Advertise our relying party XRDS document

Some OpenID providers, e.g. Yahoo!'s, want this document to
validate the information coming as part of the OpenID login
request we send them.  Its apparently part of the OpenID 2.0
specification, but I wasn't aware of it until today.

Change-Id: I94b72a4825271b37023a73d59a7aed1f5ab18341
Signed-off-by: Shawn O. Pearce <sop@google.com>

gerrit-httpd/src/main/java/com/google/gerrit/httpd/auth/openid/OpenIdModule.java

@@ -42,6 +42,8 @@ public class OpenIdModule extends ServletModule {
     });
 
     serve("/" + OpenIdServiceImpl.RETURN_URL).with(OpenIdLoginServlet.class);
+    serve("/" + XrdsServlet.LOCATION).with(XrdsServlet.class);
+    filter("/").through(XrdsFilter.class);
 
     install(new RpcServletModule(RpcServletModule.PREFIX) {
       @Override

gerrit-httpd/src/main/java/com/google/gerrit/httpd/auth/openid/XrdsFilter.java

@@ -0,0 +1,42 @@
+package com.google.gerrit.httpd.auth.openid;
+
+import com.google.gerrit.server.config.CanonicalWebUrl;
+import com.google.inject.Inject;
+import com.google.inject.Provider;
+import com.google.inject.Singleton;
+
+import java.io.IOException;
+
+import javax.servlet.Filter;
+import javax.servlet.FilterChain;
+import javax.servlet.FilterConfig;
+import javax.servlet.ServletException;
+import javax.servlet.ServletRequest;
+import javax.servlet.ServletResponse;
+import javax.servlet.http.HttpServletResponse;
+
+@Singleton
+class XrdsFilter implements Filter {
+  private final Provider<String> url;
+
+  @Inject
+  XrdsFilter(@CanonicalWebUrl final Provider<String> url) {
+    this.url = url;
+  }
+
+  @Override
+  public void doFilter(ServletRequest request, ServletResponse response,
+      FilterChain chain) throws IOException, ServletException {
+    HttpServletResponse rsp = (HttpServletResponse) response;
+    rsp.setHeader("X-XRDS-Location", url.get() + XrdsServlet.LOCATION);
+    chain.doFilter(request, response);
+  }
+
+  @Override
+  public void init(FilterConfig config) {
+  }
+
+  @Override
+  public void destroy() {
+  }
+}

gerrit-httpd/src/main/java/com/google/gerrit/httpd/auth/openid/XrdsServlet.java

@@ -0,0 +1,71 @@
+// Copyright (C) 2010 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.httpd.auth.openid;
+
+import com.google.gerrit.server.config.CanonicalWebUrl;
+import com.google.inject.Inject;
+import com.google.inject.Provider;
+import com.google.inject.Singleton;
+
+import java.io.IOException;
+
+import javax.servlet.ServletOutputStream;
+import javax.servlet.http.HttpServlet;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+
+@Singleton
+class XrdsServlet extends HttpServlet {
+  private static final String ENC = "UTF-8";
+  static final String LOCATION = "OpenID.XRDS";
+
+  private final Provider<String> url;
+
+  @Inject
+  XrdsServlet(@CanonicalWebUrl final Provider<String> url) {
+    this.url = url;
+  }
+
+  @Override
+  protected void doGet(HttpServletRequest req, HttpServletResponse rsp)
+      throws IOException {
+    final StringBuilder r = new StringBuilder();
+    r.append("<?xml version=\"1.0\" encoding=\"" + ENC + "\"?>");
+    r.append("<xrds:XRDS");
+    r.append(" xmlns:xrds=\"xri://$xrds\"");
+    r.append(" xmlns:openid=\"http://openid.net/xmlns/1.0\"");
+    r.append(" xmlns=\"xri://$xrd*($v*2.0)\">");
+    r.append("<XRD>");
+    r.append("<Service priority=\"1\">");
+    r.append("<Type>http://specs.openid.net/auth/2.0/return_to</Type>");
+    r.append("<URI>" + url.get() + OpenIdServiceImpl.RETURN_URL + "</URI>");
+    r.append("</Service>");
+    r.append("</XRD>");
+    r.append("</xrds:XRDS>");
+    r.append("\n");
+
+    final byte[] raw = r.toString().getBytes(ENC);
+    rsp.setContentLength(raw.length);
+    rsp.setContentType("application/xrds+xml");
+    rsp.setCharacterEncoding(ENC);
+
+    final ServletOutputStream out = rsp.getOutputStream();
+    try {
+      out.write(raw);
+    } finally {
+      out.close();
+    }
+  }
+}