I'm looking to integrate my Web Form to HubSpot using the API recommended in https://legacydocs.hubspot.com/docs/methods/forms/submit_form It works well But the biggest drawback of this API is that there is NO AUTHENTICATION Anyone who knows or intercepts the API call from the Website will find out the Portal ID & Form Guid and can flood my hubspot instance with lot of Form Submissions.
If this is something you really want, yes. You could look into the ReCaptcha option, but this is something that is not unique. Spam send through forms happen on all type of websites. ReCaptcha is the most common solution. But if I have a WordPress website with an exposed action, that could also be used to send spam through my website.
You could check this post, which has the same question. I do remember to see an update the past month regarding recaptcha and the submission API, not sure if it is relevant tho. Will post it here if I find it.