如何使用HttpClient认证机制

转自：http://www.cnblogs.com/huqingyu/archive/2008/02/17/1071649.html
HttpClient三种不同的认证方案: Basic, Digest and NTLM. 这些方案可用于服务器或代理对客户端的认证，简称服务器认证或代理认证。
1．服务器认证(Server Authentication)
HttpClient处理服务器认证几乎是透明的，仅需要开发人员提供登录信息(login credentials)。登录信息保存在HttpState类的实例中，可以通过 setCredentials(String realm, Credentials cred)和getCredentials(String realm)来获取或设置。
HttpClient内建的自动认证，可以通过HttpMethod类的setDoAuthentication(boolean doAuthentication)方法关闭，而且这次关闭只影响HttpMethod当前的实例。

1.1抢先认证(Preemptive Authentication)
在这种模式时，HttpClient会主动将basic认证应答信息传给服务器，即使在某种情况下服务器可能返回认证失败的应答，这样做主要是为了减少连接的建立。使用该机制如下所示：
client.getParams().setAuthenticationPreemptive(true);

抢先认证模式也提供对于特定目标或代理的缺省认证。如果没有提供缺省的认证信息，则该模式会失效。
Credentials defaultcreds = new UsernamePasswordCredentials("username", "password");
client.getState().setCredentials(new AuthScope("myhost", 80, AuthScope.ANY_REALM), defaultcreds);

Httpclient实现的抢先认证遵循rfc2617.
A client SHOULD assume that all paths at or deeper than the depth of the last symbolic element in the path field of the Request-URI also are within the protection space specified by the Basic realm value of the current challenge. A client MAY preemptively send the corresponding Authorization header with requests for resources in that space without receipt of another challenge from the server. Similarly, when a client sends a request to a proxy, it may reuse a userid and password in the Proxy-Authorization header field without receiving another challenge from the proxy server.


1.2服务器认证的安全方面考虑
当需要与不被信任的站点或web应用通信时，应该谨慎使用缺省的认证机制。当启动(activate)抢先认证模式，或者认证中没有明确给出认证域，主机的HttpClient将使用缺省的认证机制去试图获得目标站点的授权。
如果你提供的认证信息是敏感的，你应该指定认证域。不推荐将认证域指定为AuthScope.ANY。（只有在debugging情况下，才使用）
// To be avoided unless in debug mode
Credentials defaultcreds = new UsernamePasswordCredentials("username", "password");
client.getState().setCredentials(AuthScope.ANY, defaultcreds);

2.代理认证(proxy authentication)
　　除了登录信息需单独存放以外，代理认证与服务器认证几乎一致。用 setProxyCredentials(String realm, Credentials cred)和 getProxyCredentials(String realm)设、取登录信息。
3.认证方案(authentication schemes)
3.1Basic
是HTTP中规定最早的也是最兼容的方案，遗憾的是也是最不安全的一个方案，因为它以明码传送用户名和密码。它要求一个UsernamePasswordCredentials实例，可以指定服务器端的访问空间或采用默认的登录信息。

3.2 Digest
是在HTTP1.1 中增加的一个方案，虽然不如Basic得到的软件支持多，但还是有广泛的使用。Digest方案比Basic方案安全得多，因它根本就不通过网络传送实际的密码，传送的是利用这个密码对从服务器传来的一个随机数(nonce)的加密串。
它要求一个UsernamePasswordCredentials实例，可以指定服务器端的访问空间或采用默认的登录信息。

