Book: Hexagonal Architecture in Go