Add OpenID SSO support.

Configuring OPENID_SSO in gerrit.config will allow the admin
to specify an SSO entry point URL so that users clicking on
"Sign In" are sent directly to that URL.

Change-Id: I361b7b74a6f34a199578620540be31d1df0c5fef

gerrit-common/src/main/java/com/google/gerrit/common/data/GerritConfig.java

@@ -28,6 +28,7 @@ import java.util.Set;
 public class GerritConfig implements Cloneable {
   protected String registerUrl;
   protected String httpPasswordUrl;
+  protected String openIdSsoUrl;
   protected List<OpenIdProviderPattern> allowedOpenIDs;
 
   protected GitwebConfig gitweb;
@@ -72,6 +73,14 @@ public class GerritConfig implements Cloneable {
     httpPasswordUrl = url;
   }
 
+  public String getOpenIdSsoUrl() {
+      return openIdSsoUrl;
+  }
+
+  public void setOpenIdSsoUrl(final String u) {
+    openIdSsoUrl = u;
+  }
+
   public List<OpenIdProviderPattern> getAllowedOpenIDs() {
     return allowedOpenIDs;
   }