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7.3. Providing Client Credentials

Overview

There are essentially two approaches to providing UsernameToken client credentials: you can either set both the username and the password directly in the client's Spring XML configuration; or you can set the username in the client's configuration and implement a callback handler to provide passwords programmatically. The latter approach (by programming) has the advantage that passwords are easier to hide from view.

Client credentials properties

Table 7.1, “Client Credentials Properties” shows the properties you can use to specify WS-Security username/password credentials on a client's request context in Spring XML.

Table 7.1. Client Credentials Properties

PropertiesDescription
ws-security.usernameSpecifies the username for UsernameToken policy assertions.
ws-security.passwordSpecifies the password for UsernameToken policy assertions. If not specified, the password is obtained by calling the callback handler.
ws-security.callback-handler
Specifies the class name of the WSS4J callback handler that retrieves passwords for UsernameToken policy assertions. Note that the callback handler can also handle other kinds of security events.

Configuring client credentials in Spring XML

To configure username/password credentials in a client's request context in Spring XML, set the ws-security.username and ws-security.password properties as follows: 
<beans ... >
    <jaxws:client name="{NamespaceName}LocalPortName"
                  createdFromAPI="true">
        <jaxws:properties>
            <entry key="ws-security.username" value="Alice"/>
            <entry key="ws-security.password" value="abcd!1234"/>
        </jaxws:properties>
    </jaxws:client>
    ...
</beans>
If you prefer not to store the password directly in Spring XML (which might potentially be a security hazard), you can provide passwords using a callback handler instead.

Programming a callback handler for passwords

If you want to use a callback handler to provide passwords for the UsernameToken header, you must first modify the client configuration in Spring XML, replacing the ws-security.password setting by a ws-security.callback-handler setting, as follows: 
<beans ... >
    <jaxws:client name="{NamespaceName}LocalPortName"
                  createdFromAPI="true">
        <jaxws:properties>
            <entry key="ws-security.username" value="Alice"/>
            <entry key="ws-security.callback-handler" value="interop.client.UTPasswordCallback"/>
        </jaxws:properties>
    </jaxws:client>
    ...
</beans>
In the preceding example, the callback handler is implemented by the UTPasswordCallback class. You can write a callback handler by implementing the javax.security.auth.callback.CallbackHandler interface, as shown in Example 7.2, “Callback Handler for UsernameToken Passwords”.

Example 7.2. Callback Handler for UsernameToken Passwords

package interop.client;

import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

import javax.security.auth.callback.Callback;
import javax.security.auth.callback.CallbackHandler;
import javax.security.auth.callback.UnsupportedCallbackException;

import org.apache.ws.security.WSPasswordCallback;

public class UTPasswordCallback implements CallbackHandler {
    
    private Map<String, String> passwords = 
        new HashMap<String, String>();
    
    public UTPasswordCallback() {
        passwords.put("Alice", "ecilA");
        passwords.put("Frank", "invalid-password");
        //for MS clients
        passwords.put("abcd", "dcba");
    }

    public void handle(Callback[] callbacks) throws IOException, UnsupportedCallbackException {
        for (int i = 0; i < callbacks.length; i++) {
            WSPasswordCallback pc = (WSPasswordCallback)callbacks[i];

            String pass = passwords.get(pc.getIdentifier());
            if (pass != null) {
                pc.setPassword(pass);
                return;
            }
        }
        
        throw new IOException();
    }
    
    // Add an alias/password pair to the callback mechanism.
    public void setAliasPassword(String alias, String password) {
        passwords.put(alias, password);
    }
}
The callback functionality is implemented by the CallbackHandler.handle() method. In this example, it assumed that the callback objects passed to the handle() method are all of org.apache.ws.security.WSPasswordCallback type (in a more realistic example, you would check the type of the callback objects).
A more realistic implementation of a client callback handler would probably consist of prompting the user to enter their password.

WSPasswordCallback class

When a CallbackHandler is called in a Apache CXF client for the purpose of setting a UsernameToken password, the corresponding WSPasswordCallback object has the USERNAME_TOKEN usage code.
For more details about the WSPasswordCallback class, see org.apache.ws.security.WSPasswordCallback.
The WSPasswordCallback class defines several different usage codes, as follows:
USERNAME_TOKEN
Obtain the password for UsernameToken credentials. This usage code is used both on the client side (to obtain a password to send to the server) and on the server side (to obtain a password in order to compare it with the password received from the client).
On the server side, this code is set in the following cases:
  • Digest password—if the UsernameToken contains a digest password, the callback must return the corresponding password for the given user name (given by WSPasswordCallback.getIdentifier()). Verification of the password (by comparing with the digest password) is done by the WSS4J runtime.
  • Plaintext password—implemented the same way as the digest password case (since Apache CXF 2.4.0).
  • Custom password type—if getHandleCustomPasswordTypes() is true on org.apache.ws.security.WSSConfig, this case is implemented the same way as the digest password case (since Apache CXF 2.4.0). Otherwise, an exception is thrown.
If no Password element is included in a received UsernameToken on the server side, the callback handler is not called (since Apache CXF 2.4.0).
DECRYPT
Need a password to retrieve a private key from a Java keystore, where WSPasswordCallback.getIdentifier() gives the alias of the keystore entry. WSS4J uses this private key to decrypt the session (symmetric) key.
SIGNATURE
Need a password to retrieve a private key from a Java keystore, where WSPasswordCallback.getIdentifier() gives the alias of the keystore entry. WSS4J uses this private key to produce a signature.
SECRET_KEY
Need a secret key for encryption or signature on the outbound side, or for decryption or verification on the inbound side. The callback handler must set the key using the setKey(byte[]) method.
SECURITY_CONTEXT_TOKEN
Need the key for a wsc:SecurityContextToken, which you provide by calling the setKey(byte[]) method.
CUSTOM_TOKEN
Need a token as a DOM element. For example, this is used for the case of a reference to a SAML Assertion or SecurityContextToken that is not in the message. The callback handler must set the token using the setCustomToken(Element) method.
KEY_NAME
(Obsolete) Since Apache CXF 2.4.0, this usage code is obsolete.
USERNAME_TOKEN_UNKNOWN
(Obsolete) Since Apache CXF 2.4.0, this usage code is obsolete.
UNKNOWN
Not used by WSS4J.