/*
 * Copyright 1999,2004 The Apache Software Foundation.
 * 
 * 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 org.apache.catalina.authenticator;


import java.io.IOException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.Principal;
import java.util.Hashtable;
import java.util.StringTokenizer;

import javax.servlet.http.HttpServletResponse;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.apache.catalina.Realm;
import org.apache.catalina.connector.Request;
import org.apache.catalina.connector.Response;
import org.apache.catalina.deploy.LoginConfig;
import org.apache.catalina.util.MD5Encoder;


/**
 * An <b>Authenticator</b> and <b>Valve</b> implementation of HTTP DIGEST
 * Authentication (see RFC 2069).
 *
 * @author Craig R. McClanahan
 * @author Remy Maucherat
 * @version $Revision$ $Date$
 */

public class DigestAuthenticator
    extends AuthenticatorBase {
    private static Log log = LogFactory.getLog(DigestAuthenticator.class);


    // -------------------------------------------------------------- Constants


    /**
     * Indicates that no once tokens are used only once.
     */
    protected static final int USE_ONCE = 1;


    /**
     * Indicates that no once tokens are used only once.
     */
    protected static final int USE_NEVER_EXPIRES = Integer.MAX_VALUE;


    /**
     * Indicates that no once tokens are used only once.
     */
    protected static final int TIMEOUT_INFINITE = Integer.MAX_VALUE;


    /**
     * The MD5 helper object for this class.
     */
    protected static final MD5Encoder md5Encoder = new MD5Encoder();


    /**
     * Descriptive information about this implementation.
     */
    protected static final String info =
        "org.apache.catalina.authenticator.DigestAuthenticator/1.0";


    // ----------------------------------------------------------- Constructors


    public DigestAuthenticator() {
        super();
        try {
            if (md5Helper == null)
                md5Helper = MessageDigest.getInstance("MD5");
        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
            throw new IllegalStateException();
        }
    }


    // ----------------------------------------------------- Instance Variables


    /**
     * MD5 message digest provider.
     */
    protected static MessageDigest md5Helper;


    /**
     * No once hashtable.
     */
    protected Hashtable nOnceTokens = new Hashtable();


    /**
     * No once expiration (in millisecond). A shorter amount would mean a
     * better security level (since the token is generated more often), but at
     * the expense of a bigger server overhead.
     */
    protected long nOnceTimeout = TIMEOUT_INFINITE;


    /**
     * No once expiration after a specified number of uses. A lower number
     * would produce more overhead, since a token would have to be generated
     * more often, but would be more secure.
     */
    protected int nOnceUses = USE_ONCE;


    /**
     * Private key.
     */
    protected String key = "Catalina";


    // ------------------------------------------------------------- Properties


    /**
     * Return descriptive information about this Valve implementation.
     */
    public String getInfo() {

        return (info);

    }


    // --------------------------------------------------------- Public Methods


    /**
     * Authenticate the user making this request, based on the specified
     * login configuration.  Return <code>true</code> if any specified
     * constraint has been satisfied, or <code>false</code> if we have
     * created a response challenge already.
     *
     * @param request Request we are processing
     * @param response Response we are creating
     * @param config    Login configuration describing how authentication
     *              should be performed
     *
     * @exception IOException if an input/output error occurs
     */
    public boolean authenticate(Request request,
                                Response response,
                                LoginConfig config)
        throws IOException {

        // Have we already authenticated someone?
        Principal principal = request.getUserPrincipal();
        //String ssoId = (String) request.getNote(Constants.REQ_SSOID_NOTE);
        if (principal != null) {
            if (log.isDebugEnabled())
                log.debug("Already authenticated '" + principal.getName() + "'");
            // Associate the session with any existing SSO session in order
            // to get coordinated session invalidation at logout
            String ssoId = (String) request.getNote(Constants.REQ_SSOID_NOTE);
            if (ssoId != null)
                associate(ssoId, request.getSessionInternal(true));
            return (true);
        }

