The use case I'm looking at is:

1. Attach files to records in a custom entity that we've built (this can be manually done by agents)
2. In a service offering, the request form includes an entity_link user option to look up records from this custom entity (we've already granted read permission to all portal users)
3. When the user filling out the form picks a record from the entity_link user option, display clickable links to any attachments the entity record has, so the user can click on them and download the file

I have not seen a way to accomplish this, and from the reading I've done, it could be also that attachments of custom entities are not intended to be accessible from the service portal or outside of the agent interface.

My alternate solution that I am contemplating is to use another repository for the files, such as Sharepoint, and have fields in the custom entity records where the maintainers of the entity data can enter the links to the files in sharepoint. The request form can then display those field values that have the links in the request form by using business rules in the offering that load those values into user options when the user selects a record from the entity_link.

I'm looking for suggestions/advice about this kind of use case and what might be a recommended approach.o