When you need to develop the integration within only your account, we don’t see a point to complicate the obtaining of Authorization code via the mechanism of redirects. You can get that code when creating an integration in your account. The integration will work with your rights (administrator rights, because an integration can be created only by users that have administrator rights).
First, you will need to do the analogy on what can be found on the Example by steps page, create an integration exactly in the same account, in which you plan to have an integration.
After filling all required fields you will see an Integration ID, Secret key and Authorization code. It means you can skip the steps, connected to the creation of a link for transition and processing of the received parameters, and get to the part of the instructions, that explains the exchange of the authorization code for an access token and refresh token.