dbus-auth.c

/* -*- mode: C; c-file-style: "gnu" -*- */
/* dbus-auth.c Authentication
 *
 * Copyright (C) 2002, 2003, 2004 Red Hat Inc.
 *
 * Licensed under the Academic Free License version 2.1
 * 
 * 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 of the License, 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., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 */
#include "dbus-auth.h"
#include "dbus-string.h"
#include "dbus-list.h"
#include "dbus-internals.h"
#include "dbus-keyring.h"
#include "dbus-sha.h"
#include "dbus-protocol.h"
#include "dbus-userdb.h"

typedef dbus_bool_t (* DBusInitialResponseFunction)  (DBusAuth         *auth,
                                                      DBusString       *response);

typedef dbus_bool_t (* DBusAuthDataFunction)     (DBusAuth         *auth,
                                                  const DBusString *data);

typedef dbus_bool_t (* DBusAuthEncodeFunction)   (DBusAuth         *auth,
                                                  const DBusString *data,
                                                  DBusString       *encoded);

typedef dbus_bool_t (* DBusAuthDecodeFunction)   (DBusAuth         *auth,
                                                  const DBusString *data,
                                                  DBusString       *decoded);

typedef void        (* DBusAuthShutdownFunction) (DBusAuth       *auth);

typedef struct
{
  const char *mechanism; 
  DBusAuthDataFunction server_data_func; 
  DBusAuthEncodeFunction server_encode_func; 
  DBusAuthDecodeFunction server_decode_func; 
  DBusAuthShutdownFunction server_shutdown_func; 
  DBusInitialResponseFunction client_initial_response_func; 
  DBusAuthDataFunction client_data_func; 
  DBusAuthEncodeFunction client_encode_func; 
  DBusAuthDecodeFunction client_decode_func; 
  DBusAuthShutdownFunction client_shutdown_func; 
} DBusAuthMechanismHandler;

typedef enum {
  DBUS_AUTH_COMMAND_AUTH,
  DBUS_AUTH_COMMAND_CANCEL,
  DBUS_AUTH_COMMAND_DATA,
  DBUS_AUTH_COMMAND_BEGIN,
  DBUS_AUTH_COMMAND_REJECTED,
  DBUS_AUTH_COMMAND_OK,
  DBUS_AUTH_COMMAND_ERROR,
  DBUS_AUTH_COMMAND_UNKNOWN
} DBusAuthCommand;

typedef dbus_bool_t (* DBusAuthStateFunction) (DBusAuth         *auth,
                                               DBusAuthCommand   command,
                                               const DBusString *args);

typedef struct
{
  const char *name;               
  DBusAuthStateFunction handler;  
} DBusAuthStateData;

struct DBusAuth
{
  int refcount;           
  const char *side;       
  DBusString incoming;    
  DBusString outgoing;    
  const DBusAuthStateData *state;         
  const DBusAuthMechanismHandler *mech;   
  DBusString identity;                   
  DBusCredentials credentials;      
  DBusCredentials authorized_identity; 
  DBusCredentials desired_identity;    
  DBusString context;               
  DBusKeyring *keyring;             
  int cookie_id;                    
  DBusString challenge;             
  char **allowed_mechs;             
  unsigned int needed_memory : 1;   
  unsigned int already_got_mechanisms : 1;       
  unsigned int already_asked_for_initial_response : 1; 
  unsigned int buffer_outstanding : 1; 
};

typedef struct
{
  DBusAuth base;    
  DBusList *mechs_to_try; 
  DBusString guid_from_server; 
} DBusAuthClient;

typedef struct
{
  DBusAuth base;    
  int failures;     
  int max_failures; 
  DBusString guid;  
} DBusAuthServer;

static void        goto_state                (DBusAuth                       *auth,
                                              const DBusAuthStateData        *new_state);
static dbus_bool_t send_auth                 (DBusAuth *auth,
                                              const DBusAuthMechanismHandler *mech);
static dbus_bool_t send_data                 (DBusAuth *auth,
                                              DBusString *data);
static dbus_bool_t send_rejected             (DBusAuth *auth);
static dbus_bool_t send_error                (DBusAuth *auth,
                                              const char *message);
static dbus_bool_t send_ok                   (DBusAuth *auth);
static dbus_bool_t send_begin                (DBusAuth *auth,
                                              const DBusString *args_from_ok);
static dbus_bool_t send_cancel               (DBusAuth *auth);

