I downloaded an open source project about an IOS app which you can send and receive Email[like Gmail application on phone],the programmer used Google OAuth 2.0. my question is "in order to use Google OAuth 2.0,an app must be registered,how can i register that app?"
Thanks for your answers
I found an answer,in order to use Google API,have to sign in this website[console.developers.google.com],and register your product.After registering,Google gives you valid client ID.