/**
 * 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.ranger.security.web.filter;

import org.apache.commons.lang.StringUtils;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.security.authentication.client.AuthenticatedURL;
import org.apache.hadoop.security.authentication.client.AuthenticationException;
import org.apache.hadoop.security.authentication.client.KerberosAuthenticator;
import org.apache.hadoop.security.authentication.server.AuthenticationHandler;
import org.apache.hadoop.security.authentication.server.AuthenticationToken;
import org.apache.hadoop.security.authentication.server.KerberosAuthenticationHandler;
import org.apache.hadoop.security.authentication.server.PseudoAuthenticationHandler;
import org.apache.hadoop.security.authentication.util.*;
import org.apache.ranger.common.PropertiesUtil;
import org.apache.ranger.plugin.util.RangerCommonConstants;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletContext;
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.EOFException;
import java.io.IOException;
import java.security.Principal;
import java.text.SimpleDateFormat;
import java.util.*;

import static com.google.common.io.ByteStreams.skipFully;

@InterfaceAudience.Private
@InterfaceStability.Unstable
public class RangerKrbFilter implements Filter {

    private static final Logger LOG = LoggerFactory.getLogger(RangerKrbFilter.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";

  public static final String SIGNATURE_SECRET_FILE = SIGNATURE_SECRET + ".file";

  /**
   * 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";

  /**
   * Constant for the configuration property that indicates the name of the
   * SignerSecretProvider class to use.
   * Possible values are: "string", "random", "zookeeper", or a classname.
   * If not specified, the "string" implementation will be used with
   * SIGNATURE_SECRET; and if that's not specified, the "random" implementation
   * will be used.
   */
  public static final String SIGNER_SECRET_PROVIDER =
          "signer.secret.provider";

  /**
   * Constant for the ServletContext attribute that can be used for providing a
   * custom implementation of the SignerSecretProvider. Note that the class
   * should already be initialized. If not specified, SIGNER_SECRET_PROVIDER
   * will be used.
   */
  public static final String SIGNER_SECRET_PROVIDER_ATTRIBUTE =
      "signer.secret.provider.object";

  private static final String BROWSER_USER_AGENT_PARAM = "ranger.krb.browser-useragents-regex";

  static final String ALLOW_TRUSTED_PROXY = "ranger.authentication.allow.trustedproxy";

  private String[] browserUserAgents;

  private Properties config;
  private Signer signer;
  private SignerSecretProvider secretProvider;
  private AuthenticationHandler authHandler;
  private long validity;
  private String cookieDomain;
  private String cookiePath;
  private String cookieName;

  /**
   * <p>Initializes the authentication filter and signer secret provider.</p>
   * It instantiates and initializes the specified {@link
   * AuthenticationHandler}.
   *
   * @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 + "." : "";
    config = getConfiguration(configPrefix, filterConfig);
    String authHandlerName = config.getProperty(AUTH_TYPE, null);
    String authHandlerClassName;
    if (authHandlerName == null) {
      throw new ServletException("Authentication type must be specified: " +
          PseudoAuthenticationHandler.TYPE + "|" +
          KerberosAuthenticationHandler.TYPE + "|<class>");
    }
    if(StringUtils.equalsIgnoreCase(authHandlerName, PseudoAuthenticationHandler.TYPE)){
      authHandlerClassName = PseudoAuthenticationHandler.class.getName();
    }else if(StringUtils.equalsIgnoreCase(authHandlerName, KerberosAuthenticationHandler.TYPE)){
      authHandlerClassName = KerberosAuthenticationHandler.class.getName();
    } else {
      authHandlerClassName = authHandlerName;
    }

    validity = Long.parseLong(config.getProperty(AUTH_TOKEN_VALIDITY, "36000"))
        * 1000; //10 hours
    initializeSecretProvider(filterConfig);

    initializeAuthHandler(authHandlerClassName, filterConfig);

