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Tech Life of Recht » archive for 'ws-*'

 Using ActAs with Metro

  • January 5th, 2010
  • 12:18 pm

Yesterday, I wrote about how to implement an STS with Metro. The reason for implementing an STS in the first place is that it enables identity delegation, something you probably want if you need to access a service on behalf of a specific user. The general flow is that the user authenticates, probably using SSO of some kind, and access a website. The site invokes a service on behalf of the user, and the service needs to be pretty sure that the user is actually sitting in the other end, even though there is no direct communication between the user and the service. The job of the STS is to be the one, everybody trusts, so that when the STS issues a token which says that the user is valid, then the service can trust that this is actually the case.

All of this can be done more or less automatically with Metro (at least when using a nightly build) by using this service policy:
[code]





urn:localsts

http://docs.oasis-open.org/wss/oasis-wss-saml-token-profile-1.1#SAMLV2.0
http://docs.oasis-open.org/ws-sx/ws-trust/200512/PublicKey






















[/code]

Here, we express that the service requires an issued token of type SAML 2.0. Issued token means that the token has been created by an STS. In this case, we specify that the STS identified by urn:localsts must issue a token of type SAML 2.0. The exact location of the STS needs to be configured in the client.

Unfortunately, WS-SecurityPolicy does not make it possible to express the requirements for the WS-Trust Issue request. When using identity delegation, two sets of credentials should be passed to the STS: The client credentials, for example an X509Token or a UsernameToken, and the user credentials. The client credentials are provided using standard WS-Security mechanisms, and the user credentials are included in the Issue request using the ActAs element.

As shown in the STS example, the STS policy file takes care of the client credentials by specifying the appropriate tokens. The user credentials token cannot, however, be expressed in the policy, so it needs to be agreed upon out of band. This also means that you have to provide it manually to the client.

Luckily, it’s pretty easy to add an ActAs token to the client. Normally, the client is generated using wsimport. In this example, the service is called ProviderService:
[code]
DefaultSTSIssuedTokenConfiguration config = new DefaultSTSIssuedTokenConfiguration();
config.setSTSInfo(“http://docs.oasis-open.org/ws-sx/ws-trust/200512”,
“http://localhost:8080/sts/sts”,
“http://localhost:8080/sts/sts?wsdl”,
“SecurityTokenService”,
“ISecurityTokenService_Port”,
“http://tempuri.org/”);
config.getOtherOptions().put(STSIssuedTokenConfiguration.ACT_AS, createToken());

STSIssuedTokenFeature feature = new STSIssuedTokenFeature(config);
ProviderService service = new ProviderService();
Provider port = service.getProviderPort(feature);
EchoResponse result = port.echo(new Echo());
[/code]

Here, we create a new configuration object, set the endpoint information for the STS, and add an ActAs token. The contents of the ACT_AS attribute should be an instance of com.sun.xml.ws.security.Token, for example a com.sun.xml.wss.saml.Assertion. Normally, you don’t generate the token yourself. Instead, you get it as part of the initial authentication response – for example, if you’re using SAML 2.0 web SSO, one of the attributes received might be the ActAs token that should be passed to the STS when invoking services.

 Building an STS with Metro

  • January 4th, 2010
  • 10:25 pm

One of my recent tasks has been to see if it was possible to implement an OIO-Trust-compliant STS using the Metro stack from Sun. Metro contains WSIT, which has a number of classes for building an STS, so it’s not that hard. However, large portions of the code is quite undocumented, so I decided to write some of my findings down, hence this post (which is probably only interesing to a very few people).