static dbus_bool_t handle_server_state_waiting_for_auth  (DBusAuth         *auth,
                                                          DBusAuthCommand   command,
                                                          const DBusString *args);
static dbus_bool_t handle_server_state_waiting_for_data  (DBusAuth         *auth,
                                                          DBusAuthCommand   command,
                                                          const DBusString *args);
static dbus_bool_t handle_server_state_waiting_for_begin (DBusAuth         *auth,
                                                          DBusAuthCommand   command,
                                                          const DBusString *args);
  
static const DBusAuthStateData server_state_waiting_for_auth = {
  "WaitingForAuth", handle_server_state_waiting_for_auth
};
static const DBusAuthStateData server_state_waiting_for_data = {
  "WaitingForData", handle_server_state_waiting_for_data
};
static const DBusAuthStateData server_state_waiting_for_begin = {
  "WaitingForBegin", handle_server_state_waiting_for_begin
};
  
static dbus_bool_t handle_client_state_waiting_for_data   (DBusAuth         *auth,
                                                           DBusAuthCommand   command,
                                                           const DBusString *args);
static dbus_bool_t handle_client_state_waiting_for_ok     (DBusAuth         *auth,
                                                           DBusAuthCommand   command,
                                                           const DBusString *args);
static dbus_bool_t handle_client_state_waiting_for_reject (DBusAuth         *auth,
                                                           DBusAuthCommand   command,
                                                           const DBusString *args);

static const DBusAuthStateData client_state_need_send_auth = {
  "NeedSendAuth", NULL
};
static const DBusAuthStateData client_state_waiting_for_data = {
  "WaitingForData", handle_client_state_waiting_for_data
};
static const DBusAuthStateData client_state_waiting_for_ok = {
  "WaitingForOK", handle_client_state_waiting_for_ok
};
static const DBusAuthStateData client_state_waiting_for_reject = {
  "WaitingForReject", handle_client_state_waiting_for_reject
};
  
static const DBusAuthStateData common_state_authenticated = {
  "Authenticated",  NULL
};

static const DBusAuthStateData common_state_need_disconnect = {
  "NeedDisconnect",  NULL
};

static const char auth_side_client[] = "client";
static const char auth_side_server[] = "server";
#define DBUS_AUTH_IS_SERVER(auth) ((auth)->side == auth_side_server)

#define DBUS_AUTH_IS_CLIENT(auth) ((auth)->side == auth_side_client)

#define DBUS_AUTH_CLIENT(auth)    ((DBusAuthClient*)(auth))

#define DBUS_AUTH_SERVER(auth)    ((DBusAuthServer*)(auth))

#define DBUS_AUTH_NAME(auth)      ((auth)->side)

static DBusAuth*
_dbus_auth_new (int size)
{
  DBusAuth *auth;
  
  auth = dbus_malloc0 (size);
  if (auth == NULL)
    return NULL;
  
  auth->refcount = 1;

  _dbus_credentials_clear (&auth->credentials);
  _dbus_credentials_clear (&auth->authorized_identity);
  _dbus_credentials_clear (&auth->desired_identity);
  
  auth->keyring = NULL;
  auth->cookie_id = -1;
  
  /* note that we don't use the max string length feature,
   * because you can't use that feature if you're going to
   * try to recover from out-of-memory (it creates
   * what looks like unrecoverable inability to alloc
   * more space in the string). But we do handle
   * overlong buffers in _dbus_auth_do_work().
   */
  
  if (!_dbus_string_init (&auth->incoming))
    goto enomem_0;

  if (!_dbus_string_init (&auth->outgoing))
    goto enomem_1;
    
  if (!_dbus_string_init (&auth->identity))
    goto enomem_2;

  if (!_dbus_string_init (&auth->context))
    goto enomem_3;

  if (!_dbus_string_init (&auth->challenge))
    goto enomem_4;

  /* default context if none is specified */
  if (!_dbus_string_append (&auth->context, "org_freedesktop_general"))
    goto enomem_5;
  
  return auth;

 enomem_5:
  _dbus_string_free (&auth->challenge);
 enomem_4:
  _dbus_string_free (&auth->context);
 enomem_3:
  _dbus_string_free (&auth->identity);
 enomem_2:
  _dbus_string_free (&auth->outgoing);
 enomem_1:
  _dbus_string_free (&auth->incoming);
 enomem_0:
  dbus_free (auth);
  return NULL;
}

static void
shutdown_mech (DBusAuth *auth)
{
  /* Cancel any auth */
  auth->already_asked_for_initial_response = FALSE;
  _dbus_string_set_length (&auth->identity, 0);

