使用搶佔式基本身份驗證與 RestTemplate 和 HttpClient

搶先式基本身份驗證是在伺服器回覆 401 響應請求之前傳送 http 基本身份驗證憑據（使用者名稱和密碼） 的做法。這可以在使用已知需要基本身份驗證的 REST api 時儲存請求往返。

如 Spring 文件中所述， Apache HttpClient可以用作底層實現，通過使用 HttpComponentsClientHttpRequestFactory 來建立 HTTP 請求。HttpClient 可以配置為執行搶佔式基本身份驗證 。

以下類擴充套件 HttpComponentsClientHttpRequestFactory 以提供搶先式基本身份驗證。

/**
 * {@link HttpComponentsClientHttpRequestFactory} with preemptive basic
 * authentication to avoid the unnecessary first 401 response asking for
 * credentials.
 * <p>
 * Only preemptively sends the given credentials to the given host and
 * optionally to its subdomains. Matching subdomains can be useful for APIs
 * using multiple subdomains which are not always known in advance.
 * <p>
 * Other configurations of the {@link HttpClient} are not modified (e.g. the
 * default credentials provider).
 */
public class PreAuthHttpComponentsClientHttpRequestFactory extends HttpComponentsClientHttpRequestFactory {

    private String hostName;
    private boolean matchSubDomains;
    private Credentials credentials;

    /**
     * @param httpClient
     *            client
     * @param hostName
     *            host name
     * @param matchSubDomains
     *            whether to match the host's subdomains
     * @param userName
     *            basic authentication user name
     * @param password
     *            basic authentication password
     */
    public PreAuthHttpComponentsClientHttpRequestFactory(HttpClient httpClient, String hostName,
            boolean matchSubDomains, String userName, String password) {
        super(httpClient);
        this.hostName = hostName;
        this.matchSubDomains = matchSubDomains;
        credentials = new UsernamePasswordCredentials(userName, password);
    }

    @Override
    protected HttpContext createHttpContext(HttpMethod httpMethod, URI uri) {
        // Add AuthCache to the execution context
        HttpClientContext context = HttpClientContext.create();
        context.setCredentialsProvider(new PreAuthCredentialsProvider());
        context.setAuthCache(new PreAuthAuthCache());
        return context;
    }

    /**
     * @param host
     *            host name
     * @return whether the configured credentials should be used for the given
     *         host
     */
    protected boolean hostNameMatches(String host) {
        return host.equals(hostName) || (matchSubDomains && host.endsWith("." + hostName));
    }

    private class PreAuthCredentialsProvider extends BasicCredentialsProvider {
        @Override
        public Credentials getCredentials(AuthScope authscope) {
            if (hostNameMatches(authscope.getHost())) {
                // Simulate a basic authenticationcredentials entry in the
                // credentials provider.
                return credentials;
            }
            return super.getCredentials(authscope);
        }
    }

    private class PreAuthAuthCache extends BasicAuthCache {
        @Override
        public AuthScheme get(HttpHost host) {
            if (hostNameMatches(host.getHostName())) {
                // Simulate a cache entry for this host. This instructs
                // HttpClient to use basic authentication for this host.
                return new BasicScheme();
            }
            return super.get(host);
        }
    }
}

這可以使用如下：

HttpClientBuilder builder = HttpClientBuilder.create();
ClientHttpRequestFactory requestFactory =
    new PreAuthHttpComponentsClientHttpRequestFactory(builder.build(),
        "api.some-host.com", true, "api", "my-key");
RestTemplate restTemplate = new RestTemplate(requestFactory);