3.3 NTLM
这是HttpClient支持的最复杂的认证协议。它Microsoft设计的一个私有协议，没有公开的规范说明。一开始由于设计的缺陷，NTLM的安全性比 Digest差，后来经过一个ServicePack补丁后，安全性则比较Digest高。
NTLM需要一个NTCredentials实例。 注意，由于NTLM不使用访问空间(realms)的概念，HttpClient利用服务器的域名作访问空间的名字。还需要注意，提供给 NTCredentials的用户名，不要用域名的前缀 - 如: "adrian" 是正确的，而 "DOMAIN\adrian" 则是错的。
NTLM认证的工作机制与basic和digest有很大的差别。这些差别一般由HttpClient处理，但理解这些差别有助避免在使用NTLM认证时出现错误。
[1] 从HttpClientAPI的角度来看，NTLM与其它认证方式一样的工作，差别是需要提供'NTCredentials'实例而不是'UsernamePasswordCredentials'(其实，前者只是扩展了后者)
[2] 对NTLM认证，访问空间是连接到的机器的域名，这对多域名主机会有一些麻烦。只有HttpClient连接中指定的域名才是认证用的域名。建议将realm设为null以使用默认的设置。
[3] NTLM只是认证了一个连接而不是一请求，所以每当一个新的连接建立就要进行一次认证，且在认证的过程中保持连接是非常重要的。 因此，NTLM不能同时用于代理认证和服务器认证，也不能用于HTTP1.0连接或服务器不支持持久连接(keep-alives)的情况。
关于NTLM认证机制更详细的研究，可参考http://davenport.sourceforge.net/ntlm.html 。

3.4选择认证
一些服务器支持多种认证方案。假设一次只能使用一种认证方案，HttpClient必须选择使用哪种。HttpClient选择是基于NTLM, Digest, Basic顺序的。
在具体情况下，可以更改该顺序。可通过参数'http.auth.scheme-priority'来实现，该参数值应该被存放在一个String类型的List中。选择优先级是按插入顺序确定的。
HttpClient client = new HttpClient();
List authPrefs = new ArrayList(2);
authPrefs.add(AuthPolicy.DIGEST);
authPrefs.add(AuthPolicy.BASIC);
// This will exclude the NTLM authentication scheme
client.getParams().setParameter(AuthPolicy.AUTH_SCHEME_PRIORITY, authPrefs);


3.5定制认证方案
HttpClient本身支持basic, digest, and NTLM这三种认证方案。同时，它也提供了加载额外定制的认证方案的功能（通过AuthScheme接口实现）。需要使用定制的认证方案，必须实现下面的步骤：
[1]实现AuthScheme接口。
[2]通过AuthPolicy.registerAuthScheme() 注册定制的AuthScheme。
[3]将定制的AuthScheme加入到AuthPolicy.AUTH_SCHEME_PRIORITY中。
4．示例
4.1Basic authentication
import org.apache.commons.httpclient.HttpClient;
import org.apache.commons.httpclient.UsernamePasswordCredentials;
import org.apache.commons.httpclient.auth.AuthScope;
import org.apache.commons.httpclient.methods.GetMethod;

/**
* A simple example that uses HttpClient to perform a GET using Basic
* Authentication. Can be run standalone without parameters.
*
* You need to have JSSE on your classpath for JDK prior to 1.4
*
* @author Michael Becke
*/
public class BasicAuthenticationExample {

    /**
     * Constructor for BasicAuthenticatonExample.
     */
    public BasicAuthenticationExample() {
        super();
    }

    public static void main(String[] args) throws Exception {
        HttpClient client = new HttpClient();

        // pass our credentials to HttpClient, they will only be used for
        // authenticating to servers with realm "realm" on the host
        // "www.verisign.com", to authenticate against
        // an arbitrary realm or host change the appropriate argument to null.
        client.getState().setCredentials(
            new AuthScope("www.verisign.com", 443, "realm"),
            new UsernamePasswordCredentials("username", "password")
        );

        // create a GET method that reads a file over HTTPS, we're assuming
        // that this file requires basic authentication using the realm above.
        GetMethod get = new GetMethod("https://www.verisign.com/products/index.html");

        // Tell the GET method to automatically handle authentication. The
        // method will use any appropriate credentials to handle basic
        // authentication requests.  Setting this value to false will cause
        // any request for authentication to return with a status of 401.
        // It will then be up to the client to handle the authentication.
        get.setDoAuthentication( true );

        try {         
            // execute the GET
            int status = client.executeMethod( get );

            // print the status and response
            System.out.println(status + "\n" + get.getResponseBodyAsString());

        } finally {
            // release any connection resources used by the method
            get.releaseConnection();
        }
    }
}


