/*
 * Copyright (c) 2020, 2021 Contributors to Eclipse Foundation. All rights reserved.
 * Copyright (c) 1997, 2020 Oracle and/or its affiliates and others.
 * All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0, which is available at
 * http://www.eclipse.org/legal/epl-2.0.
 *
 * This Source Code may also be made available under the following Secondary
 * Licenses when the conditions for such availability set forth in the
 * Eclipse Public License v. 2.0 are satisfied: GNU General Public License,
 * version 2 with the GNU Classpath Exception, which is available at
 * https://www.gnu.org/software/classpath/license.html.
 *
 * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
 */

package jakarta.security.auth.message;

import javax.security.auth.Subject;

/**
 * An implementation of this interface is used to validate received service request messages, and to secure service
 * response messages.
 *
 * @see MessageInfo
 * @see Subject
 */
public interface ServerAuth {

    /**
     * Authenticate a received service request.
     *
     * <p>
     * This method is called to transform the mechanism-specific request message acquired by calling getRequestMessage (on
     * messageInfo) into the validated application message to be returned to the message processing runtime. If the received
     * message is a (mechanism-specific) meta-message, the method implementation must attempt to transform the meta-message
     * into a corresponding mechanism-specific response message, or to the validated application request message. The
     * runtime will bind a validated application message into the the corresponding service invocation.
     *
     * <p>
     * This method conveys the outcome of its message processing either by returning an AuthStatus value or by throwing an
     * AuthException.
     *
     * @param messageInfo A contextual object that encapsulates the client request and server response objects, and that may
     * be used to save state across a sequence of calls made to the methods of this interface for the purpose of completing
     * a secure message exchange.
     *
     * @param clientSubject A Subject that represents the source of the service request. It is used by the method
     * implementation to store Principals and credentials validated in the request.
     *
     * @param serviceSubject A Subject that represents the recipient of the service request, or null. It may be used by the
     * method implementation as the source of Principals or credentials to be used to validate the request. If the Subject
     * is not null, the method implementation may add additional Principals or credentials (pertaining to the recipient of
     * the service request) to the Subject.
     *
     * @return An AuthStatus object representing the completion status of the processing performed by the method. The
     * AuthStatus values that may be returned by this method are defined as follows:
     *
     * <ul>
     *   <li>AuthStatus.SUCCESS when the application request message was successfully validated. The validated request message
     *       is available by calling getRequestMessage on messageInfo.
     *
     *   <li>AuthStatus.SEND_SUCCESS to indicate that validation/processing of the request message successfully produced the
     *       secured application response message (in messageInfo). The secured response message is available by calling
     *       getResponseMessage on messageInfo.
     *
     *    <li>AuthStatus.SEND_CONTINUE to indicate that message validation is incomplete, and that a preliminary response was
     *        returned as the response message in messageInfo.
     *
     *        When this status value is returned to challenge an application request message, the challenged request must be saved
     *        by the authentication module such that it can be recovered when the module's validateRequest message is called to
     *        process the request returned for the challenge.
     *
     *   <li>AuthStatus.SEND_FAILURE to indicate that message validation failed and that an appropriate failure response
     *       message is available by calling getResponseMessage on messageInfo.
     * </ul>
     *
     * @exception AuthException When the message processing failed without establishing a failure response message (in
     * messageInfo).
     */
    AuthStatus validateRequest(MessageInfo messageInfo, Subject clientSubject, Subject serviceSubject) throws AuthException;

    /**
     * Secure a service response before sending it to the client.
     *
     * This method is called to transform the response message acquired by calling getResponseMessage (on messageInfo) into
     * the mechanism-specific form to be sent by the runtime.
     * <p>
     * This method conveys the outcome of its message processing either by returning an AuthStatus value or by throwing an
     * AuthException.
     *
     * @param messageInfo A contextual object that encapsulates the client request and server response objects, and that may
     * be used to save state across a sequence of calls made to the methods of this interface for the purpose of completing
     * a secure message exchange.
     *
     * @param serviceSubject A Subject that represents the source of the service response, or null. It may be used by the
     * method implementation to retrieve Principals and credentials necessary to secure the response. If the Subject is not
     * null, the method implementation may add additional Principals or credentials (pertaining to the source of the service
     * response) to the Subject.
     *
     * @return An AuthStatus object representing the completion status of the processing performed by the method. The
     * AuthStatus values that may be returned by this method are defined as follows:
     *
     * <ul>
     *   <li>AuthStatus.SEND_SUCCESS when the application response message was successfully secured. The secured response
     *       message may be obtained by calling getResponseMessage on messageInfo.
     *
     *   <li>AuthStatus.SEND_CONTINUE to indicate that the application response message (within messageInfo) was replaced with
     *       a security message that should elicit a security-specific response (in the form of a request) from the peer.
     *
     *       This status value serves to inform the calling runtime that (to successfully complete the message exchange) it will
     *       need to be capable of continuing the message dialog by processing at least one additional request/response exchange
     *       (after having sent the response message returned in messageInfo).
     *
     *       When this status value is returned, the application response must be saved by the authentication module such that it
     *       can be recovered when the module's validateRequest message is called to process the elicited response.
     *
     *   <li>AuthStatus.SEND_FAILURE to indicate that a failure occurred while securing the response message and that an
     *       appropriate failure response message is available by calling getResponseMeessage on messageInfo.
     * </ul>
     *
     * @exception AuthException When the message processing failed without establishing a failure response message (in
     * messageInfo).
     */
    default AuthStatus secureResponse(MessageInfo messageInfo, Subject serviceSubject) throws AuthException {
        return AuthStatus.SEND_SUCCESS;
    }

    /**
     * Remove method specific principals and credentials from the subject.
     *
     * @param messageInfo a contextual object that encapsulates the client request and server response objects, and that may
     * be used to save state across a sequence of calls made to the methods of this interface for the purpose of completing
     * a secure message exchange.
     *
     * @param subject the Subject instance from which the Principals and credentials are to be removed.
     *
     * @exception AuthException If an error occurs during the Subject processing.
     */
    default void cleanSubject(MessageInfo messageInfo, Subject subject) throws AuthException {

    }

}
