public void setUnauthorizedUrl(String unauthorizedUrl) {
        this.unauthorizedUrl = unauthorizedUrl;
    }
Sets the URL to which users should be redirected if they are denied access to an underlying path or resource.
<p/>
If the value is {@code null} a raw {@link HttpServletResponse#SC_UNAUTHORIZED} response will
be issued (401 Unauthorized), retaining default web server behavior.
<p/>
Unless overridden by calling this method, the default value is {@code null}.  If desired, you can specify a
meaningful path within your application if you would like to show the user a 'nice' page in the event of
unauthorized access.

@param unauthorizedUrl the URL to which users should be redirected if they are denied access to an underlying
                       path or resource, or {@code null} to an ensure raw
                       {@link HttpServletResponse#SC_UNAUTHORIZED} response is issued (401 Unauthorized).
web/src/main/java/org/apache/shiro/web/filter/authz/AuthorizationFilter.java