In order to take advantage of the Disqus API, you'll first need to register an API application here.
After registering you'll be provided with a Public and Secret API key here.
You'll need these keys if you're looking to pull JSON data through the API or setup Single Sign-On (SSO) authentication. Access to Single Sign-On is currently available as a free add-on for your Disqus account. Please contact our support team via this contact form and ask them to enable it for your account if you're interested.