Laravel 5: how to redirect with data to external resource form controller

I want to send user to payment gate. Normally it could be made by this form:

<form method="post" action="http://ift.tt/1GKW92t">
    <input type="hidden" name="MNT_ID" value="12345678">
    <input type="hidden" name="MNT_TRANSACTION_ID" value="000001">
    <input type="hidden" name="MNT_CURRENCY_CODE" value="USD">
    <input type="hidden" name="MNT_AMOUNT" value="123.45">
    <input type="submit" value="Pay">
</form>

User press "Pay" and redirect to payment gate.

But I want implement this workflow:

1. User enter delivery info, payment method, etc.
2. After that he press "Pay" and
3. First I want to store data (I do it in my controller)...
4. ... and after that I want redirect user to payment gate. (this is unclear for me)

The question is: how to redirect user to external resource from controller (method should be POST, and I need do send some data such as MNT_ID, etc. (see form example above)?

via Chebli Mohamed