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009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
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018 */
019package org.apache.shiro.authz;
022 * A Permission represents the ability to perform an action or access a resource.  A Permission is the most
023 * granular, or atomic, unit in a system's security policy and is the cornerstone upon which fine-grained security
024 * models are built.
025 * <p/>
026 * It is important to understand a Permission instance only represents functionality or access - it does not grant it.
027 * Granting access to an application functionality or a particular resource is done by the application's security
028 * configuration, typically by assigning Permissions to users, roles and/or groups.
029 * <p/>
030 * Most typical systems are what the Shiro team calls <em>role-based</em> in nature, where a role represents
031 * common behavior for certain user types.  For example, a system might have an <em>Aministrator</em> role, a
032 * <em>User</em> or <em>Guest</em> roles, etc.
033 * <p/>
034 * But if you have a dynamic security model, where roles can be created and deleted at runtime, you can't hard-code
035 * role names in your code.  In this environment, roles themselves aren't aren't very useful.  What matters is what
036 * <em>permissions</em> are assigned to these roles.
037 * <p/>
038 * Under this paradigm, permissions are immutable and reflect an application's raw functionality
039 * (opening files, accessing a web URL, creating users, etc).  This is what allows a system's security policy
040 * to be dynamic: because Permissions represent raw functionality and only change when the application's
041 * source code changes, they are immutable at runtime - they represent 'what' the system can do.  Roles, users, and
042 * groups are the 'who' of the application.  Determining 'who' can do 'what' then becomes a simple exercise of
043 * associating Permissions to roles, users, and groups in some way.
044 * <p/>
045 * Most applications do this by associating a named role with permissions (i.e. a role 'has a' collection of
046 * Permissions) and then associate users with roles (i.e. a user 'has a' collection of roles) so that by transitive
047 * association, the user 'has' the permissions in their roles.  There are numerous variations on this theme
048 * (permissions assigned directly to users, or assigned to groups, and users added to groups and these groups in turn
049 * have roles, etc, etc).  When employing a permission-based security model instead of a role-based one, users, roles,
050 * and groups can all be created, configured and/or deleted at runtime.  This enables  an extremely powerful security
051 * model.
052 * <p/>
053 * A benefit to Shiro is that, although it assumes most systems are based on these types of static role or
054 * dynamic role w/ permission schemes, it does not require a system to model their security data this way - all
055 * Permission checks are relegated to {@link org.apache.shiro.realm.Realm} implementations, and only those
056 * implementations really determine how a user 'has' a permission or not.  The Realm could use the semantics described
057 * here, or it could utilize some other mechanism entirely - it is always up to the application developer.
058 * <p/>
059 * Shiro provides a very powerful default implementation of this interface in the form of the
060 * {@link org.apache.shiro.authz.permission.WildcardPermission WildcardPermission}.  We highly recommend that you
061 * investigate this class before trying to implement your own <code>Permission</code>s.
062 *
063 * @see org.apache.shiro.authz.permission.WildcardPermission WildcardPermission
064 * @since 0.2
065 */
066public interface Permission {
068    /**
069     * Returns {@code true} if this current instance <em>implies</em> all the functionality and/or resource access
070     * described by the specified {@code Permission} argument, {@code false} otherwise.
071     * <p/>
072     * <p>That is, this current instance must be exactly equal to or a <em>superset</em> of the functionalty
073     * and/or resource access described by the given {@code Permission} argument.  Yet another way of saying this
074     * would be:
075     * <p/>
076     * <p>If &quot;permission1 implies permission2&quot;, i.e. <code>permission1.implies(permission2)</code> ,
077     * then any Subject granted {@code permission1} would have ability greater than or equal to that defined by
078     * {@code permission2}.
079     *
080     * @param p the permission to check for behavior/functionality comparison.
081     * @return {@code true} if this current instance <em>implies</em> all the functionality and/or resource access
082     *         described by the specified {@code Permission} argument, {@code false} otherwise.
083     */
084    boolean implies(Permission p);