I would like to develop an application using the web3j. However, it needs to be just one wallet that multiple users will deposit and withdraw from. The allowances are kept in a centralized database. My concern is safety of this approach, since the private key must be kept safe and used only by the wallet application.
I am thinking about creating a separate micro-service and put the read-only restriction to an encrypted file containing the key, while allowing only a certain application to communicate with the wallet.
What do you think would be the best approach ? Please note that I must use the single wallet and a single secret-key.