1) Create a new user in your Silverbucket environment. You can name the user anything, for example "API User Read-Only" to make the user's purpose clear. 

2) Add the user in your environment's Authorization Group called Full Access Read-Only. Authorization groups can be found in the admin panel.

3) Head over to your environment's Token Management section in System Settings in the admin panel. By clicking Create token you can create an access token for the user you created earlier.

4) Optional: you can set the API user as Stealth, to avoid it confusing other users or listings in Silverbucket