At the previous company I worked at, we had a need for something like postman, that could be deployed into specific private networks, for testing, as the only external connections allowed had to be over https, without getting a lot of exceptions by creating tickets to the security team. I created a very lightweight clone of postman that ran in a docker container, so it was easily deployed into a secure environment. The source was pretty tiny. Extremely useful for debugging in the scenarios we had, but sadly I rand out of time trying to open source it before I left the company. I haven't had a need to recreate something similar yet.