NO,
		   "GSSAPI authentication not available");
      return 1;
    }
  
  maj_stat = gss_acquire_cred (&min_stat, server_name, 0,
			       GSS_C_NULL_OID_SET, GSS_C_ACCEPT,
			       &server_creds, NULL, NULL);
  gss_release_name(&min_stat2, &server_name);
  
  if (maj_stat != GSS_S_COMPLETE)
    {
      display_status ("acquire credentials", maj_stat, min_stat);
      util_finish (command, RESP_NO,
		   "GSSAPI authentication not available");
      return 1;
    }

  /* Start the dialogue */
  
  util_send ("+ GO AHEAD\r\n");
  
  context = GSS_C_NO_CONTEXT;
 
  for (;;)
    {
      token_str = imap4d_readline_ex (ifile);
      util_base64_decode (token_str, strlen (token_str), &tmp, &size);
      tokbuf.value = tmp;
      tokbuf.length = size;
      free (token_str);
      
      maj_stat = gss_accept_sec_context (&min_stat,
					 &context,
					 server_creds,
					 &tokbuf,
					 GSS_C_NO_CHANNEL_BINDINGS,
					 &client,
					 &mech_type,
					 &outbuf,
					 &cflags,
					 NULL,
					 &cred_handle);
      free (tmp);
      if (maj_stat == GSS_S_CONTINUE_NEEDED)
	{
	  if (outbuf.length)
	    {
	      util_base64_encode (outbuf.value, outbuf.length, &tmp, &size);
	      util_send ("+ %*.*s\r\n", size, size, tmp);
	      free (tmp);
	      gss_release_buffer (&min_stat, &outbuf);
	    }
	  continue;
	}
      else if (maj_stat == GSS_S_COMPLETE)
	break;
      /* Bail out otherwise */
      
      display_status ("accept context", maj_stat, min_stat);
      maj_stat = gss_delete_sec_context (&min_stat, &context, &outbuf);
      gss_release_buffer (&min_stat, &outbuf);
      util_finish (command, RESP_NO,
		   "GSSAPI authentication failed");
      return 1;
    }

  if (outbuf.length)
    {
      util_base64_encode (outbuf.value, outbuf.length, &tmp, &size);
      util_send ("+ %*.*s\r\n", size, size, tmp);
      free (tmp);
      gss_release_buffer (&min_stat, &outbuf);
      token_str = imap4d_readline_ex (ifile);
      free (token_str);
    }

  /* Construct security-level data */
  sec_level = htonl ((SUPPORTED_P_MECH << 24) | server_buffer_size);
  tokbuf.length = 4;
  tokbuf.value = &sec_level;
  gss_wrap (&min_stat, context, 0, GSS_C_QOP_DEFAULT,
	    &tokbuf, &cflags, &outbuf);
  util_base64_encode (outbuf.value, outbuf.length, &tmp, &size);
  util_send ("+ %*.*s\r\n", size, size, tmp);
  free (tmp);

  token_str = imap4d_readline_ex (ifile);
  util_base64_decode (token_str, strlen (token_str),
		      (unsigned char **)&tokbuf.value, &tokbuf.length);
  free (token_str);
  
  gss_unwrap (&min_stat, context, &tokbuf, &outbuf, &cflags, &quality);
  free (tokbuf.value);
  
  sec_level = ntohl (*(OM_uint32*)outbuf.value);

  /* FIXME: parse sec_level and act accordingly to its settings */
  mech = sec_level >> 24;
  if ((mech & SUPPORTED_P_MECH) == 0)
    {
      syslog (LOG_NOTICE,
	      "client requested unsupported protection mechanism (%d)",
	      mech);
      gss_release_buffer (&min_stat, &outbuf);
      maj_stat = gss_delete_sec_context (&min_stat, &context, &outbuf);
      gss_release_buffer (&min_stat, &outbuf);
      util_finish (command, RESP_NO,
	  "GSSAPI authentication failed: unsupported protection mechanism");
      return 1;
    }
  protection_mech = mech;
  client_buffer_size = sec_level & 0x00ffffffff;

  *username = strdup ((char*)outbuf.value + 4);
  gss_release_buffer (&min_stat, &outbuf);

  maj_stat = gss_display_name(&min_stat, client,
			      &client_name, &mech_type);
  if (maj_stat != GSS_S_COMPLETE)
    {
      display_status ("get client name", maj_stat, min_stat);
      maj_stat = gss_delete_sec_context (&min_stat, &context, &outbuf);
      gss_release_buffer (&min_stat, &outbuf);
      free (*username);
      util_finish (command, RESP_NO,
		   "GSSAPI authentication failed");
      return 1;
    }

  if (imap4d_gss_userok (&client_name, *username))
    {
      syslog (LOG_NOTICE, "GSSAPI user %s is NOT authorized as %s",
	      (char *) client_name.value, *username);
      util_finish (command, RESP_NO,
		   "GSSAPI user %s is NOT authorized as %s",
		   client_name.value, *username);
      maj_stat = gss_delete_sec_context (&min_stat, &context, &outbuf);
      gss_release_buffer (&min_stat, &outbuf);
      gss_release_buffer (&min_stat, &client_name);
      free (*username);
      return 1;
    }
  else
    {
      syslog (LOG_NOTICE, "GSSAPI user %s is authorized as %s",
	      (char *) client_name.value, *username);
    }

  gss_release_buffer (&min_stat, &client_name);
  maj_stat = gss_delete_sec_context (&min_stat, &context, &outbuf);
  gss_release_buffer (&min_stat, &outbuf);
  util_finish (command, RESP_OK,
	       "GSSAPI authentication successful");
  return 0;
}