You can follow the procedure below to register an app and obtain the OAuth client credentials, the OAuthClientId and OAuthClientSecret. Note that you will need to activate the OAuth plugin for your instance if it is not active already.

1. Log in to your ServiceNow instance.
2. In the Navigator, click System OAuth -> Application Registry.
3. Click New and then click Create an OAuth API Endpoint for External Clients.
4. Select the Active check box, enter a name for the app, and set a Client Secret or leave this blank to have one generated automatically.
5. Enter a value in the Redirect URL box. If you are making a desktop application, set the Redirect URL to http://localhost:33333 or a different port number of your choice. If you are making a web application, set the Redirect URL to a page on your Web app you want the user to be returned to after they have authorized your application.
6. After clicking submit, you may navigate back to the newly created app to take note of the OAuthClientId, OAuthClientSecret, and CallbackURL values.