This Callback is intended for Username-Password validation.
A validator that implements the PasswordValidator interface
should be set on the callback by the callback handler.
Note: A validator for WSS Digested Username-Password is provided
as part of this callback.
author: XWS-Security Team
Inner Class :public static interface Request
Inner Class :public static class PlainTextPasswordRequest implements Request
Inner Class :public static class DigestPasswordRequest implements Request
Inner Class :public static interface PasswordValidator
Inner Class :public static class DigestPasswordValidator implements PasswordValidator
Inner Class :public static class PasswordValidationException extends Exception