protected String getRedirectUrl(ServletRequest request, ServletResponse response, Subject subject) {
        return getRedirectUrl();
    }
Returns the redirect URL to send the user after logout.  This default implementation ignores the arguments and
returns the static configured {@link #getRedirectUrl() redirectUrl} property, but this method may be overridden
by subclasses to dynamically construct the URL based on the request or subject if necessary.
<p/>
Note: the Subject is <em>not</em> yet logged out at the time this method is invoked.  You may access the Subject's
session if one is available and if necessary.
<p/>
Tip: if you need to access the Subject's session, consider using the
{@code Subject.}{@link Subject#getSession(boolean) getSession(false)} method to ensure a new session
isn't created unnecessarily. If a session was created, it will be immediately stopped after logout,
not providing any value and unnecessarily taxing session infrastructure/resources.

@param request  the incoming Servlet request
@param response the outgoing ServletResponse
@param subject  the not-yet-logged-out currently executing Subject
@return the redirect URL to send the user after logout.
web/src/main/java/org/apache/shiro/web/filter/authc/LogoutFilter.java