Writing SecurityEnvironmentHandlers for XWS-Security Applications

The signing and encryption operations require private-keys and certificates. An application can obtain such information in various ways, such as looking up a keystore with an alias, using the default key-pairs available with the container, looking up a truststore with an alias, etc. Similarly if an application wants to send a username-password in a UsernameToken, it can choose to obtain the username-password pair in various ways, such as reading from a file, prompting the user on the console, using a popup window, etc. The authentication of the username-password on the receiving application can similarly be done by plugging into existing authentication infrastructure, using a proprietary username-password database, etc.

To support these possibilities, XWS-Security defines a set of CallBack classes and requires the application to define a CallBackHandler to handle these callbacks. The xwss:SecurityEnvironmentHandler element is a compulsory child element that needs to be specified. The value of this element is the class name of a Java class that implements the javax.security.auth.callback.CallbackHandler interface and handles the set of callbacks defined by XWS-Security. There are a set of callbacks that are mandatory and every CallbackHandler needs to implement them. A few callbacks are optional and can be used to supply some fine-grained property information to the XWS-Security run-time.

Because information such as private keys and certificates for signing and encryption can be obtained in various ways (looking up a keystore with an alias, using the default key-pairs available with the container, looking up a truststore with an alias, etc.), every callback defines a set of Request inner classes and a callback can be initialized with any of its request inner classes. A tagging Request interface is also defined within the callback to tag all Request classes. For example, the XWS-Security configuration schema defines an xwss:X509Token element containing an optional attribute certificateAlias. When the xwss:X509Token element embedded inside a xwss:Sign element has a certificateAlias attribute specified as shown in the following code snippet, the XWS-Security run-time would invoke the SecurityEnvironmentHandler of the application with a SignatureKeyCallback object to obtain the private-key required for the signing operation.

The SignatureKeyCallback will be initialized by XWS-Security run-time with an AliasPrivKeyCertRequest in the following manner:

The application's SecurityEnvironmentHandler implementation then needs to handle the SignatureKeyCallback and use the alias to locate and set the private-key and X.509 certificate pair on the AliasPrivKeyCertRequest. The following code shows how this callback is handled in the handle() method of SecurityEnvironmentHandler shipped with the simple sample.

This handler uses a keystore to locate the private key and certificate pair, and sets it using AliasPrivKeyCertRequest.

As shown in the sample code, the SecurityEnvironmentHandler should throw an UnsupportedCallbackException whenever it cannot handle a Callback or a particular Request type of a Callback.

The type of Request with which the Callback is initialized often depends on the information specified in the security configuration file of the application. For example if the xwss:X509Token specified under an xwss:Sign element did not contain the certificateAlias attribute, XWS-Security would invoke the application's SecurityEnvironmentHandler with SignatureKeyCallback.DefaultPrivKeyCertRequest to try and obtain the default private-key and certificate pair. If the SecurityEnvironmentHandler does not handle this request and throws an UnsupportedCallbackException, the signature operation would fail.

For more information, read the API documentation for callbacks from the <JWSDP_HOME>/xws-security/docs/api/com/sun/xml/wss/impl/callback/package-summary.html. This documentation includes the list of mandatory and optional callbacks and the details of the Callback classes and supported methods. Table 3-24 provides a brief summary of all the mandatory Callback classes and their associated Request types.

