1. A method for authenticating a principal, comprising: receiving an access request from a first principal for access to a second principal; evaluating a contract to acquire a credential for the first principal; and transmitting the credential to the first principal for use in interacting with the second principal, wherein the credential includes authentication information, aggregated attributes and aggregated policies for use by the first principal in interacting with the second principal, and wherein the contract identifies identifier information for the first principal and an authentication technique for the first principal to authenticate to the second principal, and wherein the contract includes directives that permit attribute information and policies of the first principal to be assembled from a variety of data stores.