Multiple Realm Authentication?

Dear All,

On my multiuser application, some resources need to be authenticated (I'm using http digest access authentication.) by user A, as suggestion of RFC 2617, I assign "A@example.com" to these resources. In the same way, the resources need to be authenticated by user B belong to realm "B@example.com". But now I've got trouble, how do I assign the realms to the resources which need to be authenticated by either A or B? (The resources shared by A and B.) Thanks.

Best regards,
Zhi-Qiang Lei
zhiqiang.lei@gmail.com