/*
 * 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.catalina.valves;

import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.security.NoSuchProviderException;
import java.security.cert.CertificateFactory;
import java.security.cert.X509Certificate;

import javax.servlet.ServletException;

import org.apache.catalina.Globals;
import org.apache.catalina.connector.Request;
import org.apache.catalina.connector.Response;
import org.apache.juli.logging.Log;
import org.apache.juli.logging.LogFactory;
import org.apache.tomcat.util.buf.UDecoder;

/**
 * When using mod_proxy_http, the client SSL information is not included in the protocol (unlike mod_jk and
 * mod_proxy_ajp). To make the client SSL information available to Tomcat, some additional configuration is required. In
 * httpd, mod_headers is used to add the SSL information as HTTP headers. In Tomcat, this valve is used to read the
 * information from the HTTP headers and insert it into the request.
 * <p>
 * <b>Note: Ensure that the headers are always set by httpd for all requests to prevent a client spoofing SSL
 * information by sending fake headers. </b>
 * <p>
 * In httpd.conf add the following:
 *
 * <pre>
 * &lt;IfModule ssl_module&gt;
 *   RequestHeader set SSL_CLIENT_CERT "%{SSL_CLIENT_CERT}s"
 *   RequestHeader set SSL_CIPHER "%{SSL_CIPHER}s"
 *   RequestHeader set SSL_SESSION_ID "%{SSL_SESSION_ID}s"
 *   RequestHeader set SSL_CIPHER_USEKEYSIZE "%{SSL_CIPHER_USEKEYSIZE}s"
 * &lt;/IfModule&gt;
 * </pre>
 *
 * In server.xml, configure this valve under the Engine element in server.xml:
 *
 * <pre>
 * &lt;Engine ...&gt;
 *   &lt;Valve className="org.apache.catalina.valves.SSLValve" /&gt;
 *   &lt;Host ... /&gt;
 * &lt;/Engine&gt;
 * </pre>
 */
public class SSLValve extends ValveBase {

    private static final Log log = LogFactory.getLog(SSLValve.class);

    private String sslClientCertHeader = "ssl_client_cert";
    private String sslClientEscapedCertHeader = "ssl_client_escaped_cert";
    private String sslCipherHeader = "ssl_cipher";
    private String sslSessionIdHeader = "ssl_session_id";
    private String sslCipherUserKeySizeHeader = "ssl_cipher_usekeysize";

    // ------------------------------------------------------ Constructor
    /**
     * Default constructor.
     */
    public SSLValve() {
        super(true);
    }


    /**
     * Returns the header name used to retrieve the client certificate.
     *
     * @return The client certificate header name
     */
    public String getSslClientCertHeader() {
        return sslClientCertHeader;
    }

    /**
     * Sets the header name used to retrieve the client certificate.
     *
     * @param sslClientCertHeader The client certificate header name
     */
    public void setSslClientCertHeader(String sslClientCertHeader) {
        this.sslClientCertHeader = sslClientCertHeader;
    }

    /**
     * Returns the header name used to retrieve the escaped client certificate.
     *
     * @return The escaped client certificate header name
     */
    public String getSslClientEscapedCertHeader() {
        return sslClientEscapedCertHeader;
    }

    /**
     * Sets the header name used to retrieve the escaped client certificate.
     *
     * @param sslClientEscapedCertHeader The escaped client certificate header name
     */
    public void setSslClientEscapedCertHeader(String sslClientEscapedCertHeader) {
        this.sslClientEscapedCertHeader = sslClientEscapedCertHeader;
    }

    /**
     * Returns the header name used to retrieve the cipher suite.
     *
     * @return The cipher header name
     */
    public String getSslCipherHeader() {
        return sslCipherHeader;
    }

    /**
     * Sets the header name used to retrieve the cipher suite.
     *
     * @param sslCipherHeader The cipher header name
     */
    public void setSslCipherHeader(String sslCipherHeader) {
        this.sslCipherHeader = sslCipherHeader;
    }

    /**
     * Returns the header name used to retrieve the SSL session ID.
     *
     * @return The session ID header name
     */
    public String getSslSessionIdHeader() {
        return sslSessionIdHeader;
    }

    /**
     * Sets the header name used to retrieve the SSL session ID.
     *
     * @param sslSessionIdHeader The session ID header name
     */
    public void setSslSessionIdHeader(String sslSessionIdHeader) {
        this.sslSessionIdHeader = sslSessionIdHeader;
    }