First of all, OIO-Trust is a Danish WS-Trust profile, which basically says how Issue requests should look. The basic premise is that in order to invoke a SOAP service, you need a token. The STS issues the token based on some criteria using the WS-Trust protocol on top of SOAP.
In OIO-Trust, the Issue request must be signed, and it must contain a so-called bootstrap token. The bootstrap token is a SAML 2.0 assertion. Furthermore, the request must contain the X509 certificate which is used to sign the message. The token requested in the Issue request is a PublicKey (that is, asymmetric) of type SAML 2.0. So, the input is a SAML 2.0 assertion, and the output is also a SAML 2.0 token. More specifically, the output is a holder-of-key token, which has the requestors X509 certificate in the SubjectConfirmationData. The assertion is signed by the STS, and contains by default all the attributes from the input assertion.

In order to create an STS using Metro, you need to

  • Configure the Metro servlet in web.xml
  • Implement a simple STS endpoint class
  • Create a WSDL and a security policy
  • Create a number of services for handling attributes, configuration, etc

Configuring web.xml
This assumes that you’re using a simple servlet container. If the container supports JAX-WS, it shouldn’t be necessary.
When using Metro, all requests go through the same servlet, the WSServlet. The exact endpoint implementation used is then configured in another file, WEB-INF/sun-jaxws.xml. Therefore, simply add the following to web.xml:
[code] com.sun.xml.ws.transport.http.servlet.WSServletContextListener
sts
com.sun.xml.ws.transport.http.servlet.WSServlet
1


sts
/services/*

[/code]

This maps all requests to /services to Metro.

Implement the STS endpoint
Implementing the endpoint is quite simple, as it’s simply a question of extending a Metro class and injecting a resource. Here is a basic implementation:
[code]
import javax.annotation.Resource;
import javax.xml.transform.Source;
import javax.xml.ws.Provider;
import javax.xml.ws.Service;
import javax.xml.ws.ServiceMode;
import javax.xml.ws.WebServiceContext;
import javax.xml.ws.WebServiceProvider;
import javax.xml.ws.handler.MessageContext;

import com.sun.xml.ws.security.trust.sts.BaseSTSImpl;

@ServiceMode(value=Service.Mode.PAYLOAD)
@WebServiceProvider(wsdlLocation=”WEB-INF/wsdl/sts.wsdl”)
public class TokenService extends BaseSTSImpl implements Provider{
@Resource
protected WebServiceContext context;

protected MessageContext getMessageContext() {
MessageContext msgCtx = context.getMessageContext();
return msgCtx;
}
}

[/code]

No changes should be necessary, as the BaseSTSImpl class will handle all WS-Trust communication. What you need to do is to configure the base class according to the local requirements. More on that a little later.

In order to wire the STS endpoint into Metro, you need to create a WEB-INF/sun-jaxws.xml file. The file should contain something like this:

[code]



[/code]

This binds the TokenService implementation to the url /services/sts using SOAP 1.1 (specified by the binding attribute).

Creating the WSDL and policy file
This is by far the hardest part of creating an STS for Metro. The WSDL should be pretty standard, and the same file can be used for all implementations. However, the WSDL file must also contain a security policy, as defined by WS-SecurityPolicy, and writing the policy can be pretty complicated. Netbeans has some support for writing policies, but I prefer to do it by hand because then you’re sure what you’ll get (once you understand WS-SecurityPolicy, that is).

The WSDL file tends to get somewhat large, so I won’t include it here – instead, you can download it if you want to see it. Basically, the WSDL is split into two parts: The regular WSDL stuff with types, messages, porttypes, bindings, and services, and the WS-SecurityPolicy stuff. Normally, the policy consists of 3 parts: The service policy which defined which tokens should be used, and how the security header layout should be, a policy which defines signature and encryption requirements for the request, and a policy for the response. These parts are then wired into the normal WSDL using PolicyReference elements.
In the example file, the service policy defines that we’re using an asymmetric binding (that is, the tokens should be different in the request and response – for example when using public/private keys). The policy also says something about the layout, and that the security header must contain a timestamp. Finally, it also enabled WS-Addressing.

Because this is an STS, the WSDL also contains a third part, namely static configuration of the STS. This includes configuring which certificates to use, how to validate incoming requests, and how tokens should be created.

