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Note: Because the WS-IssuedToken support builds on the WS-SecurityPolicy support, this is currently only available to "wsdl first" projects.

WS-Trust extends the WS-Security specification to allow issuing, renewing, and validation of security tokens. A lot of what WS-Trust does centers around the use of a "Security Token Service", or STS. The STS is contacted to obtain security tokens that are used to create messages to talk to the services. The primary use of the STS is to acquire SAML tokens used to talk to the service. Why is this interesting?

When using "straight" WS-Security, the client and server need to have keys exchanged in advance. If the client and server are both in the same security domain, that isn't usually a problem, but for larger, complex applications spanning multiple domains, that can be a burden. Also, if multiple services require the same security credentials, updating all the services when those credentials change can by a major operation.

WS-Trust solves this by using security tokens that are obtained from a trusted Security Token Service. A client authenticates itself with the STS based on policies and requirements defined by the STS. The STS then provides a security token (example: a SAML token) that the client then uses to talk to the target service. The service can validate that token to make sure it really came from the trusted STS.