  _dbus_credentials_clear (&auth->authorized_identity);
  _dbus_credentials_clear (&auth->desired_identity);
  
  if (auth->mech != NULL)
    {
      _dbus_verbose ("%s: Shutting down mechanism %s\n",
                     DBUS_AUTH_NAME (auth), auth->mech->mechanism);
      
      if (DBUS_AUTH_IS_CLIENT (auth))
        (* auth->mech->client_shutdown_func) (auth);
      else
        (* auth->mech->server_shutdown_func) (auth);
      
      auth->mech = NULL;
    }
}

/* Returns TRUE but with an empty string hash if the
 * cookie_id isn't known. As with all this code
 * TRUE just means we had enough memory.
 */
static dbus_bool_t
sha1_compute_hash (DBusAuth         *auth,
                   int               cookie_id,
                   const DBusString *server_challenge,
                   const DBusString *client_challenge,
                   DBusString       *hash)
{
  DBusString cookie;
  DBusString to_hash;
  dbus_bool_t retval;
  
  _dbus_assert (auth->keyring != NULL);

  retval = FALSE;
  
  if (!_dbus_string_init (&cookie))
    return FALSE;

  if (!_dbus_keyring_get_hex_key (auth->keyring, cookie_id,
                                  &cookie))
    goto out_0;

  if (_dbus_string_get_length (&cookie) == 0)
    {
      retval = TRUE;
      goto out_0;
    }

  if (!_dbus_string_init (&to_hash))
    goto out_0;
  
  if (!_dbus_string_copy (server_challenge, 0,
                          &to_hash, _dbus_string_get_length (&to_hash)))
    goto out_1;

  if (!_dbus_string_append (&to_hash, ":"))
    goto out_1;
  
  if (!_dbus_string_copy (client_challenge, 0,
                          &to_hash, _dbus_string_get_length (&to_hash)))
    goto out_1;

  if (!_dbus_string_append (&to_hash, ":"))
    goto out_1;

  if (!_dbus_string_copy (&cookie, 0,
                          &to_hash, _dbus_string_get_length (&to_hash)))
    goto out_1;

  if (!_dbus_sha_compute (&to_hash, hash))
    goto out_1;
  
  retval = TRUE;

 out_1:
  _dbus_string_zero (&to_hash);
  _dbus_string_free (&to_hash);
 out_0:
  _dbus_string_zero (&cookie);
  _dbus_string_free (&cookie);
  return retval;
}

#define N_CHALLENGE_BYTES (128/8)

static dbus_bool_t
sha1_handle_first_client_response (DBusAuth         *auth,
                                   const DBusString *data)
{
  /* We haven't sent a challenge yet, we're expecting a desired
   * username from the client.
   */
  DBusString tmp;
  DBusString tmp2;
  dbus_bool_t retval;
  DBusError error;
  
  retval = FALSE;

  _dbus_string_set_length (&auth->challenge, 0);
  
  if (_dbus_string_get_length (data) > 0)
    {
      if (_dbus_string_get_length (&auth->identity) > 0)
        {
          /* Tried to send two auth identities, wtf */
          _dbus_verbose ("%s: client tried to send auth identity, but we already have one\n",
                         DBUS_AUTH_NAME (auth));
          return send_rejected (auth);
        }
      else
        {
          /* this is our auth identity */
          if (!_dbus_string_copy (data, 0, &auth->identity, 0))
            return FALSE;
        }
    }
      
  if (!_dbus_credentials_from_username (data, &auth->desired_identity))
    {
      _dbus_verbose ("%s: Did not get a valid username from client\n",
                     DBUS_AUTH_NAME (auth));
      return send_rejected (auth);
    }
      
  if (!_dbus_string_init (&tmp))
    return FALSE;

  if (!_dbus_string_init (&tmp2))
    {
      _dbus_string_free (&tmp);
      return FALSE;
    }

