title: How do I interact with Coinbase's API? Why does it always fail?
body: <p>Accessing the Coinbase API used to be really simple: all you needed was an API key. Now you need something called a "nonce" and a "signature". I pass my new API "Secret", the nonce, and the Key in my request, but it returns an "invalid_key" error. What gives?</p>
  
  <p><strong>EDIT March 12th:</strong> <a href="https://stackoverflow.com/a/22362178/2053389">Added a tutorial on interacting with the API via OAuth.</a></p>