/**
 * Licensed 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. See accompanying LICENSE file.
 */
package org.apache.hadoop.security.authentication.server;

import org.apache.hadoop.security.authentication.client.AuthenticatedURL;
import org.apache.hadoop.security.authentication.client.AuthenticationException;
import org.apache.hadoop.security.authentication.util.Signer;
import org.apache.hadoop.security.authentication.util.SignerException;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.security.Principal;
import java.util.Enumeration;
import java.util.Properties;
import java.util.Random;

/**
 * The {@link AuthenticationFilter} enables protecting web application resources with different (pluggable)
 * authentication mechanisms.
 * <p/>
 * Out of the box it provides 2 authentication mechanisms: Pseudo and Kerberos SPNEGO.
 * <p/>
 * Additional authentication mechanisms are supported via the {@link AuthenticationHandler} interface.
 * <p/>
 * This filter delegates to the configured authentication handler for authentication and once it obtains an
 * {@link AuthenticationToken} from it, sets a signed HTTP cookie with the token. For client requests
 * that provide the signed HTTP cookie, it verifies the validity of the cookie, extracts the user information
 * and lets the request proceed to the target resource.
 * <p/>
 * The supported configuration properties are:
 * <ul>
 * <li>config.prefix: indicates the prefix to be used by all other configuration properties, the default value
 * is no prefix. See below for details on how/why this prefix is used.</li>
 * <li>[#PREFIX#.]type: simple|kerberos|#CLASS#, 'simple' is short for the
 * {@link PseudoAuthenticationHandler}, 'kerberos' is short for {@link KerberosAuthenticationHandler}, otherwise
 * the full class name of the {@link AuthenticationHandler} must be specified.</li>
 * <li>[#PREFIX#.]signature.secret: the secret used to sign the HTTP cookie value. The default value is a random
 * value. Unless multiple webapp instances need to share the secret the random value is adequate.</li>
 * <li>[#PREFIX#.]token.validity: time -in seconds- that the generated token is valid before a
 * new authentication is triggered, default value is <code>3600</code> seconds.</li>
 * <li>[#PREFIX#.]cookie.domain: domain to use for the HTTP cookie that stores the authentication token.</li>
 * <li>[#PREFIX#.]cookie.path: path to use for the HTTP cookie that stores the authentication token.</li>
 * </ul>
 * <p/>
 * The rest of the configuration properties are specific to the {@link AuthenticationHandler} implementation and the
 * {@link AuthenticationFilter} will take all the properties that start with the prefix #PREFIX#, it will remove
 * the prefix from it and it will pass them to the the authentication handler for initialization. Properties that do
 * not start with the prefix will not be passed to the authentication handler initialization.
 */
public class AuthenticationFilter implements Filter {

  private static Logger LOG = LoggerFactory.getLogger(AuthenticationFilter.class);

  /**
   * Constant for the property that specifies the configuration prefix.
   */
  public static final String CONFIG_PREFIX = "config.prefix";

  /**
   * Constant for the property that specifies the authentication handler to use.
   */
  public static final String AUTH_TYPE = "type";

  /**
   * Constant for the property that specifies the secret to use for signing the HTTP Cookies.
   */
  public static final String SIGNATURE_SECRET = "signature.secret";

  /**
   * Constant for the configuration property that indicates the validity of the generated token.
   */
  public static final String AUTH_TOKEN_VALIDITY = "token.validity";

  /**
   * Constant for the configuration property that indicates the domain to use in the HTTP cookie.
   */
  public static final String COOKIE_DOMAIN = "cookie.domain";

  /**
   * Constant for the configuration property that indicates the path to use in the HTTP cookie.
   */
  public static final String COOKIE_PATH = "cookie.path";

  private static final Random RAN = new Random();

  private Signer signer;
  private AuthenticationHandler authHandler;
  private boolean randomSecret;
  private long validity;
  private String cookieDomain;
  private String cookiePath;

