Add support for specifying the `Proxy-Authorization` header for the PluginManager

src/main/distrib/data/defaults.properties

diff --git a/src/main/distrib/data/defaults.properties b/src/main/distrib/data/defaults.properties
index 093dd85..6fddf0b 100644
--- a/src/main/distrib/data/defaults.properties
+++ b/src/main/distrib/data/defaults.properties
@@ -582,6 +582,11 @@
 # SINCE 1.7.0
 plugins.httpProxyPort = 
 
+# The HTTP proxy authorization header for plugin manager.
+#
+# SINCE 1.7.0
+plugins.httpProxyAuthorization = 
+
 # Number of threads used to handle miscellaneous tasks in the background.
 #
 # SINCE 1.6.0

src/main/java/com/gitblit/manager/PluginManager.java

diff --git a/src/main/java/com/gitblit/manager/PluginManager.java b/src/main/java/com/gitblit/manager/PluginManager.java
index a43cbdc..bc3be52 100644
--- a/src/main/java/com/gitblit/manager/PluginManager.java
+++ b/src/main/java/com/gitblit/manager/PluginManager.java
@@ -589,7 +589,7 @@
 	protected Proxy getProxy(URL url) {
 		String proxyHost = runtimeManager.getSettings().getString(Keys.plugins.httpProxyHost, "");
 		String proxyPort = runtimeManager.getSettings().getString(Keys.plugins.httpProxyPort, "");
-		
+
 		if (!StringUtils.isEmpty(proxyHost)  && !StringUtils.isEmpty(proxyPort)) {
 			return new Proxy(Proxy.Type.HTTP, new InetSocketAddress(proxyHost, Integer.parseInt(proxyPort)));
 		} else {
@@ -598,7 +598,8 @@
 	}
 
 	protected String getProxyAuthorization(URL url) {
-		return "";
+		String proxyAuth = runtimeManager.getSettings().getString(Keys.plugins.httpProxyAuthorization, "");
+		return proxyAuth;
 	}
 
 	/**