I am trying to do the following:

• Have a daemon running on a server
• That daemon exposes an API (Json, etc...)
• I can call that API from localhost with: 1: Address From 2: Address To 3: Key for Address From
• The daemon creates a valid transaction using the unspent outputs, signs the transaction using the key, and broadcasts it to the network, then forgets about the key.

I don't want the daemon to store the private key (stateless) and sign transactions on-demand. The daemon should be as light as possible (if possible, use less than 256 MB of RAM).

I looked at Bitcoind but it doesn't seem to provide that kind of API, since I either need to setup the wallet with the private key beforehand (not stateless) or build the raw transaction from scratch, and I don't want to have to figure out the outputs to use, format of the raw transaction, etc...

What's the easiest way to achieve this?