code: // Licensed to the Software Freedom Conservancy (SFC) under one
  // or more contributor license agreements.  See the NOTICE file
  // distributed with this work for additional information
  // regarding copyright ownership.  The SFC licenses this file
  // to you under the Apache License, Version 2.0 (the
  // "License"); you may not use this file except in compliance
  // with the License.  You may obtain a copy of the License at
  //
  //   http://www.apache.org/licenses/LICENSE-2.0
  //
  // Unless required by applicable law or agreed to in writing,
  // software distributed under the License is distributed on an
  // "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
  // KIND, either express or implied.  See the License for the
  // specific language governing permissions and limitations
  // under the License.
  
  package org.openqa.selenium.grid.security;
  
  import static java.net.HttpURLConnection.HTTP_UNAUTHORIZED;
  import static org.openqa.selenium.grid.security.AddSecretFilter.HEADER_NAME;
  import static org.openqa.selenium.json.Json.JSON_UTF_8;
  
  import com.google.common.collect.ImmutableMap;
  import java.util.Collections;
  import java.util.logging.Logger;
  import org.openqa.selenium.internal.Require;
  import org.openqa.selenium.remote.http.Contents;
  import org.openqa.selenium.remote.http.Filter;
  import org.openqa.selenium.remote.http.HttpHandler;
  import org.openqa.selenium.remote.http.HttpRequest;
  import org.openqa.selenium.remote.http.HttpResponse;
  
  public class RequiresSecretFilter implements Filter {
  
    private static final Logger LOG = Logger.getLogger(RequiresSecretFilter.class.getName());
    private final Secret secret;
  
    public RequiresSecretFilter(Secret secret) {
      this.secret = Require.nonNull("Secret", secret);
    }
  
    @Override
    public HttpHandler apply(HttpHandler httpHandler) {
      Require.nonNull("HTTP handler", httpHandler);
  
      return req -> {
        if (!isSecretMatch(secret, req)) {
          return new HttpResponse()
              .setStatus(HTTP_UNAUTHORIZED)
              .addHeader("Content-Type", JSON_UTF_8)
              .setContent(
                  Contents.asJson(
                      Collections.singletonMap(
                          "value",
                          ImmutableMap.of(
                              "error", "unknown error",
                              "message", "Unauthorized access attempted to ",
                              "stacktrace", ""))));
        }
  
        return httpHandler.execute(req);
      };
    }
  
    private boolean isSecretMatch(Secret secret, HttpRequest request) {
      String header = request.getHeader(HEADER_NAME);
      if (header == null) {
        if (secret != null) {
          LOG.warning("Unexpectedly received registration secret to " + request);
          return false;
        }
        return true;
      }
  
      Secret requestSecret = new Secret(header);
  
      if (!secret.matches(requestSecret)) {
        LOG.warning("Unauthorized access attempted to " + request);
        return false;
      }
  
      return true;
    }
  }
  