User-Agent and Accept header now required on the API

We’ve made a change to our API that hardens requirements on the headers you send. You now must provide a User-Agent header and an Accept header.

• Your User-Agent header should reflect the name and version of your application, e.g. MtgExampleApp/1.1. Do not allow HTTP libraries to choose the header for you. If you are connecting with browser-based JavaScript, do not change the browser User-Agent.
• The Accept header must be present, but you can provide a generic preference. For example, both of these are okay: Accept: */* and Accept: application/json;q=0.9,*/*;q=0.8.

You can read these requirements in the API documentation.