1. A computer-implemented method for providing a first set of user credentials over a public network to a first remote computer application, the method comprising: storing a plurality of sets of user credentials including the first set of user credentials for the first remote computer application in a central repository that is accessible through an interoperability network configured to facilitate messaging and mediate policy differences among a plurality of independent service providers in communication with the interoperability network, each set of user credentials corresponding to one of a plurality of remote computer applications under control of a corresponding one of the independent service providers, the independent service providers being non-federated entities that do not employ a common identity federation protocol, the independent service providers including a first service provider corresponding to the first remote computer application, and a second service provider corresponding to a second remote computer application, wherein at least some of the remote computer applications communicate with the interoperability network via different access points on the public network; storing a plurality of permissions in a storage medium that is accessible through the interoperability network, the plurality of permissions including a first permission for the second service provider to act on behalf of a first user with respect to the first remote computer application, the first user corresponding to multiple ones of the sets of user credentials including the first set of user credentials; transmitting a request to the second remote computer application corresponding to the second service provider to perform, on behalf of the first user, a particular task involving the first remote computer application corresponding to the first service provider; determining, based on one or more of the permissions stored in the storage medium, whether the second service provider has been granted permission to act on behalf of the first user with respect to the first remote computer application; and when the second service provider has permission to act on behalf of the first user, allowing the second remote computer application to retrieve the first set of user credentials for the first remote computer application from the central repository and to supply the retrieved first set of user credentials to the first remote computer application.