  /* we cache the keyring for speed, so here we drop it if it's the
   * wrong one. FIXME caching the keyring here is useless since we use
   * a different DBusAuth for every connection.
   */
  if (auth->keyring &&
      !_dbus_keyring_is_for_user (auth->keyring,
                                  data))
    {
      _dbus_keyring_unref (auth->keyring);
      auth->keyring = NULL;
    }
  
  if (auth->keyring == NULL)
    {
      dbus_error_init (&error);
      auth->keyring = _dbus_keyring_new_homedir (data,
                                                 &auth->context,
                                                 &error);

      if (auth->keyring == NULL)
        {
          if (dbus_error_has_name (&error,
                                   DBUS_ERROR_NO_MEMORY))
            {
              dbus_error_free (&error);
              goto out;
            }
          else
            {
              _DBUS_ASSERT_ERROR_IS_SET (&error);
              _dbus_verbose ("%s: Error loading keyring: %s\n",
                             DBUS_AUTH_NAME (auth), error.message);
              if (send_rejected (auth))
                retval = TRUE; /* retval is only about mem */
              dbus_error_free (&error);
              goto out;
            }
        }
      else
        {
          _dbus_assert (!dbus_error_is_set (&error));
        }
    }

  _dbus_assert (auth->keyring != NULL);

  dbus_error_init (&error);
  auth->cookie_id = _dbus_keyring_get_best_key (auth->keyring, &error);
  if (auth->cookie_id < 0)
    {
      _DBUS_ASSERT_ERROR_IS_SET (&error);
      _dbus_verbose ("%s: Could not get a cookie ID to send to client: %s\n",
                     DBUS_AUTH_NAME (auth), error.message);
      if (send_rejected (auth))
        retval = TRUE;
      dbus_error_free (&error);
      goto out;
    }
  else
    {
      _dbus_assert (!dbus_error_is_set (&error));
    }

  if (!_dbus_string_copy (&auth->context, 0,
                          &tmp2, _dbus_string_get_length (&tmp2)))
    goto out;

  if (!_dbus_string_append (&tmp2, " "))
    goto out;

  if (!_dbus_string_append_int (&tmp2, auth->cookie_id))
    goto out;

  if (!_dbus_string_append (&tmp2, " "))
    goto out;  
  
  if (!_dbus_generate_random_bytes (&tmp, N_CHALLENGE_BYTES))
    goto out;

  _dbus_string_set_length (&auth->challenge, 0);
  if (!_dbus_string_hex_encode (&tmp, 0, &auth->challenge, 0))
    goto out;
  
  if (!_dbus_string_hex_encode (&tmp, 0, &tmp2,
                                _dbus_string_get_length (&tmp2)))
    goto out;

  if (!send_data (auth, &tmp2))
    goto out;
      
  goto_state (auth, &server_state_waiting_for_data);
  retval = TRUE;
  
 out:
  _dbus_string_zero (&tmp);
  _dbus_string_free (&tmp);
  _dbus_string_zero (&tmp2);
  _dbus_string_free (&tmp2);

  return retval;
}

static dbus_bool_t
sha1_handle_second_client_response (DBusAuth         *auth,
                                    const DBusString *data)
{
  /* We are expecting a response which is the hex-encoded client
   * challenge, space, then SHA-1 hash of the concatenation of our
   * challenge, ":", client challenge, ":", secret key, all
   * hex-encoded.
   */
  int i;
  DBusString client_challenge;
  DBusString client_hash;
  dbus_bool_t retval;
  DBusString correct_hash;
  
  retval = FALSE;
  
  if (!_dbus_string_find_blank (data, 0, &i))
    {
      _dbus_verbose ("%s: no space separator in client response\n",
                     DBUS_AUTH_NAME (auth));
      return send_rejected (auth);
    }
  
  if (!_dbus_string_init (&client_challenge))
    goto out_0;

  if (!_dbus_string_init (&client_hash))
    goto out_1;  

  if (!_dbus_string_copy_len (data, 0, i, &client_challenge,
                              0))
    goto out_2;

  _dbus_string_skip_blank (data, i, &i);
  
  if (!_dbus_string_copy_len (data, i,
                              _dbus_string_get_length (data) - i,
                              &client_hash,
                              0))
    goto out_2;

  if (_dbus_string_get_length (&client_challenge) == 0 ||
      _dbus_string_get_length (&client_hash) == 0)
    {
      _dbus_verbose ("%s: zero-length client challenge or hash\n",
                     DBUS_AUTH_NAME (auth));
      if (send_rejected (auth))
        retval = TRUE;
      goto out_2;
    }

  if (!_dbus_string_init (&correct_hash))
    goto out_2;

  if (!sha1_compute_hash (auth, auth->cookie_id,
                          &auth->challenge, 
                          &client_challenge,
                          &correct_hash))
    goto out_3;

