MSO and multiple communities

[Dave Morris]

Guy Rixon wrote:

>OK...in that case S only trusts a group warrant from C2 if the warrant is
>names an indivdual account, at some Ci and S also trusts Ci.  I.e., the group
>warrant can't say 'the bearer of the public key xyz is a member of group G';
>it has to say that 'the caller X is a member of group G provided that you
>can authenticate X as individual user I'.  Possible, but we'd better be aware
>of the distinction.
>  
>
Yep.
To call a service with identity I as a member of group G you would need 
two warrants.
One from your home Community, Ch, to say 'this certifies the bearer is I'
One from the Community, Cg, that manages the members of group G  to say 
'this certifies I is a member of the group G'.

The service needs to trust both Ch and Cg.

This may sound like a lot of work for the service developer and service 
provider.
However, a lot of it can be off loaded to a (local) Community.

If the service S trusts a (local) Community Cs, then when it recieves 
all of the warrants in a message, the service should be able to just 
bung the whole lot at the local Community service Cs and ask it 'is this 
lot valid ?'. The Community service can then work out the details, 
checking the group memberships are signed correctly etc.

It means that if an institute provides multiple services, they only need 
to assign the trust relationships in one place.
All of the local services trust Cs, and the administrator of Cs decides 
if they trust other Communities, Cx and Cy.

Note, (local) is in brackets because it would normally be local to an 
Institute, but it could be a remote Community managed by someone else.

Dave