Where can I find my developer key / Supernova access token ?

You can create your own authentication tokens in the Authentication tab under the Account section of your settings:

1. Click the New authentication token button, located at the top right corner of the Authentication page.

2. In the ”Create authentication” token dialog, enter a name for your token.

3. Click Generate token.

4. The ”Copy generated authentication token” dialog will open. Click Copy to clipboard to copy your token. This is important as you won't be able to see the token again once this dialog is closed.

5. Click Done to close the dialog.

Learn more here.