add refreshToken

oauth3.js

@@ -194,6 +194,20 @@
     });
   };
 
+  oauth3.refreshToken = function (providerUri, opts) {
+    return oauth3.discover(providerUri, opts).then(function (directive) {
+      var prequest = core.refreshToken(directive, opts);
+
+      console.log('[DEBUG] [core] refreshToken URL', prequest);
+
+      return oauth3.request({
+        url: prequest.url
+      , method: prequest.method
+      , data: prequest.data
+      });
+    });
+  };
+
   oauth3.frameRequest = function (url, state, opts) {
     var promise;