A system and method are provided for performing file transfers using an HTTP- or HTTPS-based Supplier Transport Gateway to connect Customer and Supplier Repositories located behind their respective firewalls. In some embodiments, the Transport Gateway is placed outside the Supplier firewall, and a Supplier Transport Proxy inside the firewall connects the Transport Gateway to the internal Supplier Repositories. In other embodiments, the Transport Gateway and Transport Proxy are reversed, the Proxy residing outside the Supplier firewall and relaying Customer HTTP/HTTPS traffic to the Transport Gateway inside the firewall, which then connects to the internal Supplier Repositories. In either case, the HTTP- or HTTPS-based Customer Repository connects through a Customer Proxy to the Supplier's Transport Gateway to request file upload/download operations. In turn, the Transport Gateway implements the Supplier's request validation policy, and Supplier Repository routing rules that abstract the Supplier Repository topology to the Customer. The Transport Gateway then performs a corresponding upload/download operation against the selected Supplier Repository using HTTP, HTTPS, FTP, or a similar protocol.