** Searches for the user ID matching the given name and password.
** On success it returns a positive value. On error it returns 0.
** On serious (DB-level) error it will probably exit.
**
** zPassword may be either the plain-text form or the encrypted
** form of the user's password.
*/
int login_search_uid(char const *zUsername, char const *zPasswd){
  char * zSha1Pw = sha1_shared_secret(zPasswd, zUsername, 0);
  int const uid =
      db_int(0,
             "SELECT uid FROM user"
             " WHERE login=%Q"
             "   AND length(cap)>0 AND length(pw)>0"
             "   AND login NOT IN ('anonymous','nobody','developer','reader')"
             "   AND (pw=%Q OR (length(pw)<>40 AND pw=%Q))",

** Generates a login cookie value for a non-anonymous user.
**
** The zHash parameter must be a random value which must be
** subsequently stored in user.cookie for later validation.
**
** The returned memory should be free()d after use.
*/
char * login_gen_user_cookie_value(char const *zUsername, char const * zHash){
  char * zProjCode = db_get("project-code",NULL);
  char *zCode = abbreviated_project_code(zProjCode);
  free(zProjCode);
  assert((zUsername && *zUsername) && "Invalid user data.");
  return mprintf("%s/%z/%s", zHash, zCode, zUsername);
}

/*
** Generates a login cookie for NON-ANONYMOUS users.  Note that this
** function "could" figure out the uid by itself but it currently
** doesn't because the code which calls this already has the uid.
**
** This function also updates the user.cookie, user.ipaddr,
** and user.cexpire fields for the given user.
**
** If zDest is not NULL then the generated cookie is copied to
** *zDdest and ownership is transfered to the caller (who should
** eventually pass it to free()).
*/
void login_set_user_cookie(
  char const * zUsername, /* User's name */
  int uid,                /* User's ID */
  char ** zDest           /* Optional: store generated cookie value. */
){
  const char *zCookieName = login_cookie_name();
  const char *zExpire = db_get("cookie-expire","8766");
  int expires = atoi(zExpire)*3600;
  char *zHash;
  char *zCookie;
  char const *zIpAddr = PD("REMOTE_ADDR","nil"); /* IP address of user */
  char *zRemoteAddr = ipPrefix(zIpAddr);         /* Abbreviated IP address */

  assert((zUsername && *zUsername) && (uid > 0) && "Invalid user data.");
  zHash = db_text(0,
      "SELECT cookie FROM user"
      " WHERE uid=%d"
      "   AND ipaddr=%Q"

**
** If either zIpAddr or zRemoteAddr are NULL then REMOTE_ADDR
** is used.
**
** If zCookieDest is not NULL then the generated cookie is assigned to
** *zCookieDest and the caller must eventually free() it.
*/
void login_set_anon_cookie(char const * zIpAddr, char ** zCookieDest ){
  char const *zNow;            /* Current time (julian day number) */
  char *zCookie;               /* The login cookie */
  char const *zCookieName;     /* Name of the login cookie */
  Blob b;                      /* Blob used during cookie construction */
  char * zRemoteAddr;     /* Abbreviated IP address */
  if(!zIpAddr){
    zIpAddr = PD("REMOTE_ADDR","nil");
  }
  zRemoteAddr = ipPrefix(zIpAddr);
  zCookieName = login_cookie_name();
  zNow = db_text("0", "SELECT julianday('now')");
  assert( zCookieName && zRemoteAddr && zIpAddr && zNow );

**
** This is a no-op if g.userUid is 0.
*/
void login_clear_login_data(){
  if(!g.userUid){
    return;
  }else{
    char const * cookie = login_cookie_name();
    /* To logout, change the cookie value to an empty string */
    cgi_set_cookie(cookie, "",
                   login_cookie_path(), -86400);
    db_multi_exec("UPDATE user SET cookie=NULL, ipaddr=NULL, "
                  "  cexpire=0 WHERE uid=%d"
                  "  AND login NOT IN ('anonymous','nobody',"
                  "  'developer','reader')", g.userUid);

  @ the login to take.</p>
  if( db_get_boolean("self-register", 0) ){
    @ <p>If you do not have an account, you can
    @ <a href="%s(g.zTop)/register?g=%T(P("G"))">create one</a>.
  }
  if( zAnonPw ){
    unsigned int uSeed = captcha_seed();
    char const *zDecoded = captcha_decode(uSeed);
    int bAutoCaptcha = db_get_boolean("auto-captcha", 0);
    char *zCaptcha = captcha_render(zDecoded);

    @ <p><input type="hidden" name="cs" value="%u(uSeed)" />
    @ Visitors may enter <b>anonymous</b> as the user-ID with
    @ the 8-character hexadecimal password shown below:</p>
    @ <div class="captcha"><table class="captcha"><tr><td><pre>

**
** Generate the register page.
**
*/
void register_page(void){
  const char *zUsername, *zPasswd, *zConfirm, *zContact, *zCS, *zPw, *zCap;
  unsigned int uSeed;
  char const *zDecoded;
  char *zCaptcha;
  if( !db_get_boolean("self-register", 0) ){
    style_header("Registration not possible");
    @ <p>This project does not allow user self-registration. Please contact the
    @ project administrator to obtain an account.</p>
    style_footer();
    return;