Just add this to your web.xml:

<login-config>
    <auth-method>FORM</auth-method>
    <realm-name>myrealm</realm-name>
    <form-login-config>
      <form-login-page>login</form-login-page>
      <form-error-page>loginfailed</form-error-page>
    </form-login-config>
</login-config> 

Your form needs to have these inputs and action:

<form method="POST"  action="j_security_check" >
 <input type="text"  name="j_username" >
 <input type="password"  name="j_password" >
</form>