Allow UpdateSite to create the URLConnection

Different UpdateSites may need to connect to URLs differently, this adds a method to UpdateSite which creates the URLConnection that will be used for connecting. This allows an implementation of a password protected UpdateSite which can add the authorization information to the connection prior to returning it.

core/src/main/java/hudson/model/UpdateCenter.java

@@ -1273,6 +1273,9 @@ static URL toUpdateCenterCheckUrl(String updateCenterUrl) throws MalformedURLExc
          * @throws IOException if the validation fails
          */
         public void preValidate(DownloadJob job, URL src) throws IOException {
+            if(job.site != null) {
+                job.site.preValidate(src);
+            }
         }
 
         /**
@@ -1410,6 +1413,10 @@ private static String getSourceUrl(@NonNull URL src, @CheckForNull URLConnection
          * how the connection gets established.
          */
         protected URLConnection connect(DownloadJob job, URL src) throws IOException {
+            if(job.site != null) {
+                return job.site.connect(src);
+            }
+            // fall back to just using the normal ProxyConfiguration if the site is null
             return ProxyConfiguration.open(src);
         }
 

core/src/main/java/hudson/model/UpdateSite.java

@@ -37,6 +37,7 @@
 import hudson.ExtensionList;
 import hudson.PluginManager;
 import hudson.PluginWrapper;
+import hudson.ProxyConfiguration;
 import hudson.Util;
 import hudson.lifecycle.Lifecycle;
 import hudson.model.UpdateCenter.UpdateCenterJob;
@@ -48,6 +49,7 @@
 import java.io.IOException;
 import java.net.URI;
 import java.net.URL;
+import java.net.URLConnection;
 import java.net.URLEncoder;
 import java.nio.charset.StandardCharsets;
 import java.time.Instant;
@@ -202,6 +204,27 @@ public long getDataTimestamp() {
         }
     }
 
+    /**
+     * Opens a connection to the given URL
+     * @param src the url to connect to
+     * @return A {@code URLConnection} for the given src URL
+     * @since TODO
+     */
+    public URLConnection connect(URL src) throws IOException {
+        return ProxyConfiguration.open(src);
+    }
+
+    /**
+     * Validate the URL of the resource before downloading it.
+     *
+     * @param src The location of the resource on the network
+     * @throws IOException if the validation fails
+     * @since TODO
+     */
+    public void preValidate(URL src) throws IOException {
+        // no validation needed in the default setup
+    }
+
     /**
      * Forces an update of the data file from the configured URL, irrespective of the last time the data was retrieved.
      * @return A {@code FormValidation} indicating the if the update metadata was successfully downloaded from the configured update site