add 'Signin' pseudo-service URLs for building auth consent form URLs.

lib/urls.js

@@ -42,6 +42,15 @@ exports.buildRequestUrl = function(options) {
       else url = "https://svcs.ebay.com/MerchandisingService";
       break;
 
+    // this is not a real service, it's more of a meta-service. the name is made up here.
+    // it's also not really an API - it's used for HTML consent pages -
+    // but other URLs for eBay's systems are here, so including this here too.
+    // @see http://developer.ebay.com/devzone/guides/ebayfeatures/Basics/Tokens-MultipleUsers.html
+    case 'Signin':
+      if (options.sandbox) url = 'https://signin.sandbox.ebay.com/ws/eBayISAPI.dll';
+      else url = 'https://signin.ebay.com/ws/eBayISAPI.dll';
+      break;
+
     default:
       if (options.sandbox) {
         throw new Error("Sandbox endpoint for " + serviceName + " service not yet implemented. Please add.");