Form based JAAS - How to implement login system explicitly, outside the container?

[Vladimir Razov]

I have configured form based JAAS in my app. Basically, in web.xml I have declared security constraints on certain jsp page, declared specific roles, login and error pages.
So, my login form is:

<form id="loginForm" action="j_security_check" method="post">
        <p>
            <label for="name">Username</label> <input name="j_username"
                id="username" type="text" required/>
        </p>
        <p>
            <label for="password">Password</label> <input name="j_password"
                id="password" type="text" required/>
        </p>

            <input type="submit" value="Submit" />
</form>

This works fine when some user tries to access some of the pages declared in <security-constraint> tag of web.xml.
Container automatically manages login process, redirects to login page and if login details are valid, gives access to secured page.

Now, how should I implement login system so that user can go to login page (possibly same login form) and log in from there?

[Vladimir Razov]

Well, that's how form based authentication works .
Form's action="j_security_check" sends form field values to container, which handles login process and forwards to asked/secured page (or servlet) if login succeeds.

I was thinking to use this login form "explicitly": just to go to this page, enter login details and press Submit button. But, as I understood, that can't be done when using form based security.

So, I have implemented this like: when user wants to login, user clicks on login link somewhere on the page, which is a link to secured, user account details jsp page.