How to do a server to server response to a POST

user_4533742 0
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I am working on an old classic asp site that uses vbscript for the server code and HTML and JavaScript for the client end. I am communicating with an external server which handles the credit card payment details.

I have found loads of answers for getting the response from a POST to the server (both from the client using JavaScript and from our own website server using vbscript). However what I am failing to find is how to respond from my server to an POST made from the credit card gateway server.

The sequence goes something like this:

  1. I post all the transaction details to the gateway server
  2. They immediately respond with a success status, a security key, a transaction ID, and a URL to which I must immediately redirect.
  3. They then send a 'notification' post to a URL, that I gave in the first post, with an MD5 hash made up from details of the transaction and, importantly, the security key. I must generate the same MD5 hash and check that it matches. This is obviously to confirm that the initial transaction has not been compromised in any way.
  4. Having done the security check I am required to respond: "When we receive your response to our notification POST, we determine where to direct your customers browser based on your response Status:"

That last stage is the one I am struggling with. I'm sure it's something really simple and silly but I just can't find any information anywhere. I have found lots of stuff on HTTPResponse but that all seems to be getting the response from a POST that I have made (and I have used this in the earlier stages) whilst here I am wanting to generate a response to a POST I have received. Note this must all be done at my server end as the credit card gateway have the IP address of our server and will only accept these transactions from that IP address therefore none of this can be sent from the customer's browser.

Sorry if this is really dumb! I am a C++ developer not a web developer but, as is the way with these things, I am having to do this bit of web development!

asp-classic response post vbscript
1 Answers

What you are talking about here is a consumer (the Gateway server) sending a POST request to an endpoint on your web application, which you should handle just the same as if you were receiving a POST from a local request, the process is the same.

Here is a basic example;

<%
'Expect only POST data to this page
If UCase(Request.ServerVariables("REQUEST_METHOD") & "") = "POST" Then
  'Craft your response
  Call BuildResponse()
Else
  'Anything other then a POST should be met with a 404 response.
  Response.Status = "404 Not found"
End If
Call Response.End()

'Sub for crafting your response.
Sub BuildResponse()
  'Do we have a form field of "somevalue" with a value of "yes"?
  If LCase(Request.Form("somevalue") & "") = "yes" Then
    Call Response.Write("Hello world - Valid")
  Else
    Call Response.Write("Hello world - Invalid")
  End If
End Sub
%>

This is just a basic example that expects a form post parameter of "somevalue" with a value of "yes". Based on this it returns a conditional response. Obviously, you will need to pad out the response based on your requirements but this should give you some idea of how to structure it.

Side-note: As you won't be the consumer yourself it might be an idea to output a text file or setup an email that reports the passed form parameters to help you debug what the consumer is POSTing to the page to help you work out how to handle the request and generate a valid response the consumer expects.

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