Requests are authorized with a Basic token which requires a client_id and an api_key. The Basic token is the URL-safe Base64 encoding of a string which contains your client_id followed by a : for client side requests and your client_id and your api_key separated by a colon for server side requests. Header format: 
Authorization: Basic {token}

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Client Side Requests

Token format: 
BASE64_ENCODE({client_id}):
Example: 
ABC123 -> QUJDMTIzOg==

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Server Side Requests

Token format: 
BASE64_ENCODE({client_id}:{api_key})
Example: 
ABC123:DEF456 -> QUJDMTIzOkRFRjQ1Ng==