GetUserFilter: Allow to include username in servlet response header

Add a new setting, http.addUserAsResponseHeader, which when enabled
causes the servlet response to include a 'User' header that contains
the name of the logged in user.

This will enable reverse proxies to log the name of the user that
issued the http request.

The new setting is disabled by default.

Change-Id: I5c3c783813f3aa71209320610bb8168a51305cba

Documentation/config-gerrit.txt

@@ -2401,6 +2401,14 @@ Pattern to print user in Tomcat AccessLog.
 +
 Default value is true.
 
+[[http.addUserAsResponseHeader]]http.addUserAsResponseHeader::
++
+If true, the header 'User' will be added to the list of response headers so it
+can be accessed from a reverse proxy for logging purposes.
+
++
+Default value is false.
+
 [[httpd]]
 === Section httpd
 

gerrit-httpd/src/main/java/com/google/gerrit/httpd/GetUserFilter.java

@@ -14,6 +14,7 @@
 
 package com.google.gerrit.httpd;
 
+import com.google.common.collect.ImmutableMap;
 import com.google.gerrit.server.CurrentUser;
 import com.google.gerrit.server.IdentifiedUser;
 import com.google.gerrit.server.config.GerritServerConfig;
@@ -28,33 +29,49 @@ import javax.servlet.FilterConfig;
 import javax.servlet.ServletException;
 import javax.servlet.ServletRequest;
 import javax.servlet.ServletResponse;
+import javax.servlet.http.HttpServletResponse;
 import org.eclipse.jgit.lib.Config;
 
-/** Stores user as a request attribute, so servlets can access it outside of the request scope. */
+/**
+ * Stores user as a request attribute and/or response header, so servlets and reverse proxies can
+ * access it outside of the request/response scope.
+ */
 @Singleton
 public class GetUserFilter implements Filter {
 
-  public static final String REQ_ATTR_KEY = "User";
+  public static final String USER_ATTR_KEY = "User";
 
   public static class Module extends ServletModule {
 
-    private final boolean enabled;
+    private final boolean reqEnabled;
+    private final boolean resEnabled;
 
     @Inject
     Module(@GerritServerConfig Config cfg) {
-      enabled = cfg.getBoolean("http", "addUserAsRequestAttribute", true);
+      reqEnabled = cfg.getBoolean("http", "addUserAsRequestAttribute", true);
+      resEnabled = cfg.getBoolean("http", "addUserAsResponseHeader", false);
     }
 
     @Override
     protected void configureServlets() {
-      if (enabled) {
-        filter("/*").through(GetUserFilter.class);
+      if (resEnabled || reqEnabled) {
+        ImmutableMap.Builder<String, String> initParams = ImmutableMap.builder();
+        if (reqEnabled) {
+          initParams.put("reqEnabled", "");
+        }
+        if (resEnabled) {
+          initParams.put("resEnabled", "");
+        }
+        filter("/*").through(GetUserFilter.class, initParams.build());
       }
     }
   }
 
   private final Provider<CurrentUser> userProvider;
 
+  private boolean reqEnabled;
+  private boolean resEnabled;
+
   @Inject
   GetUserFilter(Provider<CurrentUser> userProvider) {
     this.userProvider = userProvider;
@@ -65,11 +82,19 @@ public class GetUserFilter implements Filter {
       throws IOException, ServletException {
     CurrentUser user = userProvider.get();
     if (user != null && user.isIdentifiedUser()) {
+
       IdentifiedUser who = user.asIdentifiedUser();
+      String loggableName;
       if (who.getUserName() != null && !who.getUserName().isEmpty()) {
-        req.setAttribute(REQ_ATTR_KEY, who.getUserName());
+        loggableName = who.getUserName();
       } else {
-        req.setAttribute(REQ_ATTR_KEY, "a/" + who.getAccountId());
+        loggableName = "a/" + who.getAccountId();
+      }
+      if (reqEnabled) {
+        req.setAttribute(USER_ATTR_KEY, loggableName);
+      }
+      if (resEnabled && resp instanceof HttpServletResponse) {
+        ((HttpServletResponse) resp).addHeader(USER_ATTR_KEY, loggableName);
       }
     }
     chain.doFilter(req, resp);
@@ -79,5 +104,8 @@ public class GetUserFilter implements Filter {
   public void destroy() {}
 
   @Override
-  public void init(FilterConfig arg0) {}
+  public void init(FilterConfig arg0) {
+    reqEnabled = arg0.getInitParameter("reqEnabled") != null ? true : false;
+    resEnabled = arg0.getInitParameter("resEnabled") != null ? true : false;
+  }
 }

gerrit-pgm/src/main/java/com/google/gerrit/pgm/http/jetty/HttpLog.java

@@ -89,7 +89,7 @@ class HttpLog extends AbstractLifeCycle implements RequestLog {
     String uri = req.getRequestURI();
     uri = redactQueryString(uri, req.getQueryString());
 
-    String user = (String) req.getAttribute(GetUserFilter.REQ_ATTR_KEY);
+    String user = (String) req.getAttribute(GetUserFilter.USER_ATTR_KEY);
     if (user != null) {
       event.setProperty(P_USER, user);
     }