Register an OAuth application
When you register your application on ArcGIS, you are provided with the authorization credentials (client ID and client secret) necessary for initiating either ArcGIS identity or application credentials.
Follow these steps to register your app and generate your credentials:
If you do not already have an account, sign up for either an ArcGIS Developer subscription or an ArcGIS Online Organizational Trial.
Sign in to ArcGIS Developer.
Click the OAuth 2.0 tab.
Click + New Application and enter your application's details to register your new app.
After registration, you are shown the application overview; locate your Client ID and Client Secret.
You will need your Client ID and Client Secret for OAuth 2.0 ArcGIS identity authorization.