public String getLoginUrl() {
        return loginUrl;
    }
Returns the login URL used to authenticate a user.
<p/>
Most Shiro filters use this url
as the location to redirect a user when the filter requires authentication.  Unless overridden, the
{@link #DEFAULT_LOGIN_URL DEFAULT_LOGIN_URL} is assumed, which can be overridden via
{@link #setLoginUrl(String) setLoginUrl}.

@return the login URL used to authenticate a user, used when redirecting users if authentication is required.
web/src/main/java/org/apache/shiro/web/filter/AccessControlFilter.java