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  * Licensed to the Apache Software Foundation (ASF) under one

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  * 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 org.apache.shiro.authz;

 /**

  * A Permission represents the ability to perform an action or access a resource.  A Permission is the most

  * granular, or atomic, unit in a system's security policy and is the cornerstone upon which fine-grained security

  * models are built.

  * <p/>

  * It is important to understand a Permission instance only represents functionality or access - it does not grant it.

  * Granting access to an application functionality or a particular resource is done by the application's security

  * configuration, typically by assigning Permissions to users, roles and/or groups.

  * <p/>

  * Most typical systems are what the Shiro team calls <em>role-based</em> in nature, where a role represents

  * common behavior for certain user types.  For example, a system might have an <em>Aministrator</em> role, a

  * <em>User</em> or <em>Guest</em> roles, etc.

  * <p/>

  * But if you have a dynamic security model, where roles can be created and deleted at runtime, you can't hard-code

  * role names in your code.  In this environment, roles themselves aren't aren't very useful.  What matters is what

  * <em>permissions</em> are assigned to these roles.

  * <p/>

  * Under this paradigm, permissions are immutable and reflect an application's raw functionality

  * (opening files, accessing a web URL, creating users, etc).  This is what allows a system's security policy

  * to be dynamic: because Permissions represent raw functionality and only change when the application's

  * source code changes, they are immutable at runtime - they represent 'what' the system can do.  Roles, users, and

  * groups are the 'who' of the application.  Determining 'who' can do 'what' then becomes a simple exercise of

  * associating Permissions to roles, users, and groups in some way.

  * <p/>

  * Most applications do this by associating a named role with permissions (i.e. a role 'has a' collection of

  * Permissions) and then associate users with roles (i.e. a user 'has a' collection of roles) so that by transitive

  * association, the user 'has' the permissions in their roles.  There are numerous variations on this theme

  * (permissions assigned directly to users, or assigned to groups, and users added to groups and these groups in turn

  * have roles, etc, etc).  When employing a permission-based security model instead of a role-based one, users, roles,

  * and groups can all be created, configured and/or deleted at runtime.  This enables  an extremely powerful security

  * model.

  * <p/>

  * A benefit to Shiro is that, although it assumes most systems are based on these types of static role or

  * dynamic role w/ permission schemes, it does not require a system to model their security data this way - all

  * Permission checks are relegated to {@link org.apache.shiro.realm.Realm} implementations, and only those

  * implementations really determine how a user 'has' a permission or not.  The Realm could use the semantics described

  * here, or it could utilize some other mechanism entirely - it is always up to the application developer.

  * <p/>

  * Shiro provides a very powerful default implementation of this interface in the form of the

  * {@link org.apache.shiro.authz.permission.WildcardPermission WildcardPermission}.  We highly recommend that you

  * investigate this class before trying to implement your own <code>Permission</code>s.

  *

  * @see org.apache.shiro.authz.permission.WildcardPermission WildcardPermission

  * @since 0.2

  */

 public interface Permission {

     /**

      * Returns {@code true} if this current instance <em>implies</em> all the functionality and/or resource access

      * described by the specified {@code Permission} argument, {@code false} otherwise.

      * <p/>

      * <p>That is, this current instance must be exactly equal to or a <em>superset</em> of the functionalty

      * and/or resource access described by the given {@code Permission} argument.  Yet another way of saying this

      * would be:

      * <p/>

      * <p>If &quot;permission1 implies permission2&quot;, i.e. <code>permission1.implies(permission2)</code> ,

      * then any Subject granted {@code permission1} would have ability greater than or equal to that defined by

      * {@code permission2}.

      *

      * @param p the permission to check for behavior/functionality comparison.

      * @return {@code true} if this current instance <em>implies</em> all the functionality and/or resource access

      *         described by the specified {@code Permission} argument, {@code false} otherwise.

      */

     boolean implies(Permission p);

 }