The Forge CLI does make requests to an Atlassian server, and does attempt to store your own API key on your computer. If your company enforces restrictions that do not allow these functions, the Forge CLI may not be able to work correctly.
For the requests to the server, you can set a proxy by using the shell environment variable
FORGE_GRAPHQL_GATEWAY, which defaults to
https://api.atlassian.com/graphql within the CLI. If you require, you may be able to set up a proxy which passes the requests through the proxy to the default URL.
Currently, the CLI is indeed a closed source project. Are there particular reasons you would like to see it open sourced? It would be helpful for us to know this, so we are able to appropriately prioritise making that happen.