Code review changes

README.md

 A client library for authenticating with a remote service via OAuth2 on
 behalf of a user, and making authorized HTTP requests with the user's OAuth2
 credentials.
 
 OAuth2 allows a client (the program using this library) to access and
 manipulate a resource that's owned by a resource owner (the end user) and
 lives on a remote server. The client directs the resource owner to an
 authorization server (usually but not always the same as the server that
 hosts the resource), where the resource owner tells the authorization server
 to give the client an access token. This token serves as proof that the
@@ skipping 46 matching lines @@
 /// Either load an OAuth2 client from saved credentials or authenticate a new
 /// one.
 Future<oauth2.Client> getClient() async {
   var exists = await credentialsFile.exists();
 
   // If the OAuth2 credentials have already been saved from a previous run, we
   // just want to reload them.
   if (exists) {
     var credentials = new oauth2.Credentials.fromJson(
         await credentialsFile.readAsString());
-    return new oauth2.Client(identifier, secret, credentials);
+    return new oauth2.Client(credentials,
+        identifier: identifier, secret: secret);
   }
 
   // If we don't have OAuth2 credentials yet, we need to get the resource owner
   // to authorize us. We're assuming here that we're a command-line application.
   var grant = new oauth2.AuthorizationCodeGrant(
-      identifier, secret, authorizationEndpoint, tokenEndpoint);
+      identifier, authorizationEndpoint, tokenEndpoint,
+      secret: secret);
 
   // Redirect the resource owner to the authorization URL. This will be a URL on
   // the authorization server (authorizationEndpoint with some additional query
   // parameters). Once the resource owner has authorized, they'll be redirected
   // to `redirectUrl` with an authorization code.
   //
   // `redirect` is an imaginary function that redirects the resource
   // owner's browser.
   await redirect(grant.getAuthorizationUrl(redirectUrl));
   
@@ skipping 14 matching lines @@
 
   // Once we're done with the client, save the credentials file. This ensures
   // that if the credentials were automatically refreshed while using the
   // client, the new credentials are available for the next run of the
   // program.
   await credentialsFile.writeAsString(client.credentials.toJson());
 
   print(result);
 }
 ```