    cookieDomain = config.getProperty(COOKIE_DOMAIN, null);
    cookiePath = config.getProperty(COOKIE_PATH, null);
    cookieName = config.getProperty(RangerCommonConstants.PROP_COOKIE_NAME, RangerCommonConstants.DEFAULT_COOKIE_NAME);
  }

  protected void initializeAuthHandler(String authHandlerClassName, FilterConfig filterConfig)
      throws ServletException {
    try {
      Class<?> klass = Thread.currentThread().getContextClassLoader().loadClass(authHandlerClassName);
      authHandler = (AuthenticationHandler) klass.newInstance();
      authHandler.init(config);
    } catch (ClassNotFoundException | InstantiationException |
        IllegalAccessException ex) {
      throw new ServletException(ex);
    }
  }

  protected void initializeSecretProvider(FilterConfig filterConfig)
      throws ServletException {
    secretProvider = (SignerSecretProvider) filterConfig.getServletContext().
        getAttribute(SIGNER_SECRET_PROVIDER_ATTRIBUTE);
    if (secretProvider == null) {
      // As tomcat cannot specify the provider object in the configuration.
      // It'll go into this path
      try {
        secretProvider = constructSecretProvider(
            filterConfig.getServletContext(),
            config, false);
      } catch (Exception ex) {
        throw new ServletException(ex);
      }
    }
    signer = new Signer(secretProvider);
  }

  public static SignerSecretProvider constructSecretProvider(
      ServletContext ctx, Properties config,
      	boolean disallowFallbackToRandomSecretProvider) throws Exception {
		long validity = Long.parseLong(config.getProperty(AUTH_TOKEN_VALIDITY,
				"36000")) * 1000;

		String name = config.getProperty(SIGNER_SECRET_PROVIDER);
		if (StringUtils.isEmpty(name)) {
			if (!disallowFallbackToRandomSecretProvider) {
				name = "random";
			} else {
				name = "file";
			}
		}

    SignerSecretProvider provider;
    if ("file".equals(name)) {
      provider = new FileSignerSecretProvider();
      try {
        provider.init(config, ctx, validity);
      } catch (Exception e) {
        if (!disallowFallbackToRandomSecretProvider) {
          LOG.info("Unable to initialize FileSignerSecretProvider, " +
                       "falling back to use random secrets.");
          provider = new RandomSignerSecretProvider();
          provider.init(config, ctx, validity);
        } else {
          throw e;
        }
      }
    } else if ("random".equals(name)) {
      provider = new RandomSignerSecretProvider();
      provider.init(config, ctx, validity);
    } else if ("zookeeper".equals(name)) {
      provider = new ZKSignerSecretProvider();
      provider.init(config, ctx, validity);
    } else {
      provider = (SignerSecretProvider) Thread.currentThread().
          getContextClassLoader().loadClass(name).newInstance();
      provider.init(config, ctx, validity);
    }
    return provider;
  }

  /**
   * Returns the configuration properties of the {@link RangerKrbFilter}
   * without the prefix. The returned properties are the same that the
   * {@link #getConfiguration(String, FilterConfig)} method returned.
   *
   * @return the configuration properties.
   */
  protected Properties getConfiguration() {
    return config;
  }

  /**
   * 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 secretProvider != null && secretProvider.getClass() == RandomSignerSecretProvider.class;
  }

  /**
   * Returns if a custom implementation of a SignerSecretProvider is being used.
   *
   * @return if a custom implementation of a SignerSecretProvider is being used.
   */
  protected boolean isCustomSignerSecretProvider() {
	Class<?> clazz = secretProvider != null ? secretProvider.getClass() : null;
    return clazz != FileSignerSecretProvider.class && clazz !=
        RandomSignerSecretProvider.class && clazz != ZKSignerSecretProvider
        .class;
  }

