Q: Do you have a public API?
A: Yes. It is documented here: docs.api.autoretouch.com
Q: Do I need to contact you for getting an access token/API key?
A: No. Your normal autoRetouch account is enough. Just use the documented device authorization flow to get everything you need.
Q: What ClientID do I need for API access?
Yes, it is the public documented one (docs.api.autoretouch.com). Yes it is the same for all API accessing clients (expect some internal autoRetouch ones). No there is no customer specific one. The name is miss leading, but cannot be changed due to OAuth/authorization backend requirements.