HTTP Digest Interceptor for Spring RestTemplate

HttpDigestAuthInterceptor.java

package com.blogtag.digest;

import java.io.IOException;
import java.util.Random;

import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpRequest;
import org.springframework.http.client.ClientHttpRequestExecution;
import org.springframework.http.client.ClientHttpRequestInterceptor;
import org.springframework.http.client.ClientHttpResponse;

public class AuthHttpDigestInterceptor implements ClientHttpRequestInterceptor {

	private final String REALM = "http-auth";
	private final String SEPARATOR = ", ";
	private final String QUOTE = "\"";
	private final String NONCE = Long.toString(new Random().nextLong(), 36);

	private HttpHeaders headers;

	private String username;
	private String password;

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

	@Override
	public ClientHttpResponse intercept(HttpRequest request, byte[] data, ClientHttpRequestExecution execution) throws IOException {
		headers = request.getHeaders();
		setAuthorizationHeader(request.getMethod().name(), username, password);
		return execution.execute(request, data);
	}

	private void setAuthorizationHeader(String method, String username, String password) {
		String digest1 = MD5.generate(username + ":" + REALM + ":" + password);
		String digest2 = MD5.generate(method + ":" + "/");
		String digest3 = MD5.generate(digest1 + ":" + NONCE + ":" + digest2);

		String value = "Digest " //
				+ "username=" + QUOTE + username + QUOTE + SEPARATOR //
				+ "realm=" + QUOTE + REALM + QUOTE + SEPARATOR //
				+ "nonce=" + QUOTE + NONCE + QUOTE + SEPARATOR //
				+ "uri=" + QUOTE + "/" + QUOTE + SEPARATOR //
				+ "response=" + QUOTE + digest3 + QUOTE;

		headers.add("authorization", value);
	}

}