HTTP Digest Auth for Android (incomplete and probably hackable, but works!)

HttpDigestAuth.java

import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.net.HttpURLConnection;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.HashMap;

import com.google.common.base.CharMatcher;
import com.google.common.base.Joiner;
import com.google.common.base.Splitter;
import com.google.common.collect.Iterables;
import com.google.common.collect.Maps;


public class HttpDigestAuth
{
	public HttpURLConnection tryAuth(HttpURLConnection connection, String username, String password)
		throws IOException
	{
		int responseCode = connection.getResponseCode();
		if(responseCode == HttpURLConnection.HTTP_UNAUTHORIZED){
			connection = tryDigestAuthentication(connection, username, password);
			if(connection == null){
				throw new AuthenticationException();
			}
		}
		return connection;
	}
	
	public static HttpURLConnection tryDigestAuthentication(HttpURLConnection input, String username, String password)
	{
		String auth = input.getHeaderField("WWW-Authenticate");
		if(auth == null || !auth.startsWith("Digest ")){
			return null;
		}
		final HashMap<String, String> authFields = splitAuthFields(auth.substring(7));
		
		MessageDigest md5 = null;
		try{
			md5 = MessageDigest.getInstance("MD5");
		}
		catch(NoSuchAlgorithmException e){
			return null;
		}
		
		Joiner colonJoiner = Joiner.on(':');
		
		String HA1 = null;
		try{
			md5.reset();
			String ha1str = colonJoiner.join(username, 
				authFields.get("realm"), password);
			md5.update(ha1str.getBytes("ISO-8859-1"));
			byte[] ha1bytes = md5.digest();
			HA1 = bytesToHexString(ha1bytes);
		}
		catch(UnsupportedEncodingException e){
			return null;
		}
		
		String HA2 = null;
		try{
			md5.reset();
			String ha2str = colonJoiner.join(input.getRequestMethod(),
				input.getURL().getPath());
			md5.update(ha2str.getBytes("ISO-8859-1"));
			HA2 = bytesToHexString(md5.digest());
		}
		catch(UnsupportedEncodingException e){
			return null;
		}
		
		String HA3 = null;
		try{
			md5.reset();
			String ha3str = colonJoiner.join(HA1, authFields.get("nonce"), HA2);
			md5.update(ha3str.getBytes("ISO-8859-1"));
			HA3 = bytesToHexString(md5.digest());
		}
		catch(UnsupportedEncodingException e){
			return null;
		}
		
		StringBuilder sb = new StringBuilder(128);
		sb.append("Digest ");
		sb.append("username").append("=\"").append(username                ).append("\",");
		sb.append("realm"   ).append("=\"").append(authFields.get("realm") ).append("\",");
		sb.append("nonce"   ).append("=\"").append(authFields.get("nonce") ).append("\",");
		sb.append("uri"     ).append("=\"").append(input.getURL().getPath()).append("\",");
		//sb.append("qop"     ).append('='  ).append("auth"                  ).append(",");
		sb.append("response").append("=\"").append(HA3                     ).append("\"");
		
		try{
			final HttpURLConnection result = (HttpURLConnection)input.getURL().openConnection();
			result.addRequestProperty("Authorization", sb.toString());
			return result;
		}
		catch(IOException e){
			return null;
		}
	}
	
	private static HashMap<String, String> splitAuthFields(String authString)
	{
		final HashMap<String, String> fields = Maps.newHashMap();
		final CharMatcher trimmer = CharMatcher.anyOf("\"\t ");
		final Splitter commas = Splitter.on(',').trimResults().omitEmptyStrings();
		final Splitter equals = Splitter.on('=').trimResults(trimmer).limit(2);
		String[] valuePair;
		for(String keyPair : commas.split(authString)){
			valuePair = Iterables.toArray(equals.split(keyPair), String.class);
			fields.put(valuePair[0], valuePair[1]);
		}
		return fields;
	}
	
	private static final String HEX_LOOKUP = "0123456789abcdef";
	private static String bytesToHexString(byte[] bytes)
	{
		StringBuilder sb = new StringBuilder(bytes.length * 2);
		for(int i = 0; i < bytes.length; i++){
			sb.append(HEX_LOOKUP.charAt((bytes[i] & 0xF0) >> 4));
			sb.append(HEX_LOOKUP.charAt((bytes[i] & 0x0F) >> 0));
		}
		return sb.toString();
	}
	
	public static class AuthenticationException extends IOException
	{
		private static final long serialVersionUID = 1L;
		public AuthenticationException()
		{
			super("Problems authenticating");
		}
	}
}