go-mitmproxy is a Golang implementation of mitmproxy that supports man-in-the-middle attacks and parsing, monitoring, and tampering with HTTP/HTTPS traffic. Parses HTTP/HTTPS traffic and displays traffic details via a web interface. Supports a plugin mechanism for easily extending functionality. Various event hooks can be found in the examples directory. HTTPS certificate handling is compatible with mitmproxy and stored in the ~/.mitmproxy folder. If the root certificate is already trusted from the previous use of mitmproxy, go-mitmproxy can use it directly. Map Remote and Map Local support.
Powerful, enterprise-ready, open source web server w/ automatic HTTPS
...Though used mostly as an HTTPS server, Caddy can be used to run Go applications, offering automated documentation, graceful on-line config changes via API and more to these apps.
Caddy is very extensible, with a powerful plugin system unlike any other web server.