  /* if cookie_id was invalid, then we get an empty hash */
  if (_dbus_string_get_length (&correct_hash) == 0)
    {
      if (send_rejected (auth))
        retval = TRUE;
      goto out_3;
    }
  
  if (!_dbus_string_equal (&client_hash, &correct_hash))
    {
      if (send_rejected (auth))
        retval = TRUE;
      goto out_3;
    }
      
  if (!send_ok (auth))
    goto out_3;

  _dbus_verbose ("%s: authenticated client with UID "DBUS_UID_FORMAT" using DBUS_COOKIE_SHA1\n",
                 DBUS_AUTH_NAME (auth), auth->desired_identity.uid);
  
  auth->authorized_identity = auth->desired_identity;
  retval = TRUE;
  
 out_3:
  _dbus_string_zero (&correct_hash);
  _dbus_string_free (&correct_hash);
 out_2:
  _dbus_string_zero (&client_hash);
  _dbus_string_free (&client_hash);
 out_1:
  _dbus_string_free (&client_challenge);
 out_0:
  return retval;
}

static dbus_bool_t
handle_server_data_cookie_sha1_mech (DBusAuth         *auth,
                                     const DBusString *data)
{
  if (auth->cookie_id < 0)
    return sha1_handle_first_client_response (auth, data);
  else
    return sha1_handle_second_client_response (auth, data);
}

static void
handle_server_shutdown_cookie_sha1_mech (DBusAuth *auth)
{
  auth->cookie_id = -1;  
  _dbus_string_set_length (&auth->challenge, 0);
}

static dbus_bool_t
handle_client_initial_response_cookie_sha1_mech (DBusAuth   *auth,
                                                 DBusString *response)
{
  const DBusString *username;
  dbus_bool_t retval;

  retval = FALSE;

  if (!_dbus_username_from_current_process (&username))
    goto out_0;

  if (!_dbus_string_hex_encode (username, 0,
                                response,
                                _dbus_string_get_length (response)))
    goto out_0;

  retval = TRUE;
  
 out_0:
  return retval;
}

static dbus_bool_t
handle_client_data_cookie_sha1_mech (DBusAuth         *auth,
                                     const DBusString *data)
{
  /* The data we get from the server should be the cookie context
   * name, the cookie ID, and the server challenge, separated by
   * spaces. We send back our challenge string and the correct hash.
   */
  dbus_bool_t retval;
  DBusString context;
  DBusString cookie_id_str;
  DBusString server_challenge;
  DBusString client_challenge;
  DBusString correct_hash;
  DBusString tmp;
  int i, j;
  long val;
  
  retval = FALSE;                 
  
  if (!_dbus_string_find_blank (data, 0, &i))
    {
      if (send_error (auth,
                      "Server did not send context/ID/challenge properly"))
        retval = TRUE;
      goto out_0;
    }

  if (!_dbus_string_init (&context))
    goto out_0;

  if (!_dbus_string_copy_len (data, 0, i,
                              &context, 0))
    goto out_1;
  
  _dbus_string_skip_blank (data, i, &i);
  if (!_dbus_string_find_blank (data, i, &j))
    {
      if (send_error (auth,
                      "Server did not send context/ID/challenge properly"))
        retval = TRUE;
      goto out_1;
    }

  if (!_dbus_string_init (&cookie_id_str))
    goto out_1;
  
  if (!_dbus_string_copy_len (data, i, j - i,
                              &cookie_id_str, 0))
    goto out_2;  

  if (!_dbus_string_init (&server_challenge))
    goto out_2;

  i = j;
  _dbus_string_skip_blank (data, i, &i);
  j = _dbus_string_get_length (data);

  if (!_dbus_string_copy_len (data, i, j - i,
                              &server_challenge, 0))
    goto out_3;

  if (!_dbus_keyring_validate_context (&context))
    {
      if (send_error (auth, "Server sent invalid cookie context"))
        retval = TRUE;
      goto out_3;
    }

