In OpenERP first create the users and then users is retrieve an active resource of model res_users with the specified login. When users login in web page then verify all the rights and authentication. If users rights and authentication both is fine then users is login successfully in web pages.
Use this function given below

def createuser(self, cr, uid, conf, login, ldap_entry,
                           context=None):
   
        user_id = False
        login = tools.ustr(login)
        cr.execute("SELECT id, active FROM res_users WHERE login=%s", (login,))
        res = cr.fetchone()
        if res:
            if res[1]:
                user_id = res[0]
        elif conf['create_user']:
            logger = logging.getLogger('orm.ldap')
            logger.debug("Creating new OpenERP user \"%s\" from LDAP" % login)
            user_obj = self.pool.get('res.users')
            values = self.map_ldap_attributes(cr, uid, conf, login, ldap_entry)
            if conf['user']:
                user_id = user_obj.copy(cr, SUPERUSER_ID, conf['user'],
                                        default={'active': True})
                user_obj.write(cr, SUPERUSER_ID, user_id, values)
            else:
                user_id = user_obj.create(cr, SUPERUSER_ID, values)
        return user_id