package pop3srvr;

public class App {

    public static void main(String[] args) {
        new POP3Server().run();
    }

}

////////////////////////////////////////////////////////////////////////////////////////////////////////



package pop3srvr;

import sun.misc.BASE64Decoder;
import sun.misc.BASE64Encoder;

import java.io.BufferedOutputStream;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.ServerSocket;
import java.net.Socket;

public class POP3Server implements Runnable {
    // pop3 port number
    public static final int PORT = 11000;

    private ServerSocket fServerSocket = null;
    private Socket clientSocket = null;

    private BASE64Decoder decoder = new BASE64Decoder();
    private BASE64Encoder encoder = new BASE64Encoder();

    private final byte[] OK_MESSAGE = "+OK\n".getBytes();

    //Open server socket
    public POP3Server() {
        try {
            fServerSocket = new ServerSocket(PORT);
            System.out.println("Server started.");
        } catch (IOException e) {
            System.err.println("error:");
            e.printStackTrace();
            System.exit(1);
        }
    }

    public void run() {

        BufferedOutputStream pop3out;
        BufferedReader pop3in;
        while (true) {
            try {
                //waiting for incoming connections
                clientSocket = fServerSocket.accept();

                //assigning socket streams
                pop3out = new BufferedOutputStream(clientSocket.getOutputStream());
                pop3in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));

                //do initial response
                pop3out.write(OK_MESSAGE);
                pop3out.flush();

                //request mwssage
                String message;

                //while input stream not closed
                while ((message = pop3in.readLine()) != null) {

                    // parsing is here
                    System.out.println("Request: " + message);
                    if (message.equals("CAPA")) {
                        pop3out.write("+OK Capability list follows\nSASL CRAM-MD5 PLAIN\n.\n".getBytes());
                    } else if (message.startsWith("AUTH")) {
                        pop3out.write(OK_MESSAGE);
                        pop3out.flush();
                        if (message.endsWith("PLAIN")) {
                            byte[] authdata = decode(pop3in.readLine().getBytes());

                            // plain authentication
                            byte[] response = authenticate(authdata, "PLAIN");
                            if (response != null) {
                                pop3out.write(OK_MESSAGE);
                            } else {
                                pop3out.write("-ERR\n".getBytes());
                            }
                        } else if (message.endsWith("CRAM-MD5")) {
                            // it's not working yet
                            byte[] data = pop3in.readLine().getBytes();

                            System.out.println("Data1: " + new String(data));

                            byte[] response = authenticate(data, "CRAM-MD5");
                            pop3out.write(response);
                            pop3out.write('\n');
                            pop3out.flush();
                            pop3out.write(OK_MESSAGE);
                            pop3out.flush();


                            byte[] anotherdata = pop3in.readLine().getBytes();
                            System.out.println("Data1: " + new String(anotherdata));

                            if (response != null) {
                                pop3out.write(OK_MESSAGE);
                            } else {
                                pop3out.write("-ERR\n".getBytes());
                            }
                            pop3out.write(OK_MESSAGE);
                        }
                    } else {
                        pop3out.write(OK_MESSAGE);
                    }
                    pop3out.flush();
                }

            } catch (IOException e) {
                System.err.println("error:");
                e.printStackTrace();
            }
        }
    }

    public byte[] authenticate(byte[] request, String method) {
        if (request == null) {
            return OK_MESSAGE;
        }

        return SaslAuthenticator.instance.auth(request, method);
    }

    public byte[] encode(byte[] data) {
        return encoder.encode(data).getBytes();
    }

    public byte[] decode(byte[] data) {
        try {
            return decoder.decodeBuffer(new String(data));
        } catch (IOException e) {
            return null;
        }
    }


    //close session
    public void quit() {
        try {
            clientSocket.close();
        } catch (IOException e) {
            System.err.println("error:");
            e.printStackTrace();
        }
    }
}

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////




package pop3srvr;

import pop3srvr.provider.ExternalValidationCallback;
import pop3srvr.provider.MySecurityProvider;

import javax.security.auth.callback.Callback;
import javax.security.auth.callback.CallbackHandler;
import javax.security.auth.callback.NameCallback;
import javax.security.auth.callback.PasswordCallback;
import javax.security.auth.callback.UnsupportedCallbackException;
import javax.security.sasl.AuthorizeCallback;
import javax.security.sasl.Sasl;
import javax.security.sasl.SaslException;
import javax.security.sasl.SaslServer;
import java.io.IOException;
import java.security.Security;
import java.util.HashMap;
import java.util.Map;

public class SaslAuthenticator {

    public static final SaslAuthenticator instance = new SaslAuthenticator();

    public static final String PLAIN = "PLAIN";
    public static final String MD5 = "CRAM-MD5";
    private final Map<String,String> authorizedUsers = new HashMap<String,String>();

    private Map<String, SaslServer> saslServers = new HashMap<String, SaslServer>();

    private SaslAuthenticator() {
        Security.addProvider(new MySecurityProvider());

        authorizedUsers.put("energy", "mypass");
        authorizedUsers.put("user", "userpass");

