  The advance of web services technologies promises to have far-reaching
effects on the Internet and enterprise networks allowing for greater
accessibility of data. The security challenges presented by the web services
approach are formidable. In particular, access control solutions should be
revised to address new challenges, such as the need of using certificates for
the identification of users and their attributes, human intervention in the
creation or selection of the certificates, and (chains of) certificates for
trust management. With all these features, it is not surprising that analyzing
policies to guarantee that a sensitive resource can be accessed only by
authorized users becomes very difficult. In this paper, we present an automated
technique to analyze scenario-based specifications of access control policies
in open and distributed systems. We illustrate our ideas on a case study
arising in the e-government area.
