Cross Domain Single Sign On (CDSSO) is a proprietary mechanism from Sun OpenSSO Enterprise, designed before any federation specifications existed. The basic difference between the proprietary CDSSO (as described in Part II, Access Control Using OpenSSO Enterprise) and SAML v2 is that CDSSO uses a single authentication authority, a mechanism to move a cookie between multiple DNS domains. SAML v2, on the other hand, gives you the option of using multiple authentication authorities, with one authority asserting the identity of the user to the other.
CDSSO, in certain cases, is easier to set up and manage than federation but, federation solves a broader set of single sign-on issues than CDSSO. CDSSO requires all policy agents to be configured to use a single OpenSSO Enterprise server. This means only one user identity can exist in the entire system whereas, when using SAML v2, user identities can exist on multiple systems (service providers or identity providers). Because of the single identity in CDSSO interactions, issues such as account mapping, attribute flow and session synchronization are not relevant thus, if you need to implement these features, use SAML v2. If the following points are valid to your planned deployment, CDSSO may be a simpler and more suitable solution than federation.
Only Sun OpenSSO Enterprise and Sun policy agents are involved.
Sun policy agents are configured to use the same OpenSSO Enterprise infrastructure where multiple instances can exist.
OpenSSO Enterprise uses a single user identity store.
Multiple instances of OpenSSO Enterprise (configured for high-availability) must reside in a single DNS domain. Only policy agents can reside in different DNS domains.
For more information on CDSSO, see Chapter 6, Models of the User Session and Single Sign-On Processes.