Table 3-24 Summary of Callback classes and their Request types
Callback	Description	Request Inner Classes Defined	Methods in the Request Classes
Signature Key Callback	Used by XWS-Security run-time to obtain the private key to be used for signing the corresponding X.509 certificate. There are two ways in which an application can supply the private-key and certificate information. 1. Lookup a keystore using an alias. 2. Obtain the default private-key and certificate from the container/environment in which the application is running. Accordingly, there are two `Request` inner classes with which the `SignatureKeyCallback` can be initialized.	1. `AliasPrivKeyCertRequest`: A `Callback` initialized with this request should be handled if the private key to be used for signing is mapped to an alias. 2. `DefaultPrivKeyCertRequest`: A `Callback` initialized with this request should be handled if there's some default private key to be used for signing.	The following four methods are present in all `Request` Classes of this `Callback`: `public void setPrivateKey( PrivateKey privateKey) public PrivateKey getPrivateKey()` `public void setX509Certificate( X509Certificate certificate) public X509Certificate getX509Certificate()`
Signature Verification Key Callback	Obtains the certificate required for signature verification. There are currently two situations in which XWS-Security would require this Callback to resolve the certificate: 1. When the signature to be verified references the key using an X.509 `SubjectKeyIdentifier`. For example, when the sender specifies the attribute `xwss:keyReferenceType="Identifier"` on the `xwss:X509Token` child of the `xwss:Sign` element. 2. When the signature to be verified references the key using an X.509 `IssuerSerialNumber`. For example, when the sender specifies the attribute `xwss:keyReferenceType="IssuerSerialNumber"` on the `xwss:X509Token` child of the `xwss:Sign` element. Accordingly, there are two `Request` inner classes with which a `SignatureVerificationKeyCallback` can be initialized. Note: Additional `Requests` may be defined in a future release.	1. `X509SubjectKeyIdentifierBasedRequest`: Request for an X.509 certificate whose X.509 `SubjectKeyIdentifier` value is given. 2. `X509IssuerSerialBasedRequest`: Request for an X.509 certificate whose issuer name and serial number values are given.	The following two methods are present in all the `Request` classes of this `Callback`: `public void setX509Certificate( X509Certificate certificate)` `public X509Certificate getX509Certificate()`
Encryption Key Callback	Obtains the certificate for key-encryption or a symmetric-key for data encryption. There are currently three situations in which XWS-Security would require this `Callback` for performing encryption: 1. When the `xwss:Encrypt` element contains an `xwss:X509Token` child with `certificateAlias` attribute set to an alias. The `certificateAlias` indicates that a random symmetric key is used for encryption of the specified message part and the certificate is then used to encrypt the random symmetric-key to be sent along with the message. 2. When the `xwss:Encrypt` element contains an `xwss:X509Token` child with no `certificateAlias` attribute set on it. XWS-Security tries to obtain a default certificate from the `Callback` to be used for encrypting the random symmetric key. 3. When the `xwss:Encrypt` element contains an `xwss:SymmetricKey` child specifying the `keyAlias` attribute. This alias indicates that a symmetric key corresponding to this alias needs to be located and used for encryption of the specified message part. Accordingly, there are three `Request` inner classes with which an `EncryptionKeyCallback` can be initialized.	1. `AliasX509CertificateRequest`: A `Callback` initialized with this request should be handled if the X.509 certificate to be used for encryption is mapped to an alias. 2. `DefaultX509CertificateRequest`: A `Callback` initialized with this request should be handled if there's a default X.509 certificate to be used for encryption. 3. `AliasSymmetricKeyRequest`: A `Callback` initialized with this request should be handled if the symmetric key to be used for encryption is mapped to an alias.	The following two methods are present in the `AliasX509CertificateRequest` and `DefaultX509CertificateRequest Request` classes of this `Callback`: `public void setX509Certificate( X509Certificate certificate) public X509Certificate getX509Certificate()` The following methods are present in the `AliasSymmetricKeyRequest` class of this `Callback`: `public void setSymmetricKey( javax.crypto.SecretKey symmetricKey) public javax.crypto.SecretKey getSymmetricKey()`
Decryption Key Callback	Obtains the symmetric key to be used for decrypting the encrypted data or obtaining the private-key for decrypting the encrypted random symmetric key that was sent with the message (along with the encrypted data). There are currently four situations in which XWS-Security will require this `Callback` to perform decryption. 1. When the `EncryptedKey` references the key (used for encrypting the symmetric key) using an X.509 `SubjectKeyIdentifier`. For example, when the sender specifies the attribute `keyReferenceType="Identifier"` on the `xwss:X509Token` child of the `xwss:Encrypt` element. 2. When the `EncryptedKey` references the key (used for encrypting the symmetric key) using an X.509 `IssuerSerialNumber`. For example, when the sender specifies the attribute `keyReferenceType="IssuerSerialNumber"` on the `xwss:x509Token` child of `xwss:Encrypt` element.	1. `X509SubjectKeyIdentifierBasedRequest`: Request for a private-key when the X.509 `SubjectKeyIdentifier` value for a corresponding X.509 certificate is given. 2. `X509IssuerSerialBasedRequest`: Request for a private key when the issuer name and serial number values for a corresponding X.509 certificate are given. 3. `X509CertificateBasedRequest`: Request for a private key when a corresponding X.509 certificate is given.	The following two methods are present in the `X509SubjectKeyIdentifierBasedRequest`, `X509IssuerSerialBasedRequest`, and `X509CertificateBasedRequest` `Request` classes of this `Callback`: `public void setPrivateKey( PrivateKey privateKey) public PrivateKey getPrivateKey()`
Decryption Key Callback (continued)	3. When the `EncryptedKey` contains a `wsse:Direct` reference to the key used for encrypting the symmetric key. This means the X.509 certificate is present as a `wsse:BinarySecurityToken` in the message. For example, when the sender specifies the attribute `keyReferenceType="Direct"` on the `xwss:x509Token` child of `xwss:Encrypt` element. 4. When the `EncryptedData` contains a `ds:keyName` reference to the symmetric key that was used for encryption. For example, when the sender specifies the `xwss:SymmetricKey` child of `xwss:Encrypt` and specifies the `keyAlias` attribute on it. Accordingly, there are four `Request` classes with which a `DecryptionKeyCallback` can be initialized.	4. `AliasSymmetricKeyRequest`: A `Callback` initialized with this request should be handled if the symmetric key to be used for decryption is mapped to some alias.	The following methods are present in the `AliasSymmetricKeyRequest` class of this `Callback`: `public void setSymmetricKey( javax.crypto.SecretKey symmetricKey) public javax.crypto.SecretKey getSymmetricKey()`
Password Validation Callback	Username-Password validation. A validator that implements the `PasswordValidator` interface should be set on the callback by the callback handler. There are currently two situations in which XWS-Security will require this `Callback` to perform username-password validation: 1. When the receiver gets a `UsernameToken` with plain-text user name and password. 2. When the receiver gets a `UsernameToken` with a digested password (as specified in the WSS UsernameToken Profile). Accordingly there are two Request classes with which the `PasswordValidationCallback` can be initialized. Note: A validator for WSS Digested Username-Password is provided as part of this callback, with classname `PasswordValidationCallback`.`DigestPasswordValidator`. This class implements WSS digest password validation. The method for computing password digest is described in `http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-username-token-profile-1.0.pdf`. For more information, see the `ServerSecurityEnvironmentHandler` in <`JWSDP_HOME`>`/xws-security/samples/jaas-sample/src/com/sun/xml/wss/sample`.	1. `PlainTextPasswordRequest`: Represents a validation request when the password in the username token is in plain text. 2. `DigestPasswordRequest`: Represents a validation request when the password in the username token is in digested form.	The following methods are present in the `PlainTextPasswordRequest`: `public String getUsername()` `public String getPassword()` The following methods are present in the `DigestPasswordRequest`: `public void setPassword(String password)` This method must be invoked by the `CallbackHandler` while handling a `Callback` initialized with `DigestPasswordRequest` to set the plain-text password on the `Callback`. `public java.lang.String getPassword()` `public java.lang.String getUsername()` `public java.lang.String getDigest()` `public java.lang.String getNonce()` `public java.lang.String getCreated()`
Username Callback	To supply the user name for the `UsernameToken` at run-time. It contains the following two methods: `public void setUsername(` `String username)` `public String getUsername()` Refer to the `ClientSecurityEnvironmentHandler` of the `jaas-sample` sample located in <`JWSDP_HOME`>`/xws-security/samples/jaas-sample/src/com/sun/xml/wss/sample` for more details on using the `UsernameCallback`.
PasswordCallback	To supply the password for the username token at run-time. It contains the following two methods: `public void setPassword(String password)` `public String getPassword()` Refer to the `ClientSecurityEnvironmentHandler` of the `jaas-sample` sample located in <`JWSDP_HOME`>`/xws-security/samples/jaas-sample/src/com/sun/xml/wss/sample` for more details on using the `PasswordCallback`.
Property Callback	Optional callback to specify the values of properties configurable with XWS-Security run-time. Refer to the API documentation at `<JWSDP_HOME>/xws-security/docs/api/com/sun/xml/wss/impl/callback/PropertyCallback.html` for a list of configurable properties methods supported by this callback.
Prefix Namespace Mapping Callback	Optional callback to register any prefix versus namespace-uri mappings that the developer wants to make use of in the security configuration (while specifying `Targets` as `xpaths`). Refer to the API documentation at `<JWSDP_HOME>/xws-security/docs/api/com/sun/xml/wss/impl/callback/PrefixNamespaceMappingCallback.html` for more details.