  /**
   * Initializes the authentication filter.
   * <p/>
   * It instantiates and initializes the specified {@link AuthenticationHandler}.
   * <p/>
   *
   * @param filterConfig filter configuration.
   *
   * @throws ServletException thrown if the filter or the authentication handler could not be initialized properly.
   */
  @Override
  public void init(FilterConfig filterConfig) throws ServletException {
    String configPrefix = filterConfig.getInitParameter(CONFIG_PREFIX);
    configPrefix = (configPrefix != null) ? configPrefix + "." : "";
    Properties config = getConfiguration(configPrefix, filterConfig);
    String authHandlerName = config.getProperty(AUTH_TYPE, null);
    String authHandlerClassName;
    if (authHandlerName == null) {
      throw new ServletException("Authentication type must be specified: simple|kerberos|<class>");
    }
    if (authHandlerName.equals("simple")) {
      authHandlerClassName = PseudoAuthenticationHandler.class.getName();
    } else if (authHandlerName.equals("kerberos")) {
      authHandlerClassName = KerberosAuthenticationHandler.class.getName();
    } else {
      authHandlerClassName = authHandlerName;
    }

    try {
      Class<?> klass = Thread.currentThread().getContextClassLoader().loadClass(authHandlerClassName);
      authHandler = (AuthenticationHandler) klass.newInstance();
      authHandler.init(config);
    } catch (ClassNotFoundException ex) {
      throw new ServletException(ex);
    } catch (InstantiationException ex) {
      throw new ServletException(ex);
    } catch (IllegalAccessException ex) {
      throw new ServletException(ex);
    }
    String signatureSecret = config.getProperty(configPrefix + SIGNATURE_SECRET);
    if (signatureSecret == null) {
      signatureSecret = Long.toString(RAN.nextLong());
      randomSecret = true;
      LOG.warn("'signature.secret' configuration not set, using a random value as secret");
    }
    signer = new Signer(signatureSecret.getBytes());
    validity = Long.parseLong(config.getProperty(AUTH_TOKEN_VALIDITY, "36000")) * 1000; //10 hours

    cookieDomain = config.getProperty(COOKIE_DOMAIN, null);
    cookiePath = config.getProperty(COOKIE_PATH, null);
  }

  /**
   * Returns the authentication handler being used.
   *
   * @return the authentication handler being used.
   */
  protected AuthenticationHandler getAuthenticationHandler() {
    return authHandler;
  }

  /**
   * Returns if a random secret is being used.
   *
   * @return if a random secret is being used.
   */
  protected boolean isRandomSecret() {
    return randomSecret;
  }

  /**
   * Returns the validity time of the generated tokens.
   *
   * @return the validity time of the generated tokens, in seconds.
   */
  protected long getValidity() {
    return validity / 1000;
  }

  /**
   * Returns the cookie domain to use for the HTTP cookie.
   *
   * @return the cookie domain to use for the HTTP cookie.
   */
  protected String getCookieDomain() {
    return cookieDomain;
  }

  /**
   * Returns the cookie path to use for the HTTP cookie.
   *
   * @return the cookie path to use for the HTTP cookie.
   */
  protected String getCookiePath() {
    return cookiePath;
  }

  /**
   * Destroys the filter.
   * <p/>
   * It invokes the {@link AuthenticationHandler#destroy()} method to release any resources it may hold.
   */
  @Override
  public void destroy() {
    if (authHandler != null) {
      authHandler.destroy();
      authHandler = null;
    }
  }

  /**
   * Returns the filtered configuration (only properties starting with the specified prefix). The property keys
   * are also trimmed from the prefix. The returned {@link Properties} object is used to initialized the
   * {@link AuthenticationHandler}.
   * <p/>
   * This method can be overriden by subclasses to obtain the configuration from other configuration source than
   * the web.xml file.
   *
   * @param configPrefix configuration prefix to use for extracting configuration properties.
   * @param filterConfig filter configuration object
   *
   * @return the configuration to be used with the {@link AuthenticationHandler} instance.
   *
   * @throws ServletException thrown if the configuration could not be created.
   */
  protected Properties getConfiguration(String configPrefix, FilterConfig filterConfig) throws ServletException {
    Properties props = new Properties();
    Enumeration<?> names = filterConfig.getInitParameterNames();
    while (names.hasMoreElements()) {
      String name = (String) names.nextElement();
      if (name.startsWith(configPrefix)) {
        String value = filterConfig.getInitParameter(name);
        props.put(name.substring(configPrefix.length()), value);
      }
    }
    return props;
  }

  /**
   * Returns the full URL of the request including the query string.
   * <p/>
   * Used as a convenience method for logging purposes.
   *
   * @param request the request object.
   *
   * @return the full URL of the request including the query string.
   */
  protected String getRequestURL(HttpServletRequest request) {
    StringBuffer sb = request.getRequestURL();
    if (request.getQueryString() != null) {
      sb.append("?").append(request.getQueryString());
    }
    return sb.toString();
  }

