nilFinx/LiquidProxy ? reverse-engineered prompt

Build me a small Go app that acts as a local proxy for older devices, mainly to help with TLS and SSL problems when connecting to modern mail servers and some HTTP services.

I want it to handle HTTP plus mail protocols like IMAP and SMTP, with support for both STARTTLS and direct TLS where it makes sense. It should include a simple web page for getting the certificate, basic authentication, and a few config flags for things like blocking very modern clients or blocking ancient ones if needed. If some parts are not fully implemented yet, keep the code clean and leave clear placeholders.

Make it easy to build and run from the command line, with a simple Makefile or build script, and split the code into sensible files so it is maintainable. If you need to check current docs or examples for Go proxy handling, look them up online.