        CallbackHandler md5CallbackHandler = new CallbackHandler() {

            public void handle(Callback[] cbs) throws IOException, UnsupportedCallbackException {
                String user = null;
                for (Callback cb : cbs) {
                    if (cb instanceof AuthorizeCallback) {

                        System.out.println("Server - AuthorizeCallback");

                        AuthorizeCallback ac = (AuthorizeCallback) cb;
                        ac.setAuthorized(true);

                    } else if (cb instanceof NameCallback) {

                        System.out.println("Server - NameCallback");

                        NameCallback nc = (NameCallback) cb;
                        if (authorizedUsers.containsKey(nc.getDefaultName())) {
                            user = nc.getDefaultName();
                            nc.setName(nc.getDefaultName());
                        }
                    } else if (cb instanceof PasswordCallback) {
                        System.out.println("Server - PasswordCallback");

                        PasswordCallback pc = (PasswordCallback) cb;
                        if (user != null) {
                            pc.setPassword(authorizedUsers.get(user).toCharArray());
                        }
                    }
                }
            }
        };

        CallbackHandler plainCallbackHandler = new CallbackHandler() {
            public void handle(Callback[] callbacks) throws IOException, UnsupportedCallbackException {
                for (Callback cb : callbacks) {
                    if (cb instanceof ExternalValidationCallback) {
                        ExternalValidationCallback evc = (ExternalValidationCallback) cb;
                        final String username = evc.getUsername().subSequence(1, evc.getUsername().length()).toString();

                        if (authorizedUsers.containsKey(username) && authorizedUsers.get(username).equals(evc.getPassword())) {
                            evc.setValidated(true);
                        } else {
                            evc.setValidated(false);
                        }
                    } else if (cb instanceof AuthorizeCallback) {
                        AuthorizeCallback ac = (AuthorizeCallback) cb;

                        ac.setAuthorized(true);
                    } else {
                        throw new UnsupportedCallbackException(cb, "Unrecognized Callback");
                    }
                }
            }
        };

        try {
            saslServers.put(PLAIN, Sasl.createSaslServer(PLAIN, "myProtocol", "local", null, plainCallbackHandler));
            saslServers.put(MD5, Sasl.createSaslServer(MD5, "myProtocol", "local", null, md5CallbackHandler));
        } catch (SaslException e) {
            e.printStackTrace();
        }
    }

    public byte[] auth(byte[] data, final String method) {

        byte[] challenge = null;
        //byte[] response;

        try {
            String mechanism = null;
            if (method.equals(PLAIN)) {
                mechanism = PLAIN;
                saslServers.get(PLAIN).evaluateResponse(data);
            } else if (method.equals(MD5)) {
                mechanism = MD5;
                challenge = saslServers.get(MD5).evaluateResponse(new byte[0]);
                System.out.println("Server: " + new String(challenge));
                return challenge;
            }

            if (saslServers.get(mechanism).isComplete()) {
                System.out.println("Authentication successful.");
                return new byte[0];
            }
        } catch (SaslException e) {
            System.out.println("Authentication failed.");
        }
        return null;
    }

}


////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////


package pop3srvr.provider;

import javax.security.auth.callback.Callback;

public class ExternalValidationCallback implements Callback {

    private String username;
    private String password;
    private boolean validated = false;

    public ExternalValidationCallback(String username, String password) {
        this.username = username;
        this.password = password;
    }

    public String getPassword() {
        return password;
    }

    public String getUsername() {
        return username;
    }

    public boolean isValidated() {
        return validated;
    }

    public void setValidated(boolean validated) {
        this.validated = validated;
    }
}



package pop3srvr.provider;

import java.security.Provider;

public final class MySecurityProvider extends Provider {

    public MySecurityProvider() {
        super("My Provider", 1.0, "Simple sasl plain provider");
        put("SaslServerFactory.PLAIN", "pop3srvr.provider.PlainSaslServerFactory");
    }

}




package pop3srvr.provider;

import javax.security.auth.callback.Callback;
import javax.security.auth.callback.CallbackHandler;
import javax.security.auth.callback.UnsupportedCallbackException;
import javax.security.sasl.AuthorizeCallback;
import javax.security.sasl.SaslException;
import javax.security.sasl.SaslServer;
import java.io.IOException;
import java.io.UnsupportedEncodingException;

/**
 * Simple sasl server to decode a
 *
 * @author toaster
 */
public class PlainSaslServer implements SaslServer {

    public boolean complete = false;
    private String authID = null;
    private CallbackHandler cbh;

