To get started with the API authentication, login to your account and select the Settings wheel in the lower left corner, then Integrations in the middle of the page.
Scroll towards the bottom of the page until you see OAuth2 Clients. Insert a name such as "<Client Name> API" in the Name field and paste https://localhost in the Redirect URL field. Then, select Generate New Client.
After generating, you'll see the long alphanumeric Client ID and select "show secret" to view the Client Secret.
You can exchange the Client ID and Client Secret to generate an access code valid for 4 hours. If you only want to use the API for personal use, the easiest way to get an access token would be to use the Client Credentials grant type to request an access token for the user associated with the client you are using.
If you have any questions about authenticating the API, please contact firstname.lastname@example.org.