1. A computer-implemented method of establishing single sign-on capabilities in a multi-tenant database system, the method comprising: maintaining a cross-tenant and cross-user systemwide digital certificate at the multi-tenant database system; receiving an instruction to create, for a user of the multi-tenant database system, a single sign-on link between a first organization of the multi-tenant database system and a second organization of the multi-tenant database system, the instruction identifying credential information for authenticating the user to the second organization; and in response to receiving the instruction, using the cross-tenant and cross-user systemwide digital certificate to create the single sign-on link for the user.