source: doc/usage_scenario @ 4721618

You (Acme, Inc.) are running a service and you would like to use ABAC to
authenticate users before they can buy rockets from you. Abstractly,
your local set of credentials (as encoded by XML attribute
certificates) looks like this:

    Acme.buy_rockets <- Acme.preferred_customer

When you launch your service, you will create an ABAC context and load
your identity certificate and the attribute certificate that encodes the
above credential.

You have issued the following attribute (encoded in an XML attribute
cert), which is held by a user of your service:

    Acme.preferred_customer <- Coyote

The Coyote will begin an SSL session to your service using his
self-signed X509 identity certificate and will present this XML
attribute certificate in the body of his message. You will clone the
ABAC context and add the Coyote's identity certificate and the attribute
certificate asserting that he is a preferred customer.

You then issue a query asking:

    Acme.buy_rockets <-?- Coyote

The prover will return that this is in fact true and will return the set
of credentials that proves this, namely:

    Acme.buy_rockets <- Acme.preferred_customer
    Acme.preferred_customer <- Coyote

NOTES

The credentials above are abstract representations. In actual
credentials, 'Acme' and 'Coyote' would be represented by the SHA1 of
their public keys.

Given the above scenario, you can feel secure in selling rockets to the
Coyote because he has established an SSL session using his certificate,
indicating that he holds its private key.