Hi Jann,
Thank you for reaching out. The Adwords API/Google Ads API use OAuth2 for authentication. Thus you would not be able to use the API key to replace it. When setting up the OAuth consent screen if you choose “Internal” your app will be available to only G Suite users within your organization. If your external users try to use your app, they’ll be blocked with an authorization error screen. If this is what you need then you could choose it as “Internal” otherwise go with the “External” option and the sensitive or restricted user data would be protected by the verification process from Google. Please let me know if you have any further concerns.
Thanks and regards,
Xiaoming, Google Ads API Team