Unable to download Codechef API

Hey guys! I am unable to download the code chef api from the link given( https://api.codechef.com).When I try to access the link I get the following error message “{“status”:“error”,“result”:{“errors”:{“message”:“Not Allowed”}}}”.What to do.Thanks in advance!

Please read this documentation https://developers.codechef.com/#steps-to-implement-oauth2-in-your-application