  if (!_dbus_string_parse_int (&cookie_id_str, 0, &val, NULL))
    {
      if (send_error (auth, "Could not parse cookie ID as an integer"))
        retval = TRUE;
      goto out_3;
    }

  if (_dbus_string_get_length (&server_challenge) == 0)
    {
      if (send_error (auth, "Empty server challenge string"))
        retval = TRUE;
      goto out_3;
    }

  if (auth->keyring == NULL)
    {
      DBusError error;

      dbus_error_init (&error);
      auth->keyring = _dbus_keyring_new_homedir (NULL,
                                                 &context,
                                                 &error);

      if (auth->keyring == NULL)
        {
          if (dbus_error_has_name (&error,
                                   DBUS_ERROR_NO_MEMORY))
            {
              dbus_error_free (&error);
              goto out_3;
            }
          else
            {
              _DBUS_ASSERT_ERROR_IS_SET (&error);

              _dbus_verbose ("%s: Error loading keyring: %s\n",
                             DBUS_AUTH_NAME (auth), error.message);
              
              if (send_error (auth, "Could not load cookie file"))
                retval = TRUE; /* retval is only about mem */
              
              dbus_error_free (&error);
              goto out_3;
            }
        }
      else
        {
          _dbus_assert (!dbus_error_is_set (&error));
        }
    }
  
  _dbus_assert (auth->keyring != NULL);
  
  if (!_dbus_string_init (&tmp))
    goto out_3;
  
  if (!_dbus_generate_random_bytes (&tmp, N_CHALLENGE_BYTES))
    goto out_4;

  if (!_dbus_string_init (&client_challenge))
    goto out_4;

  if (!_dbus_string_hex_encode (&tmp, 0, &client_challenge, 0))
    goto out_5;

  if (!_dbus_string_init (&correct_hash))
    goto out_5;
  
  if (!sha1_compute_hash (auth, val,
                          &server_challenge,
                          &client_challenge,
                          &correct_hash))
    goto out_6;

  if (_dbus_string_get_length (&correct_hash) == 0)
    {
      /* couldn't find the cookie ID or something */
      if (send_error (auth, "Don't have the requested cookie ID"))
        retval = TRUE;
      goto out_6;
    }
  
  _dbus_string_set_length (&tmp, 0);
  
  if (!_dbus_string_copy (&client_challenge, 0, &tmp,
                          _dbus_string_get_length (&tmp)))
    goto out_6;

  if (!_dbus_string_append (&tmp, " "))
    goto out_6;

  if (!_dbus_string_copy (&correct_hash, 0, &tmp,
                          _dbus_string_get_length (&tmp)))
    goto out_6;

  if (!send_data (auth, &tmp))
    goto out_6;

  retval = TRUE;

 out_6:
  _dbus_string_zero (&correct_hash);
  _dbus_string_free (&correct_hash);
 out_5:
  _dbus_string_free (&client_challenge);
 out_4:
  _dbus_string_zero (&tmp);
  _dbus_string_free (&tmp);
 out_3:
  _dbus_string_free (&server_challenge);
 out_2:
  _dbus_string_free (&cookie_id_str);
 out_1:
  _dbus_string_free (&context);
 out_0:
  return retval;
}

static void
handle_client_shutdown_cookie_sha1_mech (DBusAuth *auth)
{
  auth->cookie_id = -1;  
  _dbus_string_set_length (&auth->challenge, 0);
}

static dbus_bool_t
handle_server_data_external_mech (DBusAuth         *auth,
                                  const DBusString *data)
{
  if (auth->credentials.uid == DBUS_UID_UNSET)
    {
      _dbus_verbose ("%s: no credentials, mechanism EXTERNAL can't authenticate\n",
                     DBUS_AUTH_NAME (auth));
      return send_rejected (auth);
    }
  
  if (_dbus_string_get_length (data) > 0)
    {
      if (_dbus_string_get_length (&auth->identity) > 0)
        {
          /* Tried to send two auth identities, wtf */
          _dbus_verbose ("%s: client tried to send auth identity, but we already have one\n",
                         DBUS_AUTH_NAME (auth));
          return send_rejected (auth);
        }
      else
        {
          /* this is our auth identity */
          if (!_dbus_string_copy (data, 0, &auth->identity, 0))
            return FALSE;
        }
    }

