GET from rest API with javascript using Authentication headers

I never used Authentication headers with javascript when sending a GET request to a REST API before and i struggle finding anything helpful when searching. This is the API im trying to connect to, but unless you use Authentication headers you simply get the message "Authentication required"

https://developer.bring.com/api/pickup-point/

As listed in the starting guide below i have an account along with an API key, but how do i use these to get a response from the API? https://developer.bring.com/api/#authentication

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