We search for web service (with API and human interface) that allows us (or our clients) to semi-publicly share documents or information.
documents should not be searchable in the Internet
the service must be trustable - the user who download document should be able to trust the origin (uploading company/client) of the document. The service should list the uploading companies and their ID/contact somewhere. So every downloader should be able to check/trust the validity of document origin.
some documents should be shared non-publicly - password/hash/qrcode should be required to access the file (in some cases two factors - for example password and link)
What are the services/applications matching these requirements?