Basically, this finishes the configuration of a very basic STS. However, there are some aspects which probably require some adjustments.

Checking if the requesting entity is allowed to access the requested service
When a client requests a new token, it includes a reference to the service in the AppliesTo element. Sometimes, there might be restrictions on who can access what. The Metro STS can check if the client is allowed to access a service by implementing the com.sun.xml.ws.api.security.trust.STSAuthorizationProvider interface. The interface has one method, isAuthorized(subject, appliesTo, tokenType, keyType), which returns true or false:
[code]
package dk.itst.oiosaml.sts;

import javax.security.auth.Subject;
import com.sun.xml.ws.api.security.trust.STSAuthorizationProvider;

public class AutorizationProvider implements STSAuthorizationProvider {

public boolean isAuthorized(Subject subject, String appliesTo, String tokenType, String keyType) {
return true;
}
}
[/code]

Metro uses the standard JDK service mechanism to discover implementations of this interface. That means that you should create the file /META-INF/services/ under your source directory and populate the file with the fully qualified classname of the implementation – in this example, create /META-INF/services/com.sun.xml.ws.api.security.trust.STSAuthorizationProvider with the contents dk.itst.oiosaml.sts.AuthorizationProvider.

Speficying attributes
Normally, you probably want to be able to configure the contents of the generated assertion, at the very least the attributes used, as well as the NameID of the subject. This is also done using a service implementation, this time using the com.sun.xml.ws.api.security.trust.STSAttributeProvider interface.

The STSAttributeProvider interface has one method, getClaimedAttributes(subject, appliesTo, tokenType, claims), which returns a map of all the attributes and their values.

The subject contains information about the requesting client, in our example identified by a X509 certificate. The claims object contains any claims included in the request. It also holds any tokens included in OnBehalfOf or ActAs. These tokens are placed in claims.getSupportingProperties(), where they can be read as Subject objects. Here’s an example on reading an assertion, which has been included in ActAs:
[code]
private Assertion getSubject(Claims claims) {
Subject subject = null;
for (Object prop : claims.getSupportingProperties()) {
if (prop instanceof Subject) {
subject = (Subject) prop;
}
}
if (subject != null) {
Set creds = subject.getPublicCredentials(Element.class);
if (!creds.isEmpty()) {
Element assertion = creds.iterator().next();
try {
Assertion saml = SAMLAssertionFactory.newInstance(SAMLAssertionFactory.SAML2_0).createAssertion(assertion);
return saml;
} catch (Exception e) {
e.printStackTrace();
}
}
}
return null;
}
[/code]

The attribute provider can then be implemented – here’s an example where the attributes from the ActAs assertion are simply copied to the resulting assertion:
[code]
public Map> getClaimedAttributes(Subject subject, String appliesTo, String tokenType, Claims claims) {
Map> res = new HashMap>();
Assertion assertion = getSubject(claims);
if (assertion != null) {
AttributeStatement attrs = getAttributes(assertion);
for (Attribute attr : attrs.getAttributes()) {
List values = new ArrayList();
for (Object val : attr.getAttributes()) {
values.add(val.toString());
}
res.put(new QName(attr.getName()), values);
}
}

res.put(new QName(assertion.getSubject().getNameId().getNameQualifier(),
STSAttributeProvider.NAME_IDENTIFIER),
Collections.singletonList(assertion.getSubject().getNameId().getValue()));
return res;
}
[/code]

Notice the last statement, where the NameID is added. The Metro STS will check if an attribute with the name STSAttributeProvider.NAME_IDENTIFIER is present, and in that case use that as the NameID of the subject in the generated assertion.

Handling configuration
The Metro STS must be know all services for which it can issue tokens. These services can either be configured statically in the WSDL file, or they can be provided programmatically. The static configuration is probably only interesting when developing, in a production environment, you probably want to build a nice admin console where services can be added and removed at runtime.

