1. A computer-implemented method of establishing single sign-on capabilities in a multi-tenant database system, the multi-tenant database system supporting a plurality of users and a plurality of tenants, the method comprising: maintaining a common systemwide digital certificate at the multi-tenant database system, wherein the common systemwide digital certificate is configured for use with all of the plurality of users and for all of the plurality of tenants supported by the multi-tenant database system to create single sign-on links between different tenants of the plurality of tenants; receiving, by the multi-tenant database system, a first instruction to create, for a first user of the multi-tenant database system, a first 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 first instruction identifying credential information for authenticating the first user to the second organization; in response to receiving the first instruction, using the common systemwide digital certificate to cause the multi-tenant database system to create the first single sign-on link for the first user; receiving, by the multi-tenant database system, a second instruction to create, for a second user of the multi-tenant database system, a second single sign-on link between a third organization of the multi-tenant database system and a fourth organization of the multi-tenant database system, the second instruction identifying credential information for authenticating the second user to the fourth organization; and in response to receiving the second instruction, using the common systemwide digital certificate to cause the multi-tenant database system to create the second single sign-on link for the second user; wherein the first and second single sign-on links are created without processing a user-assigned digital certificate.