  /* Poke client for an auth identity, if none given */
  if (_dbus_string_get_length (&auth->identity) == 0 &&
      !auth->already_asked_for_initial_response)
    {
      if (send_data (auth, NULL))
        {
          _dbus_verbose ("%s: sending empty challenge asking client for auth identity\n",
                         DBUS_AUTH_NAME (auth));
          auth->already_asked_for_initial_response = TRUE;
          return TRUE;
        }
      else
        return FALSE;
    }

  _dbus_credentials_clear (&auth->desired_identity);
  
  /* If auth->identity is still empty here, then client
   * responded with an empty string after we poked it for
   * an initial response. This means to try to auth the
   * identity provided in the credentials.
   */
  if (_dbus_string_get_length (&auth->identity) == 0)
    {
      auth->desired_identity.uid = auth->credentials.uid;
    }
  else
    {
      if (!_dbus_parse_uid (&auth->identity,
                            &auth->desired_identity.uid))
        {
          _dbus_verbose ("%s: could not get credentials from uid string\n",
                         DBUS_AUTH_NAME (auth));
          return send_rejected (auth);
        }
    }

  if (auth->desired_identity.uid == DBUS_UID_UNSET)
    {
      _dbus_verbose ("%s: desired user %s is no good\n",
                     DBUS_AUTH_NAME (auth),
                     _dbus_string_get_const_data (&auth->identity));
      return send_rejected (auth);
    }
  
  if (_dbus_credentials_match (&auth->desired_identity,
                               &auth->credentials))
    {
      /* client has authenticated */      
      if (!send_ok (auth))
        return FALSE;

      _dbus_verbose ("%s: authenticated client with UID "DBUS_UID_FORMAT
                     " matching socket credentials UID "DBUS_UID_FORMAT"\n",
                     DBUS_AUTH_NAME (auth),
                     auth->desired_identity.uid,
                     auth->credentials.uid);

      auth->authorized_identity.pid = auth->credentials.pid;
      auth->authorized_identity.uid = auth->desired_identity.uid;
      return TRUE;
    }
  else
    {
      _dbus_verbose ("%s: credentials uid="DBUS_UID_FORMAT
                     " gid="DBUS_GID_FORMAT
                     " do not allow uid="DBUS_UID_FORMAT
                     " gid="DBUS_GID_FORMAT"\n",
                     DBUS_AUTH_NAME (auth),
                     auth->credentials.uid, auth->credentials.gid,
                     auth->desired_identity.uid, auth->desired_identity.gid);
      return send_rejected (auth);
    }
}

static void
handle_server_shutdown_external_mech (DBusAuth *auth)
{

}

static dbus_bool_t
handle_client_initial_response_external_mech (DBusAuth         *auth,
                                              DBusString       *response)
{
  /* We always append our UID as an initial response, so the server
   * doesn't have to send back an empty challenge to check whether we
   * want to specify an identity. i.e. this avoids a round trip that
   * the spec for the EXTERNAL mechanism otherwise requires.
   */
  DBusString plaintext;

  if (!_dbus_string_init (&plaintext))
    return FALSE;
  
  if (!_dbus_string_append_uint (&plaintext,
                                 _dbus_getuid ()))
    goto failed;

  if (!_dbus_string_hex_encode (&plaintext, 0,
                                response,
                                _dbus_string_get_length (response)))
    goto failed;

  _dbus_string_free (&plaintext);
  
  return TRUE;

 failed:
  _dbus_string_free (&plaintext);
  return FALSE;  
}

static dbus_bool_t
handle_client_data_external_mech (DBusAuth         *auth,
                                  const DBusString *data)
{
  
  return TRUE;
}

static void
handle_client_shutdown_external_mech (DBusAuth *auth)
{

}

/* Put mechanisms here in order of preference.
 * What I eventually want to have is:
 *
 *  - a mechanism that checks UNIX domain socket credentials
 *  - a simple magic cookie mechanism like X11 or ICE
 *  - mechanisms that chain to Cyrus SASL, so we can use anything it
 *    offers such as Kerberos, X509, whatever.
 * 
 */
static const DBusAuthMechanismHandler
all_mechanisms[] = {
  { "EXTERNAL",
    handle_server_data_external_mech,
    NULL, NULL,
    handle_server_shutdown_external_mech,
    handle_client_initial_response_external_mech,
    handle_client_data_external_mech,
    NULL, NULL,
    handle_client_shutdown_external_mech },
  { "DBUS_COOKIE_SHA1",
    handle_server_data_cookie_sha1_mech,
    NULL, NULL,
    handle_server_shutdown_cookie_sha1_mech,
    handle_client_initial_response_cookie_sha1_mech,
    handle_client_data_cookie_sha1_mech,
    NULL, NULL,
    handle_client_shutdown_cookie_sha1_mech },
  { NULL, NULL }
};