4.2 Alternate authentication
import java.util.ArrayList;
import java.util.List;

import org.apache.commons.httpclient.HttpClient;
import org.apache.commons.httpclient.UsernamePasswordCredentials;
import org.apache.commons.httpclient.auth.AuthPolicy;
import org.apache.commons.httpclient.auth.AuthScope;
import org.apache.commons.httpclient.methods.GetMethod;

/**
* <p>A simple example that uses alternate authentication scheme selection
* if several authentication challenges are returned.
* </p>
*
* <p>Per default HttpClient picks the authentication challenge in the following
*  order of preference: NTLM, Digest, Basic. In certain cases it may be desirable to
*  force the use of a weaker authentication scheme.
* </p>
*
* @author Oleg Kalnichevski
*/
public class AlternateAuthenticationExample {

    /**
     * Constructor for BasicAuthenticatonExample.
     */
    public AlternateAuthenticationExample() {
        super();
    }

    public static void main(String[] args) throws Exception {
        HttpClient client = new HttpClient();
        client.getState().setCredentials(
            new AuthScope("myhost", 80, "myrealm"),
            new UsernamePasswordCredentials("username", "password"));
        // Suppose the site supports several authetication schemes: NTLM and Basic
        // Basic authetication is considered inherently insecure. Hence, NTLM authentication
        // is used per default

        // This is to make HttpClient pick the Basic authentication scheme over NTLM & Digest
        List<String> authPrefs = new ArrayList<String>(3);
        authPrefs.add(AuthPolicy.BASIC);
        authPrefs.add(AuthPolicy.NTLM);
        authPrefs.add(AuthPolicy.DIGEST);
        client.getParams().setParameter(AuthPolicy.AUTH_SCHEME_PRIORITY, authPrefs);

        GetMethod httpget = new GetMethod("http://myhost/protected/auth-required.html");

        try {
            int status = client.executeMethod(httpget);
            // print the status and response
            System.out.println(status);
            System.out.println(httpget.getStatusLine());
            System.out.println(httpget.getResponseBodyAsString());
        } finally {
            // release any connection resources used by the method
            httpget.releaseConnection();
        }           
    }
}


4.3 Custom authentication
import java.util.ArrayList;
import java.util.Collection;

import org.apache.commons.httpclient.Credentials;
import org.apache.commons.httpclient.HttpMethod;
import org.apache.commons.httpclient.auth.AuthPolicy;
import org.apache.commons.httpclient.auth.AuthScheme;
import org.apache.commons.httpclient.auth.AuthenticationException;
import org.apache.commons.httpclient.auth.MalformedChallengeException;
import org.apache.commons.httpclient.params.DefaultHttpParams;
import org.apache.commons.httpclient.params.HttpParams;

/**
* A simple custom AuthScheme example.  The included auth scheme is meant
* for demonstration purposes only.  It does not actually implement a usable
* authentication method.
*/
public class CustomAuthenticationExample {

    @SuppressWarnings("unchecked")
    public static void main(String[] args) {
       
        // register the auth scheme
        AuthPolicy.registerAuthScheme(SecretAuthScheme.NAME, SecretAuthScheme.class);

        // include the scheme in the AuthPolicy.AUTH_SCHEME_PRIORITY preference,
        // this can be done on a per-client or per-method basis but we'll do it
        // globally for this example
        HttpParams params = DefaultHttpParams.getDefaultParams();       
        ArrayList<String> schemes = new ArrayList<String>();
        schemes.add(SecretAuthScheme.NAME);
        schemes.addAll( (Collection) params.getParameter(AuthPolicy.AUTH_SCHEME_PRIORITY));
        params.setParameter(AuthPolicy.AUTH_SCHEME_PRIORITY, schemes);
       
        // now that our scheme has been registered we can execute methods against
        // servers that require "Secret" authentication...
    }
   
