Step 1: Create an External Client App and Configure Policies
Make sure you have the public key file saved on your system. When you create the ExternalClientApp, you’ll require the file to upload. If you don’t have a self-signed certificate, follow the steps to Create a Private Key and Self-Signed Digital Certificate.
From Setup, in the Quick Find box, enter External Client Apps.
Click External Client App and then click New External Client App.