In a project I'm working on at the minute, using PHP, I need some way for a PHP script on one server to notify a PHP script on a completely different server that it needs to update its database. The first script will have to pass some information into the second script and possibly get an error code back. All communication should be done over HTTP.

My first solution was a method that involved security by obscurity - that is, just running a script that noone knows about, but it would of course be fairly simple to find out about it and send in malicious data.

So, I'd like some suggestions of how to do this with minimal possibility for exploiting by malicious individuals.

Any ideas would be very much appreciated.

TIA,
- QS Computing.

Here are a few thoughts that go beyond the log in as user on the second system.

Since you know which machine the request is coming from you could use the IP address as part of your security solution. Essentially only allow the second script to run if the request comes from a particular IP address.

Establish a password exchange as follows:
server 1 says hello
server 2 says give me the encrypted password with the following salt
server 1 receives the salt and so encrypts the password something like: md5(password.salt)
server 2 checks the encrypted value and accepts the transaction - or not!

Rather than get the first server to send the information, get the second server to take it from the first server. That way it makes it harder for a third part to provide malicious data.

graeme.

I think the method of taking it from the second server sounds best. So, if I get the first server to poll the second server, and then it runs a script to take the data back from the first server, that should eliminate the security issues somewhat. It's not really an issue if the data is seen; it's fairly public data anyway.

You will need to keep track of the files but that is quite simple.

It may work as follows:

server 1 tells server 2 the data is ready
server 2 runs the script and gets the data from server 1 and thus updates the database

Now someone finds this script and wonders what does it do, and so runs it.

server 2 runs the script and gets the data from server 1, but realises that it has already run this data file and so ignores it.

(The data file could have a timestamp header, requiring server 1 to send the name of the file will help but you don't want anyone getting lucky!)

If the 2nd server has SSL, just use curl and send the password w/ the request. SSL will ensure no one sees the password.