  /**
   * 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();
    if(filterConfig != null){
	    Enumeration<?> names = filterConfig.getInitParameterNames();
	    if(names != null){
		    while (names.hasMoreElements()) {
		      String name = (String) names.nextElement();
		      if (name != null && configPrefix != null && 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 (AuthenticatedURL.AUTH_COOKIE.equals(cookie.getName())) {
          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 != null){
	      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 {
    boolean unauthorizedResponse = true;
    int errCode = HttpServletResponse.SC_UNAUTHORIZED;
    AuthenticationException authenticationEx = null;
    HttpServletRequest httpRequest = (HttpServletRequest) request;
    HttpServletResponse httpResponse = (HttpServletResponse) response;
    boolean isHttps = "https".equals(httpRequest.getScheme());
    boolean allowTrustedProxy = PropertiesUtil.getBooleanProperty(ALLOW_TRUSTED_PROXY, false);
    long contentLength = httpRequest.getContentLength();

    try {
      boolean newToken = false;
      AuthenticationToken token;
      try {
        token = getToken(httpRequest);
      }
      catch (AuthenticationException ex) {
    	ex.printStackTrace();
        LOG.warn("AuthenticationToken ignored: " + ex.getMessage());
        // will be sent back in a 401 unless filter authenticates
        authenticationEx = ex;
        token = null;
      }

      if (authHandler.managementOperation(token, httpRequest, httpResponse)) {
        if (token == null) {
          if (LOG.isDebugEnabled()) {
            LOG.debug("Request [{}] triggering authentication", getRequestURL(httpRequest));
          }
          token = authHandler.authenticate(httpRequest, httpResponse);
          if (token != null && token.getExpires() != 0 &&
              token != AuthenticationToken.ANONYMOUS) {
            token.setExpires(System.currentTimeMillis() + getValidity() * 1000);
          }
          newToken = true;
        }
        if (token != null) {
          unauthorizedResponse = false;
          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 || allowTrustedProxy) && !token.isExpired() && token != AuthenticationToken.ANONYMOUS) {
            String signedToken = signer.sign(token.toString());
            createAuthCookie(httpResponse, signedToken, getCookieDomain(),
                    getCookiePath(), token.getExpires(), isHttps);
          }
          doFilter(filterChain, httpRequest, httpResponse);
        }
      } else {
        unauthorizedResponse = false;
      }
    } catch (AuthenticationException ex) {
      // exception from the filter itself is fatal
      ex.printStackTrace();
      errCode = HttpServletResponse.SC_FORBIDDEN;
      authenticationEx = ex;
      LOG.warn("Authentication exception: " + ex.getMessage(), ex);
    }
    if (unauthorizedResponse) {
      if (!httpResponse.isCommitted()) {
        if (LOG.isDebugEnabled()) {
          LOG.debug("create auth cookie");
        }
        createAuthCookie(httpResponse, "", getCookieDomain(),
                getCookiePath(), 0, isHttps);
        // If response code is 401. Then WWW-Authenticate Header should be
        // present.. reset to 403 if not found..
        if ((errCode == HttpServletResponse.SC_UNAUTHORIZED)
            && (!httpResponse.containsHeader(
                KerberosAuthenticator.WWW_AUTHENTICATE))) {
          errCode = HttpServletResponse.SC_FORBIDDEN;
        }
        if (authenticationEx == null) {
            String agents = PropertiesUtil.getProperty(BROWSER_USER_AGENT_PARAM, RangerCSRFPreventionFilter.BROWSER_USER_AGENTS_DEFAULT);
            if (agents == null) {
              agents = RangerCSRFPreventionFilter.BROWSER_USER_AGENTS_DEFAULT;
            }
            parseBrowserUserAgents(agents);
            if(isBrowser(httpRequest.getHeader(RangerCSRFPreventionFilter.HEADER_USER_AGENT)) && !allowTrustedProxy){
        	  ((HttpServletResponse)response).setHeader(KerberosAuthenticator.WWW_AUTHENTICATE, "");
                filterChain.doFilter(request, response);
            }else{
              if (allowTrustedProxy) {
                String expectHeader = httpRequest.getHeader("Expect");
                if (LOG.isDebugEnabled()) {
                  LOG.debug("expect header in request = " + expectHeader);
                  LOG.debug("http response code = " + httpResponse.getStatus());
                }
                if (expectHeader != null && expectHeader.startsWith("100")) {
                  if (LOG.isDebugEnabled()) {
                    LOG.debug("skipping 100 continue!!");
                  }
                  if (contentLength <= 0) {
                    Integer maxContentLen = Integer.MAX_VALUE;
                    contentLength = maxContentLen.longValue();
                    try {
                      if (LOG.isDebugEnabled()) {
                        LOG.debug("Skipping content length of " + contentLength);
                      }
                      skipFully(request.getInputStream(), contentLength);
                    } catch (EOFException ex) {
                      LOG.info(ex.getMessage());
                    }
                  }
                }
              }
              boolean chk = true;
              Collection<String> headerNames = httpResponse.getHeaderNames();
              if (LOG.isDebugEnabled()) {
                LOG.debug("reponse header names = " + headerNames);
              }
              for(String headerName : headerNames){
                String value = httpResponse.getHeader(headerName);
                if("Set-Cookie".equalsIgnoreCase(headerName) && value.startsWith(cookieName)){
                  chk = false;
                  break;
                }
              }
              String authHeader = httpRequest.getHeader("Authorization");
              if(authHeader == null && chk){
	            	filterChain.doFilter(request, response);
	            }else if(authHeader != null && authHeader.startsWith("Basic")){
	                filterChain.doFilter(request, response);
	            }
        	}
        } else {
          httpResponse.sendError(errCode, authenticationEx.getMessage());
        }
      }
    }
  }