        // NOTE: We don't try to reauthenticate using any existing SSO session,
        // because that will only work if the original authentication was
        // BASIC or FORM, which are less secure than the DIGEST auth-type
        // specified for this webapp
        //
        // Uncomment below to allow previous FORM or BASIC authentications
        // to authenticate users for this webapp
        // TODO make this a configurable attribute (in SingleSignOn??)
        /*
        // Is there an SSO session against which we can try to reauthenticate?
        if (ssoId != null) {
            if (log.isDebugEnabled())
                log.debug("SSO Id " + ssoId + " set; attempting " +
                          "reauthentication");
            // Try to reauthenticate using data cached by SSO.  If this fails,
            // either the original SSO logon was of DIGEST or SSL (which
            // we can't reauthenticate ourselves because there is no
            // cached username and password), or the realm denied
            // the user's reauthentication for some reason.
            // In either case we have to prompt the user for a logon
            if (reauthenticateFromSSO(ssoId, request))
                return true;
        }
        */

        // Validate any credentials already included with this request
        String authorization = request.getHeader("authorization");
        if (authorization != null) {
            principal = findPrincipal(request, authorization, context.getRealm());
            if (principal != null) {
                String username = parseUsername(authorization);
                register(request, response, principal,
                         Constants.DIGEST_METHOD,
                         username, null);
                return (true);
            }
        }

        // Send an "unauthorized" response and an appropriate challenge

        // Next, generate a nOnce token (that is a token which is supposed
        // to be unique).
        String nOnce = generateNOnce(request);

        setAuthenticateHeader(request, response, config, nOnce);
        response.setStatus(HttpServletResponse.SC_UNAUTHORIZED);
        //      hres.flushBuffer();
        return (false);

    }


    // ------------------------------------------------------ Protected Methods


    /**
     * Parse the specified authorization credentials, and return the
     * associated Principal that these credentials authenticate (if any)
     * from the specified Realm.  If there is no such Principal, return
     * <code>null</code>.
     *
     * @param request HTTP servlet request
     * @param authorization Authorization credentials from this request
     * @param realm Realm used to authenticate Principals
     */
    protected static Principal findPrincipal(Request request,
                                             String authorization,
                                             Realm realm) {

        //System.out.println("Authorization token : " + authorization);
        // Validate the authorization credentials format
        if (authorization == null)
            return (null);
        if (!authorization.startsWith("Digest "))
            return (null);
        authorization = authorization.substring(7).trim();


        StringTokenizer commaTokenizer =
            new StringTokenizer(authorization, ",");

        String userName = null;
        String realmName = null;
        String nOnce = null;
        String nc = null;
        String cnonce = null;
        String qop = null;
        String uri = null;
        String response = null;
        String method = request.getMethod();

        while (commaTokenizer.hasMoreTokens()) {
            String currentToken = commaTokenizer.nextToken();
            int equalSign = currentToken.indexOf('=');
            if (equalSign < 0)
                return null;
            String currentTokenName =
                currentToken.substring(0, equalSign).trim();
            String currentTokenValue =
                currentToken.substring(equalSign + 1).trim();
            if ("username".equals(currentTokenName))
                userName = removeQuotes(currentTokenValue);
            if ("realm".equals(currentTokenName))
                realmName = removeQuotes(currentTokenValue, true);
            if ("nonce".equals(currentTokenName))
                nOnce = removeQuotes(currentTokenValue);
            if ("nc".equals(currentTokenName))
                nc = removeQuotes(currentTokenValue);
            if ("cnonce".equals(currentTokenName))
                cnonce = removeQuotes(currentTokenValue);
            if ("qop".equals(currentTokenName))
                qop = removeQuotes(currentTokenValue);
            if ("uri".equals(currentTokenName))
                uri = removeQuotes(currentTokenValue);
            if ("response".equals(currentTokenName))
                response = removeQuotes(currentTokenValue);
        }

        if ( (userName == null) || (realmName == null) || (nOnce == null)
             || (uri == null) || (response == null) )
            return null;

        // Second MD5 digest used to calculate the digest :
        // MD5(Method + ":" + uri)
        String a2 = method + ":" + uri;
        //System.out.println("A2:" + a2);

        String md5a2 = md5Encoder.encode(md5Helper.digest(a2.getBytes()));

        return (realm.authenticate(userName, response, nOnce, nc, cnonce, qop,
                                   realmName, md5a2));

