/*
    * Copyright 2013–2024 Michael Osipov
    *
    * 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.
   */
  package net.sf.michaelo.tomcat.authenticator;
  
  import java.io.IOException;
  import java.security.Principal;
  import java.security.PrivilegedActionException;
  import java.security.PrivilegedExceptionAction;
  import java.util.Base64;
  
  import javax.security.auth.Subject;
  import javax.security.auth.login.LoginContext;
  import javax.security.auth.login.LoginException;
  import javax.servlet.http.HttpServletResponse;
  
  import org.apache.catalina.Realm;
  import org.apache.catalina.connector.Request;
  import org.apache.commons.lang3.StringUtils;
  import org.ietf.jgss.GSSContext;
  import org.ietf.jgss.GSSCredential;
  import org.ietf.jgss.GSSException;
  import org.ietf.jgss.GSSManager;
  import org.ietf.jgss.GSSName;
  
  /**
   * A SPNEGO Authenticator which utilizes GSS-API to authenticate a client.
   */
  public class SpnegoAuthenticator extends GSSAuthenticatorBase {
  
  	protected static final String SPNEGO_METHOD = "SPNEGO";
  	protected static final String SPNEGO_AUTH_SCHEME = "Negotiate";
  
  	private static final byte[] NTLM_TYPE1_MESSAGE_START = { (byte) 'N', (byte) 'T', (byte) 'L',
  			(byte) 'M', (byte) 'S', (byte) 'S', (byte) 'P', (byte) '\0', (byte) 0x01, (byte) 0x00,
  			(byte) 0x00, (byte) 0x00 };
  
  	@Override
  	protected boolean doAuthenticate(Request request, HttpServletResponse response)
  			throws IOException {
  
  		if (checkForCachedAuthentication(request, response, true)) {
  			return true;
  		}
  
  		String authorization = request.getHeader("Authorization");
  
  		if (!StringUtils.startsWithIgnoreCase(authorization, SPNEGO_AUTH_SCHEME)) {
  			sendUnauthorized(request, response, SPNEGO_AUTH_SCHEME);
  			return false;
  		}
  
  		String authorizationValue = StringUtils.substring(authorization,
  				SPNEGO_AUTH_SCHEME.length() + 1);
  
  		if (StringUtils.isEmpty(authorizationValue)) {
  			sendUnauthorized(request, response, SPNEGO_AUTH_SCHEME);
  			return false;
  		}
  
  		byte[] outToken = null;
  		byte[] inToken = null;
  
  		if (logger.isDebugEnabled())
  			logger.debug(sm.getString("spnegoAuthenticator.processingToken", authorizationValue));
  
  		try {
  			inToken = Base64.getDecoder().decode(authorizationValue);
  		} catch (Exception e) {
  			logger.warn(sm.getString("spnegoAuthenticator.incorrectlyEncodedToken",
  					authorizationValue), e);
  
  			sendUnauthorized(request, response, SPNEGO_AUTH_SCHEME,
  					"spnegoAuthenticator.incorrectlyEncodedToken.responseMessage");
  			return false;
  		}
  
  		if (inToken.length >= NTLM_TYPE1_MESSAGE_START.length) {
  			boolean ntlmDetected = false;
  			for (int i = 0; i < NTLM_TYPE1_MESSAGE_START.length; i++) {
  				ntlmDetected = inToken[i] == NTLM_TYPE1_MESSAGE_START[i];
  
  				if (!ntlmDetected)
  					break;
  			}
  
  			if (ntlmDetected) {
 				logger.warn(sm.getString("spnegoAuthenticator.ntlmNotSupported"));
 
 				sendUnauthorized(request, response, SPNEGO_AUTH_SCHEME,
 						"spnegoAuthenticator.ntlmNotSupported.responseMessage");
 				return false;
 			}
 		}
 