  /**
   * Delegates call to the servlet filter chain. Sub-classes my override this
   * method to perform pre and post tasks.
   */
  protected void doFilter(FilterChain filterChain, HttpServletRequest request,
      HttpServletResponse response) throws IOException, ServletException {
    filterChain.doFilter(request, response);
  }

  /**
   * Creates the Hadoop authentication HTTP cookie.
   *
   * @param token authentication token for the cookie.
   * @param expires UNIX timestamp that indicates the expire date of the
   *                cookie. It has no effect if its value &lt; 0.
   *
   * XXX the following code duplicate some logic in Jetty / Servlet API,
   * because of the fact that Hadoop is stuck at servlet 2.5 and jetty 6
   * right now.
   */
  public static void createAuthCookie(HttpServletResponse resp, String token,
                                      String domain, String path, long expires,
                                      boolean isSecure) {
    StringBuilder sb = new StringBuilder(AuthenticatedURL.AUTH_COOKIE)
                           .append("=");
    if (token != null && token.length() > 0) {
      sb.append("\"").append(token).append("\"");
    }

    if (path != null) {
      sb.append("; Path=").append(path);
    }

    if (domain != null) {
      sb.append("; Domain=").append(domain);
    }

    if (expires >= 0) {
      Date date = new Date(expires);
      SimpleDateFormat df = new SimpleDateFormat("EEE, " +
              "dd-MMM-yyyy HH:mm:ss zzz");
      df.setTimeZone(TimeZone.getTimeZone("GMT"));
      sb.append("; Expires=").append(df.format(date));
    }

    if (isSecure) {
      sb.append("; Secure");
    }

    sb.append("; HttpOnly");
    resp.addHeader("Set-Cookie", sb.toString());
  }

	void parseBrowserUserAgents(String userAgents) {
		browserUserAgents = userAgents.split(",");
	}

	protected boolean isBrowser(String userAgent) {
		boolean isWeb = false;
		if (browserUserAgents != null && browserUserAgents.length > 0 && userAgent != null) {
			for (String ua : browserUserAgents) {
				if (userAgent.toLowerCase().startsWith(ua.toLowerCase())) {
					isWeb = true;
					break;
				}
			}
		}
		return isWeb;
	}
}