An API Access Token: Generate a token in Settings >Security and apps> Integration tokens. Use the integration token this generates as your Access Token.
To generate a Client ID and Client Secret, you’ll need access to the Developers menu. From there, create a new application to generate the Client ID and Secret.Use these settings for your new application:
Select OAuth 2 as the Authorization Protocol
Copy the OAuth Callback URL and use this as the Callback URL in Medium.