Improving Web Application Security: Threats and - CGISecurity

Chapter 12: Building Secure Web Services 325Design ConsiderationsBefore you start to develop Web services, there are a number of issues to consider atdesign time. The key security considerations are:● Authentication requirements● Privacy and integrity requirements● Resource access identities● Code access securityAuthentication RequirementsIf your Web service provides sensitive or restrictive information, it needs toauthenticate callers to support authorization. In Windows environments, you can useWindows authentication. However, where you are not in control of both endpoints,WSE provides authentication solutions that conform to the emerging WS-Securitystandard. WSE provides a standard framework for using SOAP headers to passauthentication details in the form of user names and passwords, Kerberos tickets,X.509 certificates, or custom tokens. For more information, see the “Authentication”section later in this chapter.Privacy and Integrity RequirementsIf you pass sensitive application data in Web service requests or response messages,consider how you can ensure that they remain private and unaltered while in transit.WSE provides integrity checking through digital signatures, and it also supportsXML encryption to encrypt sensitive elements of the entire message payload. Theadvantage of this approach is that it is based on the emerging WS-Security standardand that it provides a solution for messages that pass through multiple intermediatenodes.The alternative is to use transport level encryption through SSL or IPSec channels.These solutions are only appropriate where you are in control of both endpoints.Resource Access IdentitiesBy default, ASP.NET Web services do not impersonate, and the least privilegedASPNET process account is used for local and remote resource access. You can usethis ASPNET process account to access remote network resources such as SQLServers that require Windows authentication, by creating a mirrored local account onthe database server.Note On Windows Server 2003, the Network Service account is used by default to run Webservices.