Is there a simple LDAP-to-HTTP gateway out there?

Taking Andrew's suggestion and turning this into an answer...

The consensus seems to be that there isn't a pre-existing solution out there and that I should just get off my lazy derriere and write one. So I did, and it's available from:

• http://githup.com/larsks/ldap2json

It's not especially pretty, but it works for my prototyping and I figure maybe someone else will find it useful someday. The code does not currently handle authentication. If you're lucky, it might handle a server disconnect. It does support JSONP, which is what I needed in order to integrate this with our third-party hosted service.

I did find one product out there that claims to do the same thing, but it's a commercial product and I don't know anything about the pricing.

This is an old question, however for anyone else looking for solutions in this space I've stumbled across Json2Ldap which exposes a LDAP server with a JSON-RPC protocol.

This provides you with the ability to build some pretty targeted queries and keep things nice and efficient. Also supports everything you would expect in terms of auth, tokens for different endpoints and controlling what type of level of abuse you'd like to open up your directly to by outside hands.