Deployment strategy for servers on internal network I am following composer based workflow for Drupal 8, in which I commit only custom code and use composer install to install it on another environment.

However, on new workflow, the dev, test, staging instances are on Internal network, with no access to Internet (due to security reasons).

Can you suggest a deployment strategy to use in this scenario, so that I don't have to commit the whole files in git repository, as is.

PS: I am ok with something like Acquia pipelines, where things are 'compiled' into a branch, which is used for deployment. But using that is ruled out, as the code can't be sent to outside because of security concerns.
The correct way is to use Acquia BLT. It generates a deployment artifact, which can be deployed anywhere.

So that the composer will stay in local and the deployment artifact can be committed to a different branch for deployment, with all the dependencies.