Manages thread-state for {@link Subject Subject} access (supporting {@code SecurityUtils.}{@link hunt.shiro.SecurityUtils#getSubject() getSubject()} calls) during a thread's execution. <p/> The {@link #bind bind} method will bind a {@link Subject} and a {@link hunt.shiro.mgt.SecurityManager SecurityManager} to the {@link ThreadContext} so they can be retrieved from the {@code ThreadContext} later by any {@code SecurityUtils.}{@link hunt.shiro.SecurityUtils#getSubject() getSubject()} calls that might occur during the thread's execution.