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The token can then be used on the Resource Server to access the protected resourse.resource.
Please give a real life scenario example...
You wish log on to ChatGPT and you are give the option of either signing in with an account you have already created; sign up for a new account; or continue with Googlel, Microsoft or Apple accounts.
You decide that you want to Continue with Google. You then click 'Continue with Google'. You will be redirected to Google's sign in page.
You sign in with Google after which you have access to your ChatGPT profile.
Therefore in this scenario ChatGPT is the client application. The Authorisation Server Google.