Static configuration takes place in the STSConfiguration element in the WSDL file. It can contain a ServiceProviders tag, which can then contain a number of ServiceProvider tags. Each ServiceProvider must be configured with an endpoint (the AppliesTo value), a certificate, and a token type:

[code]

36000
com.sun.xml.ws.security.trust.impl.WSTrustContractImpl
urn:localtokenservice


poc-provider
http://docs.oasis-open.org/wss/oasis-wss-saml-token-profile-1.1#SAMLV2.0



[/code]

The static configuration also contains information about the STS’ own id (the Issuer element), as well as the lifetime of issued tokens. The CertAlias value of a ServiceProvider must point to an alias in the trust store.

Programmatic configuration
Controlling configuration programmatically is a question of providing a service implementation of com.sun.xml.ws.api.security.trust.config.STSConfigurationProvider. This interface has a single method, getSTSConfiguration(), which returns a configuration object – either your own implementation or an instanceof DefaultSTSConfiguration.

That more or less concludes my findings for now. There are a number of details I haven’t covered here, but I’ll wait with that until another time.

 REST vs WS-*

  • April 22nd, 2008
  • 8:10 pm

Today, we had the OIOREST workshop, a workshop on the OIOREST initiative, we’re a part of at Trifork. The workshop was meant to inform about REST in the Danish public sector and to hear what users and developers had to say. The workshop went pretty well – not a lot was changed, but at least we were (more or less) confirmed in our view that REST does have its place.
The workshop was centered around a couple of Open Space sessions. One of the topics discussed was “REST vs WS-*”. While working with OIOREST, this topic has come up again and again: What is REST in relation to SOAP and WS-*, and when should each be used? This has been the basis for many heated discussions, and today was not much different. Most people say something like “REST is for simple things, but when things get too complicated, you’ll want to use WS-*”. I can’t really figure out what to think about this. First of all, what is simple and what is complicated? Complicated scenarios often include transactions and reliability. Distributed transactions are evil, period. Reliability is handled in REST by adhering to the HTTP verbs and keeping operations idempotent, so that’s not really a good argument either. Another argument against REST is “now we’ve finally developed all these standards for SOAP, why should we then do the same for REST?”. Ignoring that REST is older than SOAP and WS-*, somehow this argument also feels wrong.

I agree that REST is not for everything: if you want a RPC interface, don’t use REST. If you work in an organization which is committed to SOAP-based web services, don’t use REST (at least not openly). If you have the need for hierarchical data in the message header, REST doesn’t quite fit. If you want to use only GET/PUT/DELETE/POST, it will for example, be hard to implement transfers between two accounts in REST.
Now, everything is possible, and all of this can be modeled in REST, but it’s starting to look wrong and diverge from “real” REST. Something like WS-Security seems hard to implement in a nice way in REST. WS-Security makes it possible to sign and/or encrypt XML payloads transparently. The signature is placed in the SOAP header, and the payload format does not have to support digital signatures directly. If you need end-to-end security, this is a pretty nice thing, and REST does not have something similar. Some payload formats, for example Atom Publishing Protocol, supports signatures as a part of the payload itself. WS-Security still has the advantage that no matter what format you’re using, you can use the same mechanism for signing and checking signatures.

WS-Security has some potential, but I’ve also seen a lot of cases where WS-Security could be replaced by plain SSL instead together with a simple Authorization header. So, the original question is still valid: what are the scenarios where SOAP/WS-* simply cannot be avoided? My guess is that there is no good answer for this, just as there is no good answer to the question “when should we use Ruby instead of Java?”, or “when should we use PostgreSQL instead of MySQL?”. The answers to these questions will depend on who you are, what your experience is, where you’re working, and so on. The only way is probably to try some different scenarios in REST and SOAP and see what approach is most successful – which is what we’re in the process of doing with the Danish Nature and Environment Portal, but more about that another day.