Hi Anand,
smpwservices.fcc is designed differently from smpwservicescgi.exe, but the function should be the same.
As an example, you can see USERNAME is not part of SMTOKEN, rather as parameter being passed by itself.
Location: /siteminderagent/forms/smpwservices.fcc?SMENC=UTF-8&SMTOKEN={RC2}aYviUhQX+TsCfn0zwVtH703N7TdjBlrY/PpCNf/P8kY8AcHmQxKv6wq6xN+yYWkZDbkjZ5tJpANLuPGtbkoyck251CvLTMfW&USERNAME=aduser&SMAUTHREASON=20&SMAGENTNAME=-SM-eMaalRWKPTzIEFgiaU0JBSdYY97z%2bP5pEWc5sMkoq2X6Py0jxvBjzYfKRywN5KRf&TARGET=-SM-http%3a%2f%2fliuho03--755%2eca%2ecom%2fadtest%2f
smpwservices.fcc file has at least 10 sections that fits use case "$$smauthreason$$ == 20", if this is customized page, make sure you modify the section that matched with your use case. Or try the default smpwservices.fcc file first.
If default smpwservices.fcc file still asks for entering USERNAME, chances are the variable was lost before it hits smpwservices.fcc during redirect.
Hongxu