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WS-Trust support in CXF builds upon the WS-SecurityPolicy implementation to handle the IssuedToken policy assertions that could be found in the WS-SecurityPolicy fragment.

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.

When the WS-SecurityPolicy runtime in CXF encounters an IssuedToken assertion in the policy, the runtime requries an instance of org.apache.cxf.ws.security.trust.STSClient to talk to the STS to obtain the required token. Since the STSClient is a WS-SecurityPolicy client, it will need configuration items to be able to create it's secure SOAP messages to talk to the STS.

There are several ways to configure the STSClient:

Direct configuration of an STS bean in the properties:
In this scenario, a STSClient object is created directly as a property of the client object. The wsdlLocation, service/endpoint names, etc... are all configured in line for that client. 

<jaxws:client name="{http://cxf.apache.org/}MyService" createdFromAPI="true">
    <jaxws:properties>
        <entry key="ws-security.sts.client">
            <!-- direct STSClient config and creation -->
            <bean class="org.apache.cxf.ws.security.trust.STSClient">
                <constructor-arg ref="cxf"/>
                <property name="wsdlLocation" value="target/wsdl/trust.wsdl"/>
                <property name="serviceName" value="{http://cxf.apache.org/securitytokenservice}SecurityTokenService"/>
                <property name="endpointName" value="{http://cxf.apache.org/securitytokenservice}SecurityTokenEndpoint"/>
                <property name="properties">
                    <map>
                       <entry key="ws-security.username" value="alice"/>
                       <entry key="ws-security.callback-handler" value="client.MyCallbackHandler"/>
                       <entry key="ws-security.signature.properties" value="clientKeystore.properties"/>
                       <entry key="ws-security.encryption.properties" value="clientKeystore.properties"/>
                       <entry key="ws-security.encryption.username" value="mystskey"/> 
                    </map>
                </property>
            </bean>            
        </entry> 
    </jaxws:properties>
</jaxws:client>

The above example shows a configuration where the STS uses the UsernameToken profile to validate the client. It is assumed the keystore identified within clientKeystore.properties contains both the private key of the client and the public key (identified above as mystskey) of the STS; if not, create separate property files for the signature properties and the encryption properties, pointing to the keystore and truststore respectively.

Remember the jaxws:client createdFromAPI attribute needs to be set to true (as shown above) if you created the client programmatically via the CXF API's--i.e., Endpoint.publish() or Service.getPort().

This also works for "code first" cases as you can do:

STSClient sts = new STSClient(...);
sts.setXXXX(....)
.....
((BindingProvider)port).getRequestContext().put("ws-security.sts.client", sts);

Sample clientKeystore.properties format:

org.apache.ws.security.crypto.provider=org.apache.ws.security.components.crypto.Merlin
org.apache.ws.security.crypto.merlin.keystore.type=jks
org.apache.ws.security.crypto.merlin.keystore.password=KeystorePasswordHere
org.apache.ws.security.crypto.merlin.keystore.alias=ClientKeyAlias
org.apache.ws.security.crypto.merlin.file=NameOfKeystore.jks

Indirect configuration based on endpoint name:
If the runtime does not find a STSClient bean configured directly on the client, it checks the configuration for a STSClient bean with the name of the endpoint appended with ".sts-client". For example, if the endpoint name for your client is "{http://cxf.apache.org/}TestEndpoint", then it can be configured as:

<bean name="{http://cxf.apache.org/}TestEndpoint.sts-client" 
    class="org.apache.cxf.ws.security.trust.STSClient" abstract="true">
    <property name="wsdlLocation" value="WSDL/wsdl/trust.wsdl"/>
    <property name="serviceName" value="{http://cxf.apache.org/securitytokenservice}SecurityTokenService"/>
    <property name="endpointName" value="{http://cxf.apache.org/securitytokenservice}SecurityTokenEndpoint"/>
    <property name="properties">
        <map>
            <entry key="ws-security.sts.token.properties" value="etc/bob.properties"/>  
            <entry key="ws-security.callback-handler" value="interop.client.KeystorePasswordCallback"/>
            <entry key="ws-security.signature.properties" value="etc/alice.properties"/> 
            <entry key="ws-security.encryption.properties" value="etc/bob.properties"/>	
        </map>
    </property>
</bean>

This properties configured in this example demonstrate STS validation of the client using the X.509 token profile. The abstract="true" setting for the bean defers creation of the STSClient object until it is actually needed. When that occurs, the CXF runtime will instantiate a new STSClient using the values configured for this bean.

Default configuration:
If an STSClient is not found from the above methods, it then tries to find one configured like the indirect, but with the name "default.sts-client". This can be used to configure sts-clients for multiple services.

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