 		LoginContext lc = null;
 		GSSContext gssContext = null;
 		Principal principal = null;
 
 		try {
 			try {
 				lc = new LoginContext(getLoginEntryName());
 				lc.login();
 			} catch (LoginException e) {
 				logger.error(sm.getString("spnegoAuthenticator.obtainFailed"), e);
 
 				sendInternalServerError(request, response, "spnegoAuthenticator.obtainFailed");
 				return false;
 			}
 
 			final GSSManager manager = GSSManager.getInstance();
 			final PrivilegedExceptionAction<GSSCredential> action = () -> manager.createCredential(null,
 					GSSCredential.INDEFINITE_LIFETIME, SPNEGO_MECHANISM, GSSCredential.ACCEPT_ONLY);
 
 			try {
 				gssContext = manager.createContext(Subject.doAs(lc.getSubject(), action));
 			} catch (PrivilegedActionException e) {
 				logger.error(sm.getString("spnegoAuthenticator.obtainFailed"), e.getException());
 
 				sendInternalServerError(request, response, "spnegoAuthenticator.obtainFailed");
 				return false;
 			} catch (GSSException e) {
 				logger.error(sm.getString("spnegoAuthenticator.createContextFailed"), e);
 
 				sendInternalServerError(request, response,
 						"spnegoAuthenticator.createContextFailed");
 				return false;
 			}
 
 			try {
 				outToken = gssContext.acceptSecContext(inToken, 0, inToken.length);
 			} catch (GSSException e) {
 				logger.warn(sm.getString("spnegoAuthenticator.invalidToken", authorizationValue), e);
 
 				sendUnauthorized(request, response, SPNEGO_AUTH_SCHEME,
 						"spnegoAuthenticator.invalidToken.responseMessage");
 				return false;
 			}
 
 			try {
 				if (gssContext.isEstablished()) {
 					if (logger.isDebugEnabled())
 						logger.debug(sm.getString("spnegoAuthenticator.contextSuccessfullyEstablished"));
 
 					Realm realm = context.getRealm();
 					principal = realm.authenticate(gssContext, isStoreDelegatedCredential());
 
 					if (principal == null) {
 						GSSName srcName = gssContext.getSrcName();
 						sendUnauthorized(request, response, SPNEGO_AUTH_SCHEME,
 								"gssAuthenticatorBase.userNotFound", srcName);
 						return false;
 					}
 				} else {
 					logger.error(sm.getString("spnegoAuthenticator.continueContextNotSupported"));
 
 					sendInternalServerError(request, response,
 							"spnegoAuthenticator.continueContextNotSupported.responseMessage");
 					return false;
 				}
 			} catch (GSSException e) {
 				logger.error(sm.getString("gssAuthenticatorBase.inquireNameFailed"), e);
 
 				sendInternalServerError(request, response, "gssAuthenticatorBase.inquireNameFailed");
 				return false;
 			}
 		} finally {
 			if (gssContext != null) {
 				try {
 					gssContext.dispose();
 				} catch (GSSException e) {
 					; // Ignore
 				}
 			}
 			if (lc != null) {
 				try {
 					lc.logout();
 				} catch (LoginException e) {
 					; // Ignore
 				}
 			}
 		}
 
 		register(request, response, principal, SPNEGO_METHOD, principal.getName(), null);
 
 		if (outToken != null) {
 			String authenticationValue = Base64.getEncoder().encodeToString(outToken);
 			if (logger.isDebugEnabled())
 				logger.debug(sm.getString("spnegoAuthenticator.respondingWithToken", authenticationValue));
 
 			response.setHeader(AUTH_HEADER_NAME, SPNEGO_AUTH_SCHEME + " " + authenticationValue);
 		}
 
 		return true;
 	}
 
 	@Override
 	protected boolean isPreemptiveAuthPossible(Request request) {
 		String authorization = request.getHeader("Authorization");
 
 		return StringUtils.startsWithIgnoreCase(authorization, SPNEGO_AUTH_SCHEME);
 	}
 
 	@Override
 	protected String getAuthMethod() {
 		return SPNEGO_METHOD;
 	}
 
 }