A system and program implement a process for allowing users of third party vendors to access print shop applications without separate authentication. The process includes the steps of creating a query-string having identification information of a third party vendor and authentication information of a user of the third party vendor. The query-string is created in response to the user's access to the third party vendor's web-site, and is contained in an inline frame and encrypted. Upon receiving the encrypted query-string sent from a third party vendor server to a print shop server, the query-string is decrypted. It is then determined whether the user has an existing account on the print shop server. If the user has an existing account, the user is automatically logged into the print shop server so that the user may access and use any print-on-demand applications on the print shop server without manually inputting user authentication information on the print shop server.