    /**
     * Returns the header name used to retrieve the cipher key size.
     *
     * @return The cipher key size header name
     */
    public String getSslCipherUserKeySizeHeader() {
        return sslCipherUserKeySizeHeader;
    }

    /**
     * Sets the header name used to retrieve the cipher key size.
     *
     * @param sslCipherUserKeySizeHeader The cipher key size header name
     */
    public void setSslCipherUserKeySizeHeader(String sslCipherUserKeySizeHeader) {
        this.sslCipherUserKeySizeHeader = sslCipherUserKeySizeHeader;
    }


    /**
     * Retrieves the value of the specified header from the request, handling null and "(null)" values.
     *
     * @param request The request object
     * @param header The header name to retrieve
     * @return The header value, or null if not present or equal to "(null)"
     */
    public String mygetHeader(Request request, String header) {
        String strcert0 = request.getHeader(header);
        if (strcert0 == null) {
            return null;
        }
        /* mod_header writes "(null)" when the ssl variable is no filled */
        if ("(null)".equals(strcert0)) {
            return null;
        }
        return strcert0;
    }


    @Override
    public void invoke(Request request, Response response) throws IOException, ServletException {
        /*
         * Known behaviours of reverse proxies that are handled by the processing below: - mod_header converts the '\n'
         * into ' ' - nginx converts the '\n' into multiple ' ' - nginx ssl_client_escaped_cert uses "uri component"
         * escaping, keeping only ALPHA, DIGIT, "-", ".", "_", "~"
         *
         * The code assumes that the trimmed header value starts with '-----BEGIN CERTIFICATE-----' and ends with
         * '-----END CERTIFICATE-----'.
         *
         * Note: As long as the BEGIN marker and the rest of the content are on separate lines, the CertificateFactory
         * is tolerant of any additional whitespace.
         */
        String headerValue;
        String headerEscapedValue = mygetHeader(request, sslClientEscapedCertHeader);
        if (headerEscapedValue != null) {
            headerValue = UDecoder.URLDecode(headerEscapedValue, null);
        } else {
            headerValue = mygetHeader(request, sslClientCertHeader);
        }
        if (headerValue != null) {
            headerValue = headerValue.trim();
            if (headerValue.length() > 27) {
                String body = headerValue.substring(27);
                String header = "-----BEGIN CERTIFICATE-----\n";
                String strcerts = header.concat(body);
                ByteArrayInputStream bais = new ByteArrayInputStream(strcerts.getBytes(StandardCharsets.ISO_8859_1));
                X509Certificate[] jsseCerts = null;
                String providerName = (String) request.getConnector().getProperty("clientCertProvider");
                try {
                    CertificateFactory cf;
                    if (providerName == null) {
                        cf = CertificateFactory.getInstance("X.509");
                    } else {
                        cf = CertificateFactory.getInstance("X.509", providerName);
                    }
                    X509Certificate cert = (X509Certificate) cf.generateCertificate(bais);
                    jsseCerts = new X509Certificate[1];
                    jsseCerts[0] = cert;
                } catch (java.security.cert.CertificateException e) {
                    log.warn(sm.getString("sslValve.certError", strcerts), e);
                } catch (NoSuchProviderException e) {
                    log.error(sm.getString("sslValve.invalidProvider", providerName), e);
                }
                request.setAttribute(Globals.CERTIFICATES_ATTR, jsseCerts);
            }
        }
        headerValue = mygetHeader(request, sslCipherHeader);
        if (headerValue != null) {
            request.setAttribute(Globals.CIPHER_SUITE_ATTR, headerValue);
        }
        headerValue = mygetHeader(request, sslSessionIdHeader);
        if (headerValue != null) {
            request.setAttribute(Globals.SSL_SESSION_ID_ATTR, headerValue);
        }
        headerValue = mygetHeader(request, sslCipherUserKeySizeHeader);
        if (headerValue != null) {
            try {
                request.setAttribute(Globals.KEY_SIZE_ATTR, Integer.valueOf(headerValue));
            } catch (NumberFormatException e) {
                log.warn(sm.getString("sslValve.invalidHeader", headerValue, sslCipherUserKeySizeHeader));
            }
        }
        getNext().invoke(request, response);
    }
}
