Add support for proxies requiing authentication

sdk/lib/io/http.dart

Index: sdk/lib/io/http.dart
diff --git a/sdk/lib/io/http.dart b/sdk/lib/io/http.dart
index 72fd67c5b4ee5ed191d0b11d70af7747ecf2b304..5ec79e248ad3934456395a7df6b9e5c0419b8782 100644
--- a/sdk/lib/io/http.dart
+++ b/sdk/lib/io/http.dart
@@ -926,12 +926,12 @@ abstract class HttpClient {
    *
    * The following environment variables are taken into account:
    *
-   *  * http_proxy
-   *  * https_proxy
-   *  * no_proxy
-   *  * HTTP_PROXY
-   *  * HTTPS_PROXY
-   *  * NO_PROXY
+   *     http_proxy
+   *     https_proxy
+   *     no_proxy
+   *     HTTP_PROXY
+   *     HTTPS_PROXY
+   *     NO_PROXY
    *
    * [:http_proxy:] and [:HTTP_PROXY:] specify the proxy server to use for
    * http:// urls. Use the format [:hostname:port:]. If no port is used a
@@ -963,6 +963,12 @@ abstract class HttpClient {
    *       return HttpClient.findProxyFromEnvironment(
    *           url, {"http_proxy": ..., "no_proxy": ...});
    *     }
+   *
+   * If a proxy requires authentication it is possible to configure
+   * the username and password as well. Use the format
+   * [:username:password@hostname:port:] to include the username and
+   * password. Alternatively the API [addProxyCredentials] can be used
+   * to set credentials for proxies which require authentication.
    */
   static String findProxyFromEnvironment(Uri url,
                                          {Map<String, String> environment}) {
@@ -970,6 +976,34 @@ abstract class HttpClient {
   }
 
   /**
+   * Sets the function to be called when a proxy is requesting
+   * authentication. The proxy used and and the security realm from

[Anders Johnsen, 2013/04/15 07:07:19]

double 'and'. Rewrite first part of the sentence.

[Søren Gjesse, 2013/04/15 07:42:00]

Done.

+   * the server are passed in the arguments [host], [port] and
+   * [realm].
+   *
+   * The function returns a [Future] which should complete when the
+   * authentication has been resolved. If credentials cannot be
+   * provided the [Future] should complete with [false]. If
+   * credentials are available the function should add these using
+   * [addProxyCredentials] before completing the [Future] with the value
+   * [true].
+   *
+   * If the [Future] completes with [true] the request will be retried
+   * using the updated credentials. Otherwise response processing will
+   * continue normally.
+   */
+  set authenticateProxy(
+      Future<bool> f(String host, int port, String scheme, String realm));
+
+  /**
+   * Add credentials to be used for authorizing HTTP proxies.
+   */
+  void addProxyCredentials(String host,
+                           int port,
+                           String realm,
+                           HttpClientCredentials credentials);
+
+  /**
    * Shutdown the HTTP client. If [force] is [:false:] (the default)
    * the [:HttpClient:] will be kept alive until all active
    * connections are done. If [force] is [:true:] any active