Having trouble logging in via the API

[excelhero]

I am trying to login using the login_login api, but keep getting invalid signature (this specifically: {"response":{"errormessage":["invalid_api_signature","Invalid API Signature"]}})

Below is the pattern I am following. Init works fine and returns various values that I then use in the Login method. For reference, the code is Classic ASP. What am I missing here?

vBulletinApiURL = "http://www.myurl.com/campus/api.php"
vBulletinUid = "myuid"
vBulletinPwd = "mypwd"
vBulletinApiKey = "xgZb1tyk"
vBulletinGUID = "99d50807-c642-4569-8f41-10ed978eb197"

Init()
Login()

Sub Init()
  dim url
  url = ToFormat("{0}?api_m=api_init&clientname=ham&clientversion=1.0&platformname=android&platformversion=4.0&uniqueid={1}", _ 
      Array(vBulletinApiURL, vBulletinGUID))

  dim objSrvHTTP: Set objSrvHTTP = Server.CreateObject ("Msxml2.ServerXMLHTTP.6.0")		
  objSrvHTTP.open "GET",url, false
  objSrvHTTP.send 

  Dim apiRet: Set apiRet = JSON.parse(objSrvHTTP.responseText)

  strSecret = apiRet.secret
  strAccessToken = apiRet.apiaccesstoken
  strApiClientID = apiRet.apiclientid
  strApiVersion = apiRet.apiversion

  Set objSrvHTTP = nothing

End Sub

Sub Login()
  dim objSrvHTTP: Set objSrvHTTP = Server.CreateObject ("Msxml2.ServerXMLHTTP.6.0")
    
  ' the keys must be in sorted order
  dim strLoginString: strLoginString = ToFormat("api_m=login_login&vb_login_md5password={1}&vb_login_username={0}", _ 
              Array(vBulletinUid, MD5(vBulletinPwd)))

  ' convert everything with URLEncode (just in case)
  strAccessToken= Server.URLEncode(strAccessToken)
  strApiClientID= Server.URLEncode(strApiClientID)
  strSecret= Server.URLEncode(strSecret)		
  strApiVersion= Server.URLEncode(strApiVersion)

  dim strSignature: strSignature = strLoginString & strAccessToken & strApiClientID & strSecret& vBulletinApiKey
  strSignature = Server.URLEncode(MD5(strSignature))

  dim strApiRegInfo: strApiRegInfo = ToFormat("api_c={0}&api_s={1}&api_sig={2}&api_v={3}", _ 
    Array(strApiClientID, strAccessToken, strSignature , strApiVersion))

  dim strLoginRequest: strLoginRequest = ToFormat("{0}&vb_login_username={1}&vb_login_md5password={2}", _
    Array(strApiRegInfo, vBulletinUid, MD5(vBulletinPwd)))

  dim strUrl: strUrl = vBulletinApiURL & "?api_m=login_login"

  objSrvHTTP.open "POST", strUrl, false
  objSrvHTTP.setRequestHeader "Content-Type", "application/x-www-form-urlencoded"
  objSrvHTTP.send strLoginRequest

  Response.Write("ret text: " & objSrvHTTP.responseText & "<br/>") 

End Sub