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WS-Trust can be considered as an extension to WS-Security specification which primarily provides methods for managing security tokens and ways to broker the trust relationships. The Web Services trust model explained under the WS-trust specification defines three key participants:

  • Security token service
  • Service Consumer
  • Service provider (Relying party)

Security token service (STS) is a Web Service that issues security tokens based on the requester's needs. The consumer sends token requests to the STS in addition to appending tokens into the actual service request and submitting them to the provider. The service provider makes the authentication decision on the service based on the token provided by STS. The service provider may also request token validations from the STS.

This sample includes step-by-step instructions on how WS-trust concepts can be used with WSO2 SOA middleware.

Scenario

We are going to work on the basic trust establishment scenario in the context of WS-trust specification. A SOAP Web Service consumer requests for a security token from STS. We use WSO2 Identity Server as the token provider. WSO2 Identity Server includes a Security Token Service (STS) which is capable of generating security tokens to build trust relationships.

Once the consumer possesses the necessary security tokens, these tokens are presented in order to authenticate to a Web Service deployed in WSO2 Application Server.

Pre-requisites:

  1. Download and install WSO2 Identity Server
  2. Download and install WSO2 Application Server
  3. Any Java IDE (Eclipse, Idea)
  4. soapUI (optional)

First, we need to figure out how we can start the end-to-end process. Obviously, the consumer initiates the process. But, how does the consumer know that he first needs to talk to a STS in order to consume the Web Service which is deployed in WSO2 application server?

The service provider needs to advertise those requirements through a WS-Policy. So, the starting point of our use case is to configure a policy in the web service.

Then, we need to look into the token provider, WSO2 Identity Server. As I have explained before, WSO2 IS comes with a Security Token Service. We need to configure it to issue tokens to the provider web service and secure STS using a WS-Security policy because the consumers should authenticate themselves to the STS when requesting tokens.

Finally, we will write a client/consumer (or just use a service invocation tool such as soapUI) to request a security token from STS and append it to the actual web service request message to authenticate to the web service which is deployed in WSO2 Application Server.

Step 1 - Secure Web Service with a Claim-aware Security Policy

  1. Start WSO2 Application Server and log in to the management console as a default admin user.
  2. Go to Manage > Services > Add > AAR Service.
  3. Deploy Axis2Service.aar which can be downloaded from here.
  4. Once the service is deployed, we need to associate a security policy for our service. You can find a set of default Web Service security policies in security configuration wizard. However, we cannot use any of them for our scenario.

Our Web Service should be associated with a trust based security policy. A security token which is offered by STS represents a set of claims. A claim defines a specific information about a particular user. For example, first name or email address of the user.

In our example, Axis2Service (the Web Service deployed in service provider, WSO2 Application Server) needs to be made as a claim-aware Web Service. The users who consume the service need to present the claims defined in WS-Security policy.

Thus, we need to secure Axis2Service using a custom policy. You can download the complete policy from here. This is useful if you wish to look into the following element in the custom security policy.

<sp:SupportingTokens xmlns:sp="http://schemas.xmlsoap.org/ws/2005/07/securitypolicy">
                <wsp:Policy>
                    <sp:IssuedToken
                            sp:IncludeToken="http://schemas.xmlsoap.org/ws/2005/07/securitypolicy/IncludeToken/AlwaysToRecipient">
                        <sp:Issuer>
                            <Address xmlns="http://www.w3.org/2005/08/addressing">https://localhost:9444/services/wso2carbon-sts</Address>
                        </sp:Issuer>
                        <sp:RequestSecurityTokenTemplate>
                            <t:TokenType xmlns:t="http://schemas.xmlsoap.org/ws/2005/02/trust">urn:oasis:names:tc:SAML:2.0:assertion</t:TokenType>
                            <t:KeyType xmlns:t="http://schemas.xmlsoap.org/ws/2005/02/trust">http://schemas.xmlsoap.org/ws/2005/02/trust/Bearer</t:KeyType>
                            <t:KeySize xmlns:t="http://schemas.xmlsoap.org/ws/2005/02/trust">256</t:KeySize>
                            <t:Claims Dialect="http://wso2.org/claims"
                                      xmlns:t="http://schemas.xmlsoap.org/ws/2005/02/trust"
                                      xmlns:ic="http://schemas.xmlsoap.org/ws/2005/05/identity">
                                <ic:ClaimType Uri="http://wso2.org/claims/givenname"/>
                                <ic:ClaimType Uri="http://wso2.org/claims/emailaddress"/>
                            </t:Claims>
                        </sp:RequestSecurityTokenTemplate>
                        <wsp:Policy>
                            <sp:RequireInternalReference/>
                        </wsp:Policy>
                    </sp:IssuedToken>
                </wsp:Policy>
</sp:SupportingTokens>

SupportingTokens are used to provide additional claims for a requester (client). Use SupportingToken policy assertion to describe claims which should be given by a consumer to access this particular Web Service.