    }


    /**
     * Parse the username from the specified authorization string.  If none
     * can be identified, return <code>null</code>
     *
     * @param authorization Authorization string to be parsed
     */
    protected String parseUsername(String authorization) {

        //System.out.println("Authorization token : " + authorization);
        // Validate the authorization credentials format
        if (authorization == null)
            return (null);
        if (!authorization.startsWith("Digest "))
            return (null);
        authorization = authorization.substring(7).trim();

        StringTokenizer commaTokenizer =
            new StringTokenizer(authorization, ",");

        while (commaTokenizer.hasMoreTokens()) {
            String currentToken = commaTokenizer.nextToken();
            int equalSign = currentToken.indexOf('=');
            if (equalSign < 0)
                return null;
            String currentTokenName =
                currentToken.substring(0, equalSign).trim();
            String currentTokenValue =
                currentToken.substring(equalSign + 1).trim();
            if ("username".equals(currentTokenName))
                return (removeQuotes(currentTokenValue));
        }

        return (null);

    }


    /**
     * Removes the quotes on a string. RFC2617 states quotes are optional for
     * all parameters except realm.
     */
    protected static String removeQuotes(String quotedString,
                                         boolean quotesRequired) {
        //support both quoted and non-quoted
        if (quotedString.length() > 0 && quotedString.charAt(0) != '"' &&
                !quotesRequired) {
            return quotedString;
        } else if (quotedString.length() > 2) {
            return quotedString.substring(1, quotedString.length() - 1);
        } else {
            return new String();
        }
    }

    /**
     * Removes the quotes on a string.
     */
    protected static String removeQuotes(String quotedString) {
        return removeQuotes(quotedString, false);
    }

    /**
     * Generate a unique token. The token is generated according to the
     * following pattern. NOnceToken = Base64 ( MD5 ( client-IP ":"
     * time-stamp ":" private-key ) ).
     *
     * @param request HTTP Servlet request
     */
    protected String generateNOnce(Request request) {

        long currentTime = System.currentTimeMillis();

        String nOnceValue = request.getRemoteAddr() + ":" +
            currentTime + ":" + key;

        byte[] buffer = md5Helper.digest(nOnceValue.getBytes());
        nOnceValue = md5Encoder.encode(buffer);

        // Updating the value in the no once hashtable
        nOnceTokens.put(nOnceValue, new Long(currentTime + nOnceTimeout));

        return nOnceValue;
    }


    /**
     * Generates the WWW-Authenticate header.
     * <p>
     * The header MUST follow this template :
     * <pre>
     *      WWW-Authenticate    = "WWW-Authenticate" ":" "Digest"
     *                            digest-challenge
     *
     *      digest-challenge    = 1#( realm | [ domain ] | nOnce |
     *                  [ digest-opaque ] |[ stale ] | [ algorithm ] )
     *
     *      realm               = "realm" "=" realm-value
     *      realm-value         = quoted-string
     *      domain              = "domain" "=" <"> 1#URI <">
     *      nonce               = "nonce" "=" nonce-value
     *      nonce-value         = quoted-string
     *      opaque              = "opaque" "=" quoted-string
     *      stale               = "stale" "=" ( "true" | "false" )
     *      algorithm           = "algorithm" "=" ( "MD5" | token )
     * </pre>
     *
     * @param request HTTP Servlet request
     * @param response HTTP Servlet response
     * @param config    Login configuration describing how authentication
     *              should be performed
     * @param nOnce nonce token
     */
    protected void setAuthenticateHeader(Request request,
                                         Response response,
                                         LoginConfig config,
                                         String nOnce) {

        // Get the realm name
        String realmName = config.getRealmName();
        if (realmName == null)
            realmName = request.getServerName() + ":"
                + request.getServerPort();

        byte[] buffer = md5Helper.digest(nOnce.getBytes());

        String authenticateHeader = "Digest realm=\"" + realmName + "\", "
            +  "qop=\"auth\", nonce=\"" + nOnce + "\", " + "opaque=\""
            + md5Encoder.encode(buffer) + "\"";
        // System.out.println("Authenticate header value : "
        //                   + authenticateHeader);
        response.setHeader("WWW-Authenticate", authenticateHeader);

    }


}