Begin with the Runkeeper Registration/Authorization page for general instructions to get started. This page points to the Application Portal you can use to establish your application. You'll obtain client_id and client_secret by registering a personal application in that portal.
Then obtain code by submitting a request to https://runkeeper.com/apps/authorize with the following parameters directly from the Runkeeper instructions:
client_id: The unique identifier that your application received upon registration
code: coderedirect_uri: The page on your site where the Health Graph API should redirect the user after accepting or denying the access request