_authenticate

# File lib/webrick/httpauth/digestauth.rb, line 102
      def _authenticate(req, res)
        unless digest_credentials = check_scheme(req)
          return false
        end

        auth_req = split_param_value(digest_credentials)
        if auth_req['qop'] == "auth" || auth_req['qop'] == "auth-int"
          req_params = MustParams + MustParamsAuth
        else
          req_params = MustParams
        end
        req_params.each{|key|
          unless auth_req.has_key?(key)
            error('%s: parameter missing. "%s"', auth_req['username'], key)
            raise HTTPStatus::BadRequest
          end
        }

        if !check_uri(req, auth_req)
          raise HTTPStatus::BadRequest  
        end

        if auth_req['realm'] != @realm  
          error('%s: realm unmatch. "%s" for "%s"',
                auth_req['username'], auth_req['realm'], @realm)
          return false
        end

        auth_req['algorithm'] ||= 'MD5' 
        if auth_req['algorithm'] != @algorithm &&
           (@opera_hack && auth_req['algorithm'] != @algorithm.upcase)
          error('%s: algorithm unmatch. "%s" for "%s"',
                auth_req['username'], auth_req['algorithm'], @algorithm)
          return false
        end

        if (@qop.nil? && auth_req.has_key?('qop')) ||
           (@qop && (! @qop.member?(auth_req['qop'])))
          error('%s: the qop is not allowed. "%s"',
                auth_req['username'], auth_req['qop'])
          return false
        end

        password = @userdb.get_passwd(@realm, auth_req['username'], @reload_db)
        unless password
          error('%s: the user is not allowd.', auth_req['username'])
          return false
        end

        nonce_is_invalid = false
        if @use_opaque
          info("@opaque = %s", @opaque.inspect) if $DEBUG
          if !(opaque = auth_req['opaque'])
            error('%s: opaque is not given.', auth_req['username'])
            nonce_is_invalid = true
          elsif !(opaque_struct = @opaques[opaque])
            error('%s: invalid opaque is given.', auth_req['username'])
            nonce_is_invalid = true
          elsif !check_opaque(opaque_struct, req, auth_req)
            @opaques.delete(auth_req['opaque'])
            nonce_is_invalid = true
          end
        elsif !check_nonce(req, auth_req)
          nonce_is_invalid = true
        end

        if /-sess$/ =~ auth_req['algorithm'] ||
           (@opera_hack && /-SESS$/ =~ auth_req['algorithm'])
          ha1 = hexdigest(password, auth_req['nonce'], auth_req['cnonce'])
        else
          ha1 = password
        end

        if auth_req['qop'] == "auth" || auth_req['qop'] == nil
          ha2 = hexdigest(req.request_method, auth_req['uri'])
          ha2_res = hexdigest("", auth_req['uri'])
        elsif auth_req['qop'] == "auth-int"
          ha2 = hexdigest(req.request_method, auth_req['uri'],
                          hexdigest(req.body))
          ha2_res = hexdigest("", auth_req['uri'], hexdigest(res.body))
        end

        if auth_req['qop'] == "auth" || auth_req['qop'] == "auth-int"
          param2 = ['nonce', 'nc', 'cnonce', 'qop'].map{|key|
            auth_req[key]
          }.join(':')
          digest     = hexdigest(ha1, param2, ha2)
          digest_res = hexdigest(ha1, param2, ha2_res)
        else
          digest     = hexdigest(ha1, auth_req['nonce'], ha2)
          digest_res = hexdigest(ha1, auth_req['nonce'], ha2_res)
        end

        if digest != auth_req['response']
          error("%s: digest unmatch.", auth_req['username'])
          return false
        elsif nonce_is_invalid
          error('%s: digest is valid, but nonce is not valid.',
                auth_req['username'])
          return :nonce_is_stale
        elsif @use_auth_info_header
          auth_info = {
            'nextnonce' => generate_next_nonce(req),
            'rspauth'   => digest_res
          }
          if @use_opaque
            opaque_struct.time  = req.request_time
            opaque_struct.nonce = auth_info['nextnonce']
            opaque_struct.nc    = "%08x" % (auth_req['nc'].hex + 1)
          end
          if auth_req['qop'] == "auth" || auth_req['qop'] == "auth-int"
            ['qop','cnonce','nc'].each{|key|
              auth_info[key] = auth_req[key]
            }
          end
          res[@resp_info_field] = auth_info.keys.map{|key|
            if key == 'nc'
              key + '=' + auth_info[key]
            else
              key + "=" + HTTPUtils::quote(auth_info[key])
            end
          }.join(', ')
        end
        info('%s: authentication scceeded.', auth_req['username'])
        req.user = auth_req['username']
        return true
      end