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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one
3    * or more contributor license agreements.  See the NOTICE file
4    * distributed with this work for additional information
5    * regarding copyright ownership.  The ASF licenses this file
6    * to you under the Apache License, Version 2.0 (the
7    * "License"); you may not use this file except in compliance
8    * with the License.  You may obtain a copy of the License at
9    *
10   *
11   *
12   * Unless required by applicable law or agreed to in writing,
13   * software distributed under the License is distributed on an
15   * KIND, either express or implied.  See the License for the
16   * specific language governing permissions and limitations
17   * under the License.
18   */
19  package org.apache.shiro.authz;
21  /**
22   * A Permission represents the ability to perform an action or access a resource.  A Permission is the most
23   * granular, or atomic, unit in a system's security policy and is the cornerstone upon which fine-grained security
24   * models are built.
25   * <p/>
26   * It is important to understand a Permission instance only represents functionality or access - it does not grant it.
27   * Granting access to an application functionality or a particular resource is done by the application's security
28   * configuration, typically by assigning Permissions to users, roles and/or groups.
29   * <p/>
30   * Most typical systems are what the Shiro team calls <em>role-based</em> in nature, where a role represents
31   * common behavior for certain user types.  For example, a system might have an <em>Aministrator</em> role, a
32   * <em>User</em> or <em>Guest</em> roles, etc.
33   * <p/>
34   * But if you have a dynamic security model, where roles can be created and deleted at runtime, you can't hard-code
35   * role names in your code.  In this environment, roles themselves aren't aren't very useful.  What matters is what
36   * <em>permissions</em> are assigned to these roles.
37   * <p/>
38   * Under this paradigm, permissions are immutable and reflect an application's raw functionality
39   * (opening files, accessing a web URL, creating users, etc).  This is what allows a system's security policy
40   * to be dynamic: because Permissions represent raw functionality and only change when the application's
41   * source code changes, they are immutable at runtime - they represent 'what' the system can do.  Roles, users, and
42   * groups are the 'who' of the application.  Determining 'who' can do 'what' then becomes a simple exercise of
43   * associating Permissions to roles, users, and groups in some way.
44   * <p/>
45   * Most applications do this by associating a named role with permissions (i.e. a role 'has a' collection of
46   * Permissions) and then associate users with roles (i.e. a user 'has a' collection of roles) so that by transitive
47   * association, the user 'has' the permissions in their roles.  There are numerous variations on this theme
48   * (permissions assigned directly to users, or assigned to groups, and users added to groups and these groups in turn
49   * have roles, etc, etc).  When employing a permission-based security model instead of a role-based one, users, roles,
50   * and groups can all be created, configured and/or deleted at runtime.  This enables  an extremely powerful security
51   * model.
52   * <p/>
53   * A benefit to Shiro is that, although it assumes most systems are based on these types of static role or
54   * dynamic role w/ permission schemes, it does not require a system to model their security data this way - all
55   * Permission checks are relegated to {@link org.apache.shiro.realm.Realm} implementations, and only those
56   * implementations really determine how a user 'has' a permission or not.  The Realm could use the semantics described
57   * here, or it could utilize some other mechanism entirely - it is always up to the application developer.
58   * <p/>
59   * Shiro provides a very powerful default implementation of this interface in the form of the
60   * {@link org.apache.shiro.authz.permission.WildcardPermission WildcardPermission}.  We highly recommend that you
61   * investigate this class before trying to implement your own <code>Permission</code>s.
62   *
63   * @see org.apache.shiro.authz.permission.WildcardPermission WildcardPermission
64   * @since 0.2
65   */
66  public interface Permission {
68      /**
69       * Returns {@code true} if this current instance <em>implies</em> all the functionality and/or resource access
70       * described by the specified {@code Permission} argument, {@code false} otherwise.
71       * <p/>
72       * <p>That is, this current instance must be exactly equal to or a <em>superset</em> of the functionalty
73       * and/or resource access described by the given {@code Permission} argument.  Yet another way of saying this
74       * would be:
75       * <p/>
76       * <p>If &quot;permission1 implies permission2&quot;, i.e. <code>permission1.implies(permission2)</code> ,
77       * then any Subject granted {@code permission1} would have ability greater than or equal to that defined by
78       * {@code permission2}.
79       *
80       * @param p the permission to check for behavior/functionality comparison.
81       * @return {@code true} if this current instance <em>implies</em> all the functionality and/or resource access
82       *         described by the specified {@code Permission} argument, {@code false} otherwise.
83       */
84      boolean implies(Permission p);
85  }