    /**
     * A custom auth scheme that just uses "Open Sesame" as the authentication
     * string.
     */
    private class SecretAuthScheme implements AuthScheme {

        public static final String NAME = "Secret";

        public SecretAuthScheme() {
            // All auth schemes must have a no arg constructor.
        }
        public String authenticate(Credentials credentials, HttpMethod method)
            throws AuthenticationException {
            return "Open Sesame";
        }
        public String authenticate(Credentials credentials, String method,
                String uri) throws AuthenticationException {
            return "Open Sesame";
        }
        public String getID() {
            return NAME;
        }
        public String getParameter(String name) {
            // this scheme does not use parameters, see RFC2617Scheme for an example
            return null;
        }
        public String getRealm() {
            // this scheme does not use realms
            return null;
        }
        public String getSchemeName() {
            return NAME;
        }
        public boolean isConnectionBased() {
            return false;
        }
        public void processChallenge(String challenge)
                throws MalformedChallengeException {
            // Nothing to do here, this is not a challenge based
            // auth scheme.  See NTLMScheme for a good example.
        }
        public boolean isComplete() {
            // again we're not a challenge based scheme so this is always true
            return true;
        }
    }
}


4.4 Interactive authentication
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

import org.apache.commons.httpclient.Credentials;
import org.apache.commons.httpclient.HttpClient;
import org.apache.commons.httpclient.NTCredentials;
import org.apache.commons.httpclient.UsernamePasswordCredentials;
import org.apache.commons.httpclient.auth.AuthScheme;
import org.apache.commons.httpclient.auth.CredentialsNotAvailableException;
import org.apache.commons.httpclient.auth.CredentialsProvider;
import org.apache.commons.httpclient.auth.NTLMScheme;
import org.apache.commons.httpclient.auth.RFC2617Scheme;
import org.apache.commons.httpclient.methods.GetMethod;

/**
* A simple example that uses HttpClient to perform interactive
* authentication.
*
* @author Oleg Kalnichevski
*/
public class InteractiveAuthenticationExample {

    /**
     * Constructor for InteractiveAuthenticationExample.
     */
    public InteractiveAuthenticationExample() {
        super();
    }

    public static void main(String[] args) throws Exception {

        InteractiveAuthenticationExample demo = new InteractiveAuthenticationExample();
        demo.doDemo();
    }
   
    private void doDemo() throws IOException {

        HttpClient client = new HttpClient();
        client.getParams().setParameter(
            CredentialsProvider.PROVIDER, new ConsoleAuthPrompter());
        GetMethod httpget = new GetMethod("http://target-host/requires-auth.html");
        httpget.setDoAuthentication(true);
        try {
            // execute the GET
            int status = client.executeMethod(httpget);
            // print the status and response
            System.out.println(status);
            System.out.println(httpget.getStatusLine().toString());
            System.out.println(httpget.getResponseBodyAsString());
        } finally {
            // release any connection resources used by the method
            httpget.releaseConnection();
        }
    }

    public class ConsoleAuthPrompter implements CredentialsProvider {

        private BufferedReader in = null;
        public ConsoleAuthPrompter() {
            super();
            this.in = new BufferedReader(new InputStreamReader(System.in));
        }
       
        private String readConsole() throws IOException {
            return this.in.readLine();
        }
       
        public Credentials getCredentials(
            final AuthScheme authscheme,
            final String host,
            int port,
            boolean proxy)
            throws CredentialsNotAvailableException
        {
            if (authscheme == null) {
                return null;
            }
            try{
                if (authscheme instanceof NTLMScheme) {
                    System.out.println(host + ":" + port + " requires Windows authentication");
                    System.out.print("Enter domain: ");
                    String domain = readConsole();  
                    System.out.print("Enter username: ");
                    String user = readConsole();  
                    System.out.print("Enter password: ");
                    String password = readConsole();
                    return new NTCredentials(user, password, host, domain);   
                } else
                if (authscheme instanceof RFC2617Scheme) {
                    System.out.println(host + ":" + port + " requires authentication with the realm '"
                        + authscheme.getRealm() + "'");
                    System.out.print("Enter username: ");
                    String user = readConsole();  
                    System.out.print("Enter password: ");
                    String password = readConsole();
                    return new UsernamePasswordCredentials(user, password);   
                } else {
                    throw new CredentialsNotAvailableException("Unsupported authentication scheme: " +
                        authscheme.getSchemeName());
                }
            } catch (IOException e) {
                throw new CredentialsNotAvailableException(e.getMessage(), e);
            }
        }
    }
}