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/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package io.milton.principal;

import javax.xml.namespace.QName;

/**
 * Marker interface to identify those classes which can act as a Principal. This can be a user or a group
 * 
 * An absolute minimum requirement for a Principal is to be able to identify it, and
 * this is represented by the sole method on this interface which is getIdentifier.
 * 

 * Note that some Principals are defined by the webdav protocol so must be subject
 * to explicit processing requirements. For this reason the principle identifier
 * is a structured type which can be associated with a namespace and well known
 * names within that namespace.
 * 

 * 

 * There are 2 types of Principal
 * - Discrete: identifies a particular resource, which might be a user or group. Users are always discrete, groups may be
 * physical resources in which case they are represented as discrete resources. But groups may also be dynamically evaluated..
 * - DAV: a dynamically evaluated group as defined by the ACL spec. Eg the Authenticated group matches any user
 * with an authenticated request. A dynamically evaluated group defined by the protocol is not
 * a physical resource do does not have a corresponding href
 *
 * @author brad
 */
public interface Principal {

    /**
     * A means to identify the principle to webdav clients
     *
     * @return
     */
    PrincipleId getIdenitifer();

    /**
     * A principleId represents a unique identifier for a principle. It consists
     * of 2 parts;
     * - type
     * - value (optional)
     * 

     * The type says this identifier identifies a physical resource or some construct
     * defined by the ACL protocol. If the principal is a physical resource the
     * type will be a Qualified Name with a namespace of D: (ie webdav) and a local
     * name of href (which means the id is a href).
     * 

     * If the identifier identifies a protocol contruct the type will identify
     * which construct (which must be known to the protocol and hence to milton), such
     * as D:all, meaning all users
     * 

     * Eg
     * http://www.example.com/acl/groups/maintainers
     * For a specific user or group
     * 

     * or
     * 
     *   - for a group which represents all authenticated users, and is defined
     * by the DAV standard
     */
    interface PrincipleId {
        /**
         * Eg D:href or D:all
         *
         * @return
         */
        QName getIdType();

        /**
         * Eg null for an idType of "D:all", or http://blah.com/users/sam for "D:href"
         *
         * @return
         */
        String getValue();
    }
}