The following code snippet shows the handle() method skeleton for an application's SecurityEnvironmentHandler that handles all the mandatory Callbacks (except UsernameCallback and PasswordCallback) and associated Requests defined by XWS-Security. A particular application may choose to throw an UnsupportedCallbackException for any of the Callbacks or its Requests that it cannot handle. The UsernameCallback and PasswordCallback are useful for obtaining a username-password pair at run-time and are explained later in this section.

Note: In this release of XWS-Security, users will have to ensure that the SecurityEnvironmentHandler implementation they supply is thread safe.

An application can also choose not to handle certain callbacks if it knows that the particular application will never require those callbacks. For example if the security application only deals with signing the requests and does not deal with encryption or username tokens, its handle() method only needs to worry about SignatureKeyCallback (with its associated Requests) and SignatureVerificationKeyCallback (with its associated Requests). It can then throw an UnsupportedCallbackException for any other callback. The following code shows the handle() method skeleton for such an application:

Similarly, an application dealing only with UsernameToken but not signature or encryption requirements can simply throw UnsupportedCallbackException for all non-username related callbacks.

The SecurityEnvironmentHandler implementation for the simple sample is located in the directory <JWSDP_HOME>/xws-security/samples/simple/src/com/sun/xml/wss/sample. The simple sample uses the same SecurityEnvironmentHandler for both the client and server side.

The jaas-sample sample requires a different set of callbacks to be handled on the client and server side. The CallbackHandlers for the jaas-sample sample are located in the directory <JWSDP_HOME>/xws-security/samples/jaas-sample/src/com/sun/xml/wss/sample. The two CallbackHandlers defined for the jaas-sample are:

Using the SubjectAccessor API

XWS-Security applications might require access to the authenticated subject of the sender from within the SEI implementation methods. The SubjectAccessor API contains a single method:

This method returns the Subject if one is available or else it returns NULL. The context argument to be passed into this method is the ServletEndpointContext which is available with the SEI implementation class. For an example on how the SubjectAccessor is used to obtain the authenticated sender subject, refer to the PingImpl.java class in the jaas-sample sample located at <JWSDP_HOME>/xws-security/samples/jaas-sample/server/src/sample. The API for SubjectAccessor viewed from <JWSDP_HOME>/xws-security/docs/api/com/sun/xml/wss/SubjectAccessor.html.