Unlimited form data can be captured at the point of signup. This is useful if you need to pass other data to the system. For this to work,
add hidden form boxes within the form field. The name of the input boxes isn't important. An example:
<input type="hidden" name="some_field_name" value="my value">
<input type="hidden" name="some_other_field_name" value="my other value">
The form fields must NOT contain the same names as the required fields above.
For the GET method, arrays are also supported.
<input type="hidden" name="arr[ayumi]" value="hamasaki">
<input type="hidden" name="arr[koda]" value="kumi">