I need help making a cgi script that will accept an ebay user name and
password to verifiy if its valid on ebay servers. if yes, then it
allow the userto continue, if not then it will produce an  error
message

I'm not sure that this is even answerable. 

If a cgi programmer would actually post the answer anyone could use
this script for malicious activity.

Why would anyone need this unless they are wanting to steal peoples
accounts. There is no need for this and there is no possible way for
you to make one.

Yeah you could set up a program to verify the name but you can also
check there website and put in a user name and hit search. Obtaining
the passwords just would not happen.

Ebay allows this through their web services.That is how auction
snipers logon with the ebay user IDs and passwords and auction an
item.
The technical details can be seen under Developers or Affliates links.
see the sample documnt here

http://developer.ebay.com/DevZone/support/KnowledgeBase.asp
and follow this link to pdf document
"Working with eBay Authentication and Auth"
-sen logan

You can write a simple tcp application to do this. Log-in, secure or
insecure, etc. But allowing the user to continue browsing its a little
more hard.

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