I have a need to provide a way for people to select which uploaded/related files fulfill a specific purpose (essentially, which file s provide proof of authorization).  I was hoping to use the TagCsv field and when they select the file, update the tags to indicate which file(s) provide that authorization.

However, it appears that the TagCsv field is not available for files shared to an object record -- only files in a public library. It also appears that tagging is not supported in lightning.

Are there any recommended ways to implement something similar or some way to permit access to the TagCsv field on a contentversion uploaded to (shared with) a record?

My thoughts so far have been:
* Use the description field instead and add my tag at the beginning or end of it.
* Create a join object that implements tagging (RecordId, DocumentId, Tags (long text area)
* Embed a list of Ids in a custom field on the record of all the files selected for this purpose (yuck!)