  • The sp:IssuedToken element defines that the requester must talk to an STS to obtain the token.
  • The sp:IncludeToken attribute value is defined as ../AlwaysToRecipient, which says the token must be included as part of all messages sent from the initiator (service consumer) to the recipient.

  • The Address attribute of sp:Issuer element defines the token issuer whom the consumer must be contacted to get the security token. In other words, the endpoint address of the Security Token Service. In this scenario, it must be the STS URL of IS.

    This is while running WSO2 IS with port-offset 1, hence the https port is 9444.

  • The sp:RequestSecurityTokenTemplate element specifies the structure/type of the token which has to be issued by the STS. Later, you will observe the children of this element will be included as the part of RequestSecurityToken (RST) message which will be sent to the STS by consumer.
  • The t:TokenType element represents the type of the token such as UserNameToken, SAML-1.1, SAML-2.0. In our example, we ask STS To generate SAML-2.0 token by specifying SAML-2.0 token type URL.
  • t:KeyType represents the type of the key desired in security token, can be either public key, symmetric key or bearer. We will ask STS to generate the relatively simple key, bearer token. Bearer token does not require a proof of possession hence it is quite easy to dealt with.
  • t:Claims element defines the claims that must be included in the security token. We will request First Name and email address claims from the consumer.

The First Name claim is mapped to the "http://wso2.org/claims/givenname" URI. We will be able to clear ourselves once we configure the token provider in the next step.

OK, now we understood all elements of the SupportingToken assertion of our custom web service policy. Let's upload the policy to embedded registry in WSO2 Application Service.

  1. Locate /_system/config collection in registry browser and click on Add Resource.
  2. Navigate to the axis2service.policy.xml which you have downloaded from the above location.
  3. Click Add. Now, we have our custom policy in WSO2 Application Server. We can associate the policy to Axis2Service.
  4. Click on the Unsecured link associated with Axis2Service in the Deployed Services page. You are directed to the Security for the service page. 
  5. Navigate to the Policy From Registry section which can be found at the bottom of the page. 
  6. Click on the Configuration Registry icon and select the axis2service.policy.xml from the /_system/config collection.
  7. Click on Next to proceed with the wizard. You are directed to the Activate Security page where you can specify a trusted key store for the Web Service.
  8. Select wso2carbon.jks as the trusted key store. 
  9. As discussed, STS is responsible for issuing tokens. Therefore, the STS is trusted by both consumer as well as the service provider. In order to do so, the public key certificate of STS should be imported to the trusted key store defined here. We do not explicitly do key exchanges in this example because we are using the same wso2carbon.jks keystore in both WSO2 Application Server and WSO2 Identity Server.

Now, we have our Web Service secured with a claim-aware security policy.

Step 2 - STS Configurations

  1. Start WSO2 Identity Server and log in to the management console using the default admin credentials.
  2. Select Secure Token Service from the left menu under the Manage section.
  3. First, we should secure the STS. There are multiple ways to authenticate using the Secure Token Service. The consumer can just present his username and password as UserNameTokens or X509 certificates to the STS. In this example, we will configure the STS using UserNameToken Authentication policy so that the clients should talk to STS by presenting their credentials.
  4. Click on Apply Security Policy in the above screen.
  5. Select UsernameToken from the list of default security policies in the Security for the service page.
  6. Click on Next. Now, we need to select a user group to which the service consumer belongs. We will incorporate our consumer into the admin group and request tokens from STS by presenting the default admin user credentials.
  7. Select admin as the user group and click on Finish.

  8. Next, we need to configure STS to add Axis2Service as a trusted service. In the above screen, enter the HTTP endpoint url of the Axis2Service. 

    Endpoint Address = http://localhost:9765/services/Axis2Service/

  9. Usually, the security token is signed by STS. Thus, it is necessary to select a certificate alias to sign the token. Select the default wso2carbon certificate alias.
  10. Now, check the user profile of admin user who is going to authenticate to the STS. Click on My Profiles at the left menu. The Update Profile form is displayed where you can enter various user attributes such as First Name, Last Name etc.
  11. Make sure to add some values to First Name and Email address fields since we are going to use those as the required claims.
  12. Click on Configure in the left menu and select Claim Management. You find a set of claim dialects associated with the internal user store in IS. Click on the default claim dialect, http://wso2.org/claims. 
  13. Click on First Name claim mapping.
  14. As you can see in the following screen shot, First Name is mapped to givenName attribute.
     

Now, you should be able to understand why we have specified http://wso2.org/claims/givenName as the claimuri for First Name attribute in the service policy.

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