I have a requirement to validate a data field (a reference number for payments) in our finance system by connecting to one of our vendor's API services. The finance system does not have the connectivity to internet but can connect to the local network and the other servers, that have the connectivity to internet\cloud services. Could you please provide some advise on what solution options are available for me to satisfy this requirement?
You can either create a proxy on one of the servers that has access to the internet or create an api and host it on one of those servers.
In case of the proxy you route the request to the vendors api throug the proxy (basically giving it internet access), the proxy will execute the call to the vendors api and return the result to the finance system.
The other option is to create a small service which is build to call the vendors api. The service will be hosted on one of the servers that has internet access. It then exposes an api itself which you can call from the finance system. It basically acts as a proxy but without exposing the whole internet to the finance system. Make sure that the api is only available to the internal network to minimize security risks.