/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.shiro.web.filter.authz;

import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletResponse;

/**
 * Filter which requires a request to be over SSL.  Access is allowed if the request is received on the configured
 * server {@link #setPort(int) port} <em>and</em> the
 * {@code request.}{@link javax.servlet.ServletRequest#isSecure() isSecure()}.  If either condition is {@code false},
 * the filter chain will not continue.
 * <p/>
 * The {@link #getPort() port} property defaults to {@code 443} and also additionally guarantees that the
 * request scheme is always 'https' (except for port 80, which retains the 'http' scheme).
 * <p/>
 * In addition the filter allows enabling HTTP Strict Transport Security (HSTS).
 * This feature is opt-in and disabled by default. If enabled HSTS
 * will prevent <b>any</b> communications from being sent over HTTP to the 
 * specified domain and will instead send all communications over HTTPS.
 * </p>
 * The {@link #getMaxAge() maxAge} property defaults {@code 31536000}, and 
 * {@link #isIncludeSubDomains includeSubDomains} is {@code false}.
 * </p>
 * <b>Warning:</b> Use this setting with care and only if you plan to enable 
 * SSL on every path.
 * </p>
 * Example configs:
 * <pre>
 * [urls]
 * /secure/path/** = ssl
 * </pre>
 * with HSTS enabled
 * <pre>
 * [main]
 * ssl.hsts.enabled = true
 * [urls]
 * /** = ssl
 * </pre>
 * @since 1.0
 * @see <a href="https://tools.ietf.org/html/rfc6797">HTTP Strict Transport Security (HSTS)</a>
 */
public class SslFilter extends PortFilter {

    public static final int DEFAULT_HTTPS_PORT = 443;
    public static final String HTTPS_SCHEME = "https";
    
    private HSTS hsts;

    public SslFilter() {
        setPort(DEFAULT_HTTPS_PORT);
        this.hsts = new HSTS();
    }

    public HSTS getHsts() {
        return hsts;
    }

    public void setHsts(HSTS hsts) {
        this.hsts = hsts;
    }

    @Override
    protected String getScheme(String requestScheme, int port) {
        if (port == DEFAULT_HTTP_PORT) {
            return PortFilter.HTTP_SCHEME;
        } else {
            return HTTPS_SCHEME;
        }
    }

    /**
     * Retains the parent method's port-matching behavior but additionally guarantees that the
     *{@code ServletRequest.}{@link javax.servlet.ServletRequest#isSecure() isSecure()}.  If the port does not match or
     * the request is not secure, access is denied.
     *
     * @param request     the incoming {@code ServletRequest}
     * @param response    the outgoing {@code ServletResponse} - ignored in this implementation
     * @param mappedValue the filter-specific config value mapped to this filter in the URL rules mappings - ignored by this implementation.
     * @return {@code true} if the request is received on an expected SSL port and the
     * {@code request.}{@link javax.servlet.ServletRequest#isSecure() isSecure()}, {@code false} otherwise.
     * @throws Exception if the call to {@code super.isAccessAllowed} throws an exception.
     * @since 1.2
     */
    @Override
    protected boolean isAccessAllowed(ServletRequest request, ServletResponse response, Object mappedValue) throws Exception {
        return super.isAccessAllowed(request, response, mappedValue) && request.isSecure();
    }

    /**
     * If HTTP Strict Transport Security (HSTS) is enabled the HTTP header
     * will be written, otherwise this method does nothing.
     * @param request the incoming {@code ServletRequest}
     * @param response the outgoing {@code ServletResponse}
     */
    @Override
    protected void postHandle(ServletRequest request, ServletResponse response)  {
        if (hsts.isEnabled()) {
            StringBuilder directives = new StringBuilder(64)
                    .append("max-age=").append(hsts.getMaxAge());
            
            if (hsts.isIncludeSubDomains()) {
                directives.append("; includeSubDomains");
            }
            
            HttpServletResponse resp = (HttpServletResponse) response;
            resp.addHeader(HSTS.HTTP_HEADER, directives.toString());
        }
    }
    
    /**
     * Helper class for HTTP Strict Transport Security (HSTS)
     */
    public class HSTS {
        
        public static final String HTTP_HEADER = "Strict-Transport-Security";
        
        public static final boolean DEFAULT_ENABLED = false;
        public static final int DEFAULT_MAX_AGE = 31536000; // approx. one year in seconds
        public static final boolean DEFAULT_INCLUDE_SUB_DOMAINS = false;
        
        private boolean enabled;
        private int maxAge;
        private boolean includeSubDomains;
        
        public HSTS() {
            this.enabled = DEFAULT_ENABLED;
            this.maxAge = DEFAULT_MAX_AGE;
            this.includeSubDomains = DEFAULT_INCLUDE_SUB_DOMAINS;
        }

        public boolean isEnabled() {
            return enabled;
        }

        public void setEnabled(boolean enabled) {
            this.enabled = enabled;
        }

        public int getMaxAge() {
            return maxAge;
        }

        public void setMaxAge(int maxAge) {
            this.maxAge = maxAge;
        }

        public boolean isIncludeSubDomains() {
            return includeSubDomains;
        }

        public void setIncludeSubDomains(boolean includeSubDomains) {
            this.includeSubDomains = includeSubDomains;
        }
    }
}