SAP Service Marketplace is served by a cluster of servers and while you are browsing through the portal, you might switch to different server. With each time you will be prompted to authenticate yourself. If you want to type in your S-User ID and password each time, you can configure Single Sign-on using SAP Passport (client-certificate that authenticates you) by following these steps:
- Login to http://service.sap.com/myprofile and click on "Maintain my Single Sign-On Certificate"
- Enter your S-User ID password and click on "Apply for SAP Passport"
- Private certificates will be installed in your browser trust store
- Restart your browser and the next the you call SMP you will be able to authenticate using the client certificate.