Frappe version 10 api authentication


We need to add an authenticated API to a Frappe v10 Installation. This instance cannot be upgrade currently. So what is the correct way to implement authentication? I see that in user doctype there is a field named Frappe User ID under Third Party Authentication but am unable to find any relevant documentation. Can someone help with this?

Note that API Key & Secret are not available in version 10 of frappe.