Java CookBook Learning Day4th--HTTP (by Tim O'Brien)

本文详细介绍了HTTP基本认证和NTLM认证的原理、实现方法及注意事项，包括如何使用Apache HttpClient库进行认证操作，以及如何配置客户端以预授权认证信息，避免因服务器响应401未授权错误而产生的额外请求。

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1.9. Basic Authentication

1.9.1. Problem

You need to access information protected by HTTP Basic Authentication.

1.9.2.Solution

Create a UsernamePasswordCredentials object with a username and password. Add this Credentials object to the instance of HttpState associated with an HttpClient object. HttpClient will attempt to execute a message, and the server will response with 401 response code;HttpClient will then retry the request with the appropriate Authorization header. The following example uses a UsernamePasswordCredentials object to access a protected resource:

import org.apache.commons.httpclient.Credentials;
import org.apache.commons.httpclient.HttpClient;
import org.apache.commons.httpclient.Exception;
import org.apache.commons.httpclient.HttpMethod;
import org.apache.commons.httpclient.UsernamePasswordCredentials;
import org.apache.commons.httpclient.GetMethod;
HttpClient client = new HttpClient( );
HttpState state = client.getState( );
//Set credentials on the client
Credentials credentials = new UsernamePasswordCredentials("testuser","crazypass");
state.setCredentials( null, null, credentials);
String url = "http://www.discursive.com/jccook/auth/";
HttpMethod method = new GetMethod( url );
client.executeMethod( method);
String response = method.getReponseBodyAsString( );
method.releaseConnection( );

This example executes a GetMethod, the server requests credentials, and the credentials are sent to the server. The final
response is:

<html>
<head>
<title>Secure JCCook Example</title>
</head>
<body>
<h1>Hello Secure World!</h1>
</body>
</html>

1.9.3.Discussion

The previous example added a UsernamePasswordCredentials object to the HttpState with a null authentication realm and null host; this makes the supplied UsernamePasswordCredentials object the default instance to use for all authentication realms and hosts. The requests and response created by this example demonstrate the inner-workings of HttpClient, which sent the following request when the GetMethod was executed:

GET /jccook/auth/ HTTP/1.1
User-Agent: Jakarta Commons-HttpClient/3.0final
Host: www.discursive.com

The server then responds with a 401 response code, telling the client that authorization is required. The WWW-Authenticate header specifies that the server is expecting Basic authentication, and the authentication realm is jccook realm:

HTTP/1.1 401 Authorization Required  
Date: Fri, 14 May 2004 20:40:59 GMT
Server: Apache/2.0.48 (Fedora)
WWW-Authenticate: Basic realm="jccook realm"
Content-Length: 487
Content-Type: text/html; charset=iso-8859-1
DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
<html><head>
title>401 Authorization Required</title>
</head><body>
.... error message

The server did not return the information needed, and another request needs to be made, sending the credentials in an Authorization request header. Since the initial request was made with HTTP/1.1, the connection is not closed after the response, and a second request will be sent over the same connection. This second request is the same as the first request except for an Authorization header. HttpClient looked at the associated HttpState object and located the appropriate Credentials object to use to create the Authorization header:

GET /jccook/auth/ HTTP/1.1
User-Agent: Jakarta Commons-HttpClient/3.0final
Host: www.discursive.com
Authorization: Basic dGVzdHVzZXI6Y3JhenlwYXNz

Finally, the server replies with a 200 response code and the content of the requested resource:

HTTP/1.1 200 OK
Date: Fri, 14 May 2004 20:40:59 GMT
Server: Apache/2.0.48 (Fedora)
Last-Modified: Wed, 05 May 2004 02:51:59 GMT
ETag: "a06d2-76-829811c0"
Accept-Ranges: bytes
Content-Length: 118
Content-Type: text/html; charset=UTF-8
<html>
<head>
<title>Secure JCCook Example</title>
</head>
<body>
<h1>Hello Secure World!</h1>
</body>
</html>

HttpClient waits for the server to send back a 401 response code before sending the appropriate credentials. If you are accessing a resource, which is known to be protected by authentication, you can configure the HttpState object to send credentials preemptively, obviating the need for the client to react to a 401 response code. In other words, the Authorization header is supplied in the initial request. To configure HttpClient to send credentials preemptively, retrieve an HttpClientParams object form HttpClient via getParams( ) method, and call setAuthenticationPreemptive(true) as follows:

HttpClientParams params = client.getParams( );
params.setAuthenticationPreemptive( true);

Warning: Basic authentication involves sending an unencrypted password in the request. The value of the Authentication header in the request is simply testuser:crazypass sent through a Base64 encoding utility. If you are working on a system that uses Basic authentication, make sure that any system that performs authentication does so over SSL；otherwise, your password will fall into the wrong hands.

1.10. NTLM Authentication

1.10.1. Problem

You need to access a resource that is protected by Microsoft's NTLM authentication protocol.

1.10.2. Solution

Create an instance of NTCredentials with a username, password, host, and domain,and setCredentials( ) on the HttpState associated with an instance of HttpClient. The following example demonstrates the use of NTCredentials to access a resource on host test.windowsmachine.com, which is on the domain TESTDOM:

import org.apache.commons.httpclient.Credentials;
import org.apache.commons.httpclient.HttpClient;
import org.apache.commons.httpclient.HttpState;
import org.apache.commons.httpclient.HttpException;
import org.apache.commons.httpclient.HttpMethod;
import org.apache.commons.httpclient.NTCredentials;
import org.apache.commons.httpclient.methods.GetMethod;
HttpClient client = new HttpClient( );
//set credentials on the client
Credentials credentials = new NTCredentials (“testuser", ”crazypass","homecomputer","TESTDOM");
HttpState state = client.getState( )；
state( ).setCredentials(null,null,credentials);
String url = "http://webmail.domain.biz/exchange/";
HttpMethod method = new GetMethod ( url );
client.executeMethod( method);
String response = method.getResponseBodyAsString( );
System.out.println( response);
method.releaseConnection( );

1.10.3. Discussion

The parameters to the constructor of NTCredentials are the username, the password, a hostname, and a domain. The hostname is the name of the machine making the request, and in this case, the third parameters is homecomputer. When this Credential object is set in the HttpState object, the first two parameter specify the authentication realm and the host to apply a Credential object to. The previous example sets both the authentication realm and the host to null; this makes the NTCredentials object the default Credentials to use if there is no realm or host specified. If we were using one instance of HttpClient to connect to two different hosts with two different NTCredentials objects, both Credentials objects could be added to HttpState with the following code:

HttpClient client = new HttpClient( );
Credentials credentials1 = new NTCredentials( "testuser", "crazypass","homecomputer", "TESTDOM" );
Credentials credentials2 =new NTCredentials( "anotheruser", "password2","homecomputer", "DIFFERENT_DOMAIN" );
state( ).setCredentials( null, "webmail.domain.biz", credentials1 );
state( ).setCredentials( null, "silly-iis-server.lame.net", credentials2 );
// Execute a request which uses credentials1
String url = "http://webmail.domain.biz/exchange/";
HttpMethod method = new GetMethod( url );
client.executeMethod( method );
// Execute a request which uses credentials2
String url2 = "http://silly-iis-server.lame.net/test/";
HttpMethod method2 = new GetMethod( url2 );
client.executeMethod( method2 );

The host webmail.domain.biz tries to authenticate the first request against the TESTDOM domain, and the silly-iis-server.lame.net host tries to authenticate the second request against the DIFFERENT_DOMAIN domain. Since the HttpState is configured with two separate Credentials objects for different hosts, both requests are successfully authenticated.