Wednesday, June 13, 2018

Combining Keycloak with the Apache CXF STS

The Apache CXF STS (Security Token Service) is a web service (both SOAP and REST are supported) that issues tokens (e.g. SAML, JWT) to authenticated users. It can also validate, renew and cancel tokens. To invoke successfully on the STS, a user must present credentials to the STS for authentication. The STS must be configured in turn to authenticate the user credentials to some backend. Another common requirement is to retrieve claims relating to the authenticated user from some backend to insert into the issued token.

In this post we will look at how the STS could be combined with Keycloak to both authenticate users and to retrieve the roles associated with a given user. Typically, Keycloak is used as an IdM for authentication using the SAML SSO or OpenId Connect protocols. However in this post we will leverage the Admin REST API.

I have created a project on github to deploy the CXF STS and Keycloak via docker here.

1) Configuring the STS

Checkout the project from github. The STS is configured is a web application that is contained in the 'src' folder. The WSDL defines a single endpoint with a security policy that requires the user to authenticate via a WS-Security UsernameToken. The STS is configured in spring. Essentially we define a custom 'validator' to validate the UsernameToken, as well as a custom ClaimsHandler to handle retrieving role claims from Keycloak. We also configure the STS to issue SAML tokens.

UsernameTokens are authenticated via the KeycloakUTValidator in the project source. This class is configured with the Keycloak address and realm and authenticates received tokens as follows:

Here we use the Keycloak REST API to search for the user matching the given username, using the given username and password as credentials. What the client API is actually doing behind the scenes here is to obtain an access token from Keycloak using the OAuth 2.0 resource owner password credentials grant, something that can be replicated with a tool like curl as follows:
  • curl --data "client_id=admin-cli&grant_type=password&username=admin&password=password" http://localhost:9080/auth/realms/master/protocol/openid-connect/token -v
  • curl -H "Authorization: bearer <access token>" http://localhost:9080/auth/admin/realms/master/users -H "Accept: application/json" -v
Keycloak will return a HTTP status code of 401 if authentication fails. We allow the case that Keycloak returns 403 unauthorized, as the user may not be authorized to invoke on the admin-cli client. A better approach would be to emulate Apache Syncope and have a "users/self" endpoint to allow users to retrieve information about themselves, but I could not find an analogous endpoint in Keycloak.

Role claims are retrieved via the KeycloakRoleClaimsHandler. This uses the admin credentials to search for the (already authenticated) user, and obtains the effective "realm-level" roles to add to the claim.

2) Running the testcase in docker

First build the STS war and create a docker image for the STS as follows:
  • mvn clean install
  • docker build -t coheigea/cxf-sts-keycloak . 
This latter command just deploys the war that was built into a Tomcat docker image via this Dockerfile. Then pull the official Keycloak docker image and start both via docker-compose (see here):
  • docker pull jboss/keycloak
  • docker-compose up
This starts the STS on port 8080 and Keycloak on port 9080. Log on to the Keycloak administration console at http://localhost:9080/auth/ using the username "admin" and password "password". Click on "Roles" and add a role for a user (e.g. "employee"). The click on "Users" and add a new user. After saving, click on "Credentials" and specify a password (unselecting "Temporary"). Then click on "Role Mappings" and select the role you created above for the user.

Now we will use SoapUI to invoke on the STS. Download it and create a new SOAP project using the WSDL of the STS (http://localhost:8080/cxf-sts-keycloak/UT?wsdl). Click on 'Issue' and select the request. We need to edit the SOAP Body of the request to instruct the STS to issue a SAML Token with a Role Claim using the standard WS-Trust parameters:

     <t:TokenType xmlns:t=""></t:TokenType>
     <t:KeyType xmlns:t=""></t:KeyType>
     <t:RequestType xmlns:t=""></t:RequestType>
     <t:Claims xmlns:ic="" xmlns:t="" Dialect="">
        <ic:ClaimType xmlns:ic="" Uri=""/>

Click in the Properties box in the lower left-hand corner and specify the username and password for the user you created in Keycloak. Finally, right click on the request and select "Add WSS UsernameToken" and hit "OK" and send the request. If the request was successful you should see the SAML Assertion issued by the STS on the right-hand side. In particular, note that the Assertion contains a number of Attributes corresponding to the roles of that particular user.

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