A. Set up an FTP server that both companies can access and export the required financial data to a folder.
B. Set up a VPN between Company A and Company B, granting access only to the ERPs within the connection.
C. Set up a PKI between Company A and Company B and intermediate shared certificates between the two entities.
D. Create static NATs on each entity's firewalls that map to the ERR systems and use native ERP authentication to allow access.