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📁 java安全－论证授权
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<td bgcolor="ffffff" width="15">&nbsp;</td><td bgcolor="ffffff" width="12">&nbsp;</td><td valign="top" align="left" bgcolor="ffffff" width="*">
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<td width="90%"><font size="4" face="Verdana, Arial, Helvetica"><b>概述</b></font></td><td width="200" align="right"><font size="1" face="Verdana, Arial, Helvetica"><nobr>   第 1 页（共9 页）</nobr></font></td>
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<p>了解 Java 平台如何实现授权的访问控制对于了解我们将在本章中讨论的概念很重要。Java
平台使用<i>访问控制环境（access control context）</i>的概念来确定当前执行线程的权限。
从概念上讲，可以将它视作与每个执行线程连接的令牌。
在 JAAS 之前，访问控制基于了解当前 Java .class 文件的代码来源或数字签名者的身份。在这种模型下，
访问控制是基于了解代码出自于何处。有了 JAAS，我们将模型转了个向。通过将 <code>Subject</code> 添加到访问控制环境，
我们可以开始根据谁正在执行（或要求执行）一段给定代码来授予或拒绝访问权。</p>
<p>在本章中，您将了解 JAAS 的用于控制对敏感代码访问的机制。
我们将首先描述授权在 JAAS 中是如何工作的，然后继续更深入地描述授权框架的每个组件。
在本章的最后，我们将给出在较大型的运行示例中使用的一些代码样本，它们演示了程序性授权和声明性授权技术。
读完本章之后，您应该清楚地知道 JAAS 的认证和授权机制如何一起工作来保护基于 Java 的系统。</p>
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