    PlainSaslServer(CallbackHandler cbh) {
        this.cbh = cbh;
    }

    public String getMechanismName() {
        return "PLAIN".intern(); //SaslConstants.SASL_SERVICE;
    }

    public byte[] evaluateResponse(byte[] response) throws SaslException {
        String authnID = null;
        String authzID = null;
        String password = null;

        // Decode response as per rfc4616.txt
//       The formal grammar for the client message using Augmented BNF [ABNF]
//       follows.
//
//       message   = [authzid] UTF8NUL authcid UTF8NUL passwd
//       authcid   = 1*SAFE ; MUST accept up to 255 octets
//       authzid   = 1*SAFE ; MUST accept up to 255 octets
//       passwd    = 1*SAFE ; MUST accept up to 255 octets
//       UTF8NUL   = %x00 ; UTF-8 encoded NUL character
//
//       SAFE      = UTF1 / UTF2 / UTF3 / UTF4
//                   ;; any UTF-8 encoded Unicode character except NUL
//
//       UTF1      = %x01-7F ;; except NUL
//       UTF2      = %xC2-DF UTF0
//       UTF3      = %xE0 %xA0-BF UTF0 / %xE1-EC 2(UTF0) /
//                   %xED %x80-9F UTF0 / %xEE-EF 2(UTF0)
//       UTF4      = %xF0 %x90-BF 2(UTF0) / %xF1-F3 3(UTF0) /
//                   %xF4 %x80-8F 2(UTF0)
//       UTF0      = %x80-BF

        int start = 0;
        int end = 0;
        int elementIdx = 0;

        try {
            for (byte b : response) {
                if (b == '\u0000') {
                    // empty string, only authzid allows this
                    if (end - start == 0) {
                        if (elementIdx != 0) {
                            throw new SaslException("null auth data");
                        }

                    } // data, wa-hoo
                    else {
                        String element = new String(response, start, end - start, "UTF-8");
                        start = end + 1;

                        switch (elementIdx) {
                            case 0:
                                authzID = element;
                                break;
                            case 1:
                                authnID = element;
                                break;
                            default:
                                throw new SaslException("Unexpected data in packet");
                        }
                    }
                    elementIdx++;

                }
                end++;
            }

            if (start == end) {
                throw new SaslException("null auth data");
            }

            password = new String(response, start, end - start, "UTF-8");


        } catch (UnsupportedEncodingException e) {
            throw new SaslException("utf-8 encoding");
        }


        ExternalValidationCallback evc = new ExternalValidationCallback(authnID, password);
        AuthorizeCallback ac = new AuthorizeCallback(authnID, authzID);

        Callback[] cbList = new Callback[2];

        cbList[0] = evc;
        cbList[1] = ac;

        try {
            if (password == null || authnID == null) {
                throw new SaslException("null auth data");
            }

            cbh.handle(cbList);
            if (!evc.isValidated()) {
                throw new SaslException("cannot validate password");
            }

            if (!ac.isAuthorized()) {
                throw new SaslException("user not authorized");
            }

            complete = true;
            return null;

        } catch (UnsupportedCallbackException ex) {
            throw new SaslException("unsupported callback", ex);

        } catch (IOException e) {
            if (e instanceof SaslException) {
                throw (SaslException) e;
            }
            throw new SaslException("Callback error", e);
        }

    }

    public boolean isComplete() {
        return complete;
    }

    public String getAuthorizationID() {
        if (!complete) {
            throw new IllegalStateException("not complete");
        }
        return authID;
    }

    public byte[] unwrap(byte[] incoming, int offset, int len) {
        if (!complete) {
            throw new IllegalStateException("not complete");
        }
        final byte[] result = new byte[len];
        System.arraycopy(incoming, offset, result, 0, len);
        return result;

    }

    public byte[] wrap(byte[] outgoing, int offset, int len) {
        if (!complete) {
            throw new IllegalStateException("not complete");
        }

        final byte[] result = new byte[len];
        System.arraycopy(outgoing, offset, result, 0, len);
        return result;

    }

    public Object getNegotiatedProperty(String propName) {
        return null;
    }

    public void dispose() throws SaslException {
    }
}




package pop3srvr.provider;

import javax.security.auth.callback.CallbackHandler;
import javax.security.sasl.Sasl;
import javax.security.sasl.SaslException;
import javax.security.sasl.SaslServer;
import javax.security.sasl.SaslServerFactory;
import java.util.Map;

public class PlainSaslServerFactory implements SaslServerFactory {

    private static String[] mechanisms = {"PLAIN".intern()};

    public SaslServer createSaslServer(String mechanism, String protocol,
                                       String serverName,
                                       Map props, CallbackHandler cbh) throws SaslException {

        if (!mechanisms[0].equals(mechanism) || cbh == null)
            return null;
        return new PlainSaslServer(cbh);

    }

    public String[] getMechanismNames(Map props) {
        if ("true".equals(props.get(Sasl.POLICY_NOPLAINTEXT)))
            return new String[0];
        return mechanisms;
    }
}