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 * http://www.apache.org/licenses/LICENSE-2.0
11 *
12 * Unless required by applicable law or agreed to in writing,
13 * software distributed under the License is distributed on an
14 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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;
20
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>Administrator</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 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 {
67
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 functionality
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 "permission1 implies permission2", 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 }