Is there any way to do this in PHP (or with a combination of JS)?

[immediate]

There's a login form on page A: http://www.example.com/A.html

The 'action' attribute of which is: action="/B.html"

So when someone logs in with the form on A.html, the data will be submitted to / visitor redirected to B.html.

Now what I want is: there's an <iframe></iframe> on /C.html, framing B.html, is there any way so that when someone logs in with the form on A.html, the visitor is redirected to C.html and the login details is submitted to B.html that's framed on C.html in the <iframe></iframe>? So after the person logs in from A.html, he arrives at C.html with the actual CP dashboard framed in an <iframe>.

I have absolutely no clue in achieving this. Maybe the form will be submitted to C.html first and C.html submits the login details to B.html (framed in C.html) via JavaScript? How?

[phpmymirror]

You mean passing variables between javascript on different frames?

yes its possible, most browsers dont support this due to security risks

[seoexpert22]

You can try different browser , must be install javascript in your computer

[enjoibp3]

One way I've been passing variables to lightbox is to use the $_GET[]; instead of $_POST[]; so when you login still post those variables but when you get to c.html make the iframe tag

<iframe src="http://b.php?user=$_POST['username']&pass=$_POST['pass']"></iframe>

Then on b.php grab the variables from the QUERY string like this
$_GET['user'];
$_GET['pass'];

That will atleast pass those variables to the iframe for you I'm not sure where you want it to go from there.

P.S. passing usernames and passwords through URL strings could be a risky idea so you can encode the url with base64_encode(); so it would go

$user = base64_encode($_POST['username']);
$pass = base64_encode($_POST['password']);

<iframe src="b.php?user=<?php echo $user; ?>&pass=<?php echo $pass; ?>"></iframe>

Then in B.php use base64_decode(); like so
$username = base64_decode($_GET['user']);
$pass = base64_decode($_GET['pass']);

None of this is tested I'm just going off what I have done in the past for similar situations.

[theuman]

Why use JS??

why not redirect them using the header tags?

header("Location: usercp.php"); 

And set up some cookies too