Restrict adding new records to Survey 123 underlying hosted feature layer to only Survey 123 webform or app

[ColForbin]

Currently, because the hosted feature layer associated with a public Survey 123 survey is shared to the public and allows adding new features, a public user could, if they were so inclined, search for and find the feature layer in ArcGIS Online, and add features to that layer through the Map Viewer in AGO, and not using the Survey 123 web form or app.   The downfall of this is that someone could potentially add dozens of meaningless features to the survey's feature layer.

It would be ideal there were a way to restrict the adding of new records to the underlying feature layer of a public Survey 123 survey at the feature layer level based on what application is being used.  Whether this would be a "referrer" setting in the survey to only allow new submissions from survey123.arcgis.com, or perhaps another setting in the Editing settings of the hosted feature layer itself, "only allow new records added using Survey 123 webform or app", or something to that effect.

[jcarlson]

There's no surefire way to prevent this; a public layer is public, for better or worse.

If you want to prevent spamming, however, you could include a hidden field in the form, call it submission_source. The form could auto-fill this field with some secret value that only you know, and submissions without this value could be filtered and removed.

Of course, in order to prevent spammers from seeing this field and intuiting the correct value, you'd need to change the layer's settings to prevent users from seeing records, even those that they add, and only expose the field visibly in a non-public layer.

[ColForbin]

Thanks @jcarlson for the workaround.  Although this would not prevent the features from actually being added, it is a good way to enable filtering and removing these features after the fact.