Generate token and use any httpclient to consume rest api

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API

Java8

client-server

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Hi there, I am writing service consume where my consume service make the get request to given endpoint, but there is a problem, which I can not understand that how can I solve it? following link you can read documentation which I develop right know.
Montonio Payments Documentation[^]

My problem is as I understand When I prepare api not client there are generate token which any can be log in users used to this token which accept any resource, but as I understand if I prepare service consume than people, who prepare api service tell me that it is our token and send the token if you want to used to this api. Can someone explain this? I writing in java using spring boot. But I have no idea. How to generate token which can be usely service consume.

What I have tried:

I didn't tried to discribe What I understand.