static const DBusAuthMechanismHandler*
find_mech (const DBusString  *name,
           char             **allowed_mechs)
{
  int i;
  
  if (allowed_mechs != NULL &&
      !_dbus_string_array_contains ((const char**) allowed_mechs,
                                    _dbus_string_get_const_data (name)))
    return NULL;
  
  i = 0;
  while (all_mechanisms[i].mechanism != NULL)
    {      
      if (_dbus_string_equal_c_str (name,
                                    all_mechanisms[i].mechanism))

        return &all_mechanisms[i];
      
      ++i;
    }
  
  return NULL;
}

static dbus_bool_t
send_auth (DBusAuth *auth, const DBusAuthMechanismHandler *mech)
{
  DBusString auth_command;

  if (!_dbus_string_init (&auth_command))
    return FALSE;
      
  if (!_dbus_string_append (&auth_command,
                            "AUTH "))
    {
      _dbus_string_free (&auth_command);
      return FALSE;
    }  
  
  if (!_dbus_string_append (&auth_command,
                            mech->mechanism))
    {
      _dbus_string_free (&auth_command);
      return FALSE;
    }

  if (mech->client_initial_response_func != NULL)
    {
      if (!_dbus_string_append (&auth_command, " "))
        {
          _dbus_string_free (&auth_command);
          return FALSE;
        }
      
      if (!(* mech->client_initial_response_func) (auth, &auth_command))
        {
          _dbus_string_free (&auth_command);
          return FALSE;
        }
    }
  
  if (!_dbus_string_append (&auth_command,
                            "\r\n"))
    {
      _dbus_string_free (&auth_command);
      return FALSE;
    }

  if (!_dbus_string_copy (&auth_command, 0,
                          &auth->outgoing,
                          _dbus_string_get_length (&auth->outgoing)))
    {
      _dbus_string_free (&auth_command);
      return FALSE;
    }

  _dbus_string_free (&auth_command);
  shutdown_mech (auth);
  auth->mech = mech;      
  goto_state (auth, &client_state_waiting_for_data);

  return TRUE;
}

static dbus_bool_t
send_data (DBusAuth *auth, DBusString *data)
{
  int old_len;

  if (data == NULL || _dbus_string_get_length (data) == 0)
    return _dbus_string_append (&auth->outgoing, "DATA\r\n");
  else
    {
      old_len = _dbus_string_get_length (&auth->outgoing);
      if (!_dbus_string_append (&auth->outgoing, "DATA "))
        goto out;

      if (!_dbus_string_hex_encode (data, 0, &auth->outgoing,
                                    _dbus_string_get_length (&auth->outgoing)))
        goto out;

      if (!_dbus_string_append (&auth->outgoing, "\r\n"))
        goto out;

      return TRUE;

    out:
      _dbus_string_set_length (&auth->outgoing, old_len);

      return FALSE;
    }
}

static dbus_bool_t
send_rejected (DBusAuth *auth)
{
  DBusString command;
  DBusAuthServer *server_auth;
  int i;
  
  if (!_dbus_string_init (&command))
    return FALSE;
  
  if (!_dbus_string_append (&command,
                            "REJECTED"))
    goto nomem;

  i = 0;
  while (all_mechanisms[i].mechanism != NULL)
    {
      if (!_dbus_string_append (&command,
                                " "))
        goto nomem;

      if (!_dbus_string_append (&command,
                                all_mechanisms[i].mechanism))
        goto nomem;
      
      ++i;
    }
  
  if (!_dbus_string_append (&command, "\r\n"))
    goto nomem;

  if (!_dbus_string_copy (&command, 0, &auth->outgoing,
                          _dbus_string_get_length (&auth->outgoing)))
    goto nomem;

  shutdown_mech (auth);
  
  _dbus_assert (DBUS_AUTH_IS_SERVER (auth));
  server_auth = DBUS_AUTH_SERVER (auth);
  server_auth->failures += 1;

  if (server_auth->failures >= server_auth->max_failures)