HTML form authentication using BIGIP local database

Hi

I would like to use a HTML form to do authentication and compare the username and password to a data group in the BIGIP but it seems that when i enter the username or password, it is not retrieve and compare to the value in the data group. The idea is when type the URL, it will redirect to the login HTML form page then the value inserted should be retrieve but it is not working. Any idea why it is not working from the code? i am thinking that probably because the POST from the HTML form have no action to be performed. I have reference to some other article regarding this and this is what i got so far. The HTML form is just a HTTP::respond giving the HTML form when a certain URL is type in.

when HTTP_REQUEST_DATA {


  set namevals [split [HTTP::payload] "&"]
  set [HTTP::username] username   
  set [HTTP::password] password    
  set auth_id  1
   Break out the POST data for username and password values
 for {set i 0} {$i < [llength $namevals]} {incr i} {
    set params [split [lindex $namevals $i] "="]
    if { [lindex $params 0] equals "username" } {
      set auth_username [lindex $params 1]
    }
    if { [lindex $params 0] equals "password" } {
      set auth_password [lindex $params 1]
    }
  }
  AUTH::username_credential $auth_id $username
  AUTH::password_credential $auth_id $password
  AUTH::authenticate $auth_id
  HTTP::collect



if { [HTTP::username] eq "" or [HTTP::password] eq "" } {
     Grab username and password from authorization header and compare
    if { $username || $password } { 
        HTTP::respond 200 content  "No username and password in Authorization header or Auth header missing." 
        } 
 Next look in the datagroup called LocalUsers for the user. The value is a hex    D5password.Compare the value in the datagroup to the value of HTTP::password to determine if this is valid.
        set password [class lookup "$username" test_local_user] 
        if { $password eq "" } {
            if { $auth_id ==1 } { HTTP::respond 200 content  "Auth failed for user [HTTP::username] \ and the value in the datagroup was [class lookup [HTTP::username] LocalUsers] "} 
        } else {
           Convert password to MD5 hash in hex
            binary scan [ md5 [$password]] H* hexhash 
            if { $password } { log local0. "password MD5 = $hexhash" } 
            if { $password eq $hexhash } { 
                pool test_pool
                if { $auth_id } { HTTP::respond 200 content "Auth succeeded for user [HTTP::username] and the value in the datagroup was [class lookup [HTTP::username] LocalUsers] "}
                 Exit this event for this iRule to prevent sending a 401 below
                return 
            } 
        } 
    }
HTTP::respond 401 content "Error:Authentication Failure" WWW-Authenticate "Basic realm=\"local.loc\""
}