* They don't specify whether a specific proxy server should be used or how to authenticate with that proxy server.

They're also concrete: each URL identifies a specific path (like `/square/okhttp`) and query (like `?q=sharks&lang=en`). Each webserver hosts many URLs.

    def make_not_authenticated_error(self) -> HTTPException:
        """
        The OAuth 2 specification doesn't define the challenge that should be used,
        because a `Bearer` token is not really the only option to authenticate.

        But declaring any other authentication challenge would be application-specific
        as it's not defined in the specification.

        }
        try {
            // set some System properties
            final SpnegoFilterConfig config = SpnegoFilterConfig.getInstance(new SpnegoConfig());

            // pre-authenticate
            authenticator = new org.codelibs.spnego.SpnegoAuthenticator(config);

            fessConfig.setSystemPropertyAsBoolean(SPNEGO_INITIALIZED, true);
            fessConfig.storeSystemProperties();

  /** The HTTP {@code P3P} header field name. Limited browser support. */
  public static final String P3P = "P3P";

  /** The HTTP {@code Proxy-Authenticate} header field name. */
  public static final String PROXY_AUTHENTICATE = "Proxy-Authenticate";

  /** The HTTP {@code Refresh} header field name. Non-standard header supported by most browsers. */
  public static final String REFRESH = "Refresh";

  /**

authentication, you don't need to use `mc` to generate prometheus config. You can skip reading further and move to 3.2 section.

The Prometheus endpoint in MinIO requires authentication by default. Prometheus supports a bearer token approach to authenticate prometheus scrape requests, override the default Prometheus config with the one generated using mc. To generate a Prometheus config for an alias, use [mc](https://docs.min.io/community/minio-object-store/reference/minio-mc.html#quickstart) as follows...

                }
            }
            String authHeader;
            if (response == HTTP_UNAUTHORIZED) {
                authHeader = "WWW-Authenticate";
                this.authProperty = "Authorization";
            } else {
                authHeader = "Proxy-Authenticate";
                this.authProperty = "Proxy-Authorization";
            }
            String authorization = null;

                .orElseThrow(() -> new FessSystemException("Cannot create an access token."));
    }

    /**
     * Generates and saves a new access token for the current session.
     * The token is used to authenticate API requests.
     */
    public void saveToken() {
        getSessionManager().setAttribute(Constants.SEARCH_ENGINE_API_ACCESS_TOKEN, UUID.randomUUID().toString().replace("-", ""));
    }

     |
    <server>
      <id>deploymentRepo</id>
      <username>repouser</username>
      <password>repopwd</password>
    </server>
    -->

    <!-- Another sample, using keys to authenticate.
    <server>
      <id>siteServer</id>
      <privateKey>/path/to/private/key</privateKey>
      <passphrase>optional; leave empty if not used.</passphrase>
    </server>
    -->
  </servers>

            return false;
        }

        @Override
        public boolean isRequestedSessionIdFromURL() {
            return false;
        }

        @Override
        public boolean authenticate(HttpServletResponse response) throws IOException, ServletException {
            return false;
        }

        @Override
        public void login(String username, String password) throws ServletException {

     * 13.5.1.
     */
    private fun isEndToEnd(fieldName: String): Boolean =
      !"Connection".equals(fieldName, ignoreCase = true) &&
        !"Keep-Alive".equals(fieldName, ignoreCase = true) &&
        !"Proxy-Authenticate".equals(fieldName, ignoreCase = true) &&
        !"Proxy-Authorization".equals(fieldName, ignoreCase = true) &&
        !"TE".equals(fieldName, ignoreCase = true) &&
        !"Trailers".equals(fieldName, ignoreCase = true) &&