1. A method for accessing data, the method comprising: receiving a workflow model described in a workflow language and configured to declare security requirements of a composite application integrating protected data from two or more external network resources, the composite application executing on at least one host server computer according to the workflow model; and executing an authentication service on at least one secure server computer, the authentication service configured to conduct user authentication and authorization to access the protected data at the external network resources on behalf of the composite application.