  /**
   * Returns the {@link AuthenticationToken} for the request.
   * <p/>
   * It looks at the received HTTP cookies and extracts the value of the {@link AuthenticatedURL#AUTH_COOKIE}
   * if present. It verifies the signature and if correct it creates the {@link AuthenticationToken} and returns
   * it.
   * <p/>
   * If this method returns <code>null</code> the filter will invoke the configured {@link AuthenticationHandler}
   * to perform user authentication.
   *
   * @param request request object.
   *
   * @return the Authentication token if the request is authenticated, <code>null</code> otherwise.
   *
   * @throws IOException thrown if an IO error occurred.
   * @throws AuthenticationException thrown if the token is invalid or if it has expired.
   */
  protected AuthenticationToken getToken(HttpServletRequest request) throws IOException, AuthenticationException {
    AuthenticationToken token = null;
    String tokenStr = null;
    Cookie[] cookies = request.getCookies();
    if (cookies != null) {
      for (Cookie cookie : cookies) {
        if (cookie.getName().equals(AuthenticatedURL.AUTH_COOKIE)) {
          tokenStr = cookie.getValue();
          try {
            tokenStr = signer.verifyAndExtract(tokenStr);
          } catch (SignerException ex) {
            throw new AuthenticationException(ex);
          }
          break;
        }
      }
    }
    if (tokenStr != null) {
      token = AuthenticationToken.parse(tokenStr);
      if (!token.getType().equals(authHandler.getType())) {
        throw new AuthenticationException("Invalid AuthenticationToken type");
      }
      if (token.isExpired()) {
        throw new AuthenticationException("AuthenticationToken expired");
      }
    }
    return token;
  }

  /**
   * If the request has a valid authentication token it allows the request to continue to the target resource,
   * otherwise it triggers an authentication sequence using the configured {@link AuthenticationHandler}.
   *
   * @param request the request object.
   * @param response the response object.
   * @param filterChain the filter chain object.
   *
   * @throws IOException thrown if an IO error occurred.
   * @throws ServletException thrown if a processing error occurred.
   */
  @Override
  public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain)
      throws IOException, ServletException {
    HttpServletRequest httpRequest = (HttpServletRequest) request;
    HttpServletResponse httpResponse = (HttpServletResponse) response;
    try {
      boolean newToken = false;
      AuthenticationToken token = getToken(httpRequest);
      if (token == null) {
        if (LOG.isDebugEnabled()) {
          LOG.debug("Request [{}] triggering authentication", getRequestURL(httpRequest));
        }
        token = authHandler.authenticate(httpRequest, httpResponse);
        if (token != null && token != AuthenticationToken.ANONYMOUS) {
          token.setExpires(System.currentTimeMillis() + getValidity() * 1000);
        }
        newToken = true;
      }
      if (token != null) {
        if (LOG.isDebugEnabled()) {
          LOG.debug("Request [{}] user [{}] authenticated", getRequestURL(httpRequest), token.getUserName());
        }
        final AuthenticationToken authToken = token;
        httpRequest = new HttpServletRequestWrapper(httpRequest) {

          @Override
          public String getAuthType() {
            return authToken.getType();
          }

          @Override
          public String getRemoteUser() {
            return authToken.getUserName();
          }

          @Override
          public Principal getUserPrincipal() {
            return (authToken != AuthenticationToken.ANONYMOUS) ? authToken : null;
          }
        };
        if (newToken && token != AuthenticationToken.ANONYMOUS) {
          String signedToken = signer.sign(token.toString());
          Cookie cookie = createCookie(signedToken);
          httpResponse.addCookie(cookie);
        }
        filterChain.doFilter(httpRequest, httpResponse);
      }
    } catch (AuthenticationException ex) {
      if (!httpResponse.isCommitted()) {
        Cookie cookie = createCookie("");
        cookie.setMaxAge(0);
        httpResponse.addCookie(cookie);
        httpResponse.sendError(HttpServletResponse.SC_UNAUTHORIZED, ex.getMessage());
      }
      LOG.warn("Authentication exception: " + ex.getMessage(), ex);
    }
  }

  /**
   * Creates the Hadoop authentiation HTTP cookie.
   * <p/>
   * It sets the domain and path specified in the configuration.
   *
   * @param token authentication token for the cookie.
   *
   * @return the HTTP cookie.
   */
  protected Cookie createCookie(String token) {
    Cookie cookie = new Cookie(AuthenticatedURL.AUTH_COOKIE, token);
    if (getCookieDomain() != null) {
      cookie.setDomain(getCookieDomain());
    }
    if (getCookiePath() != null) {
      cookie.setPath(getCookiePath());
    }
    return cookie;
  }
}