Maybe SCN Support would be better suited for this question. Anyway, I don't think SCN allows users to create signed certificates, only SMP does. They are working on a SSO mechanism for SCN that will make it easier for you to login in the future. See the attached links for details.
http://scn.sap.com/community/about/blog/2013/02/18/tales-of-mystery-and-authentication
http://scn.sap.com/community/about/blog/2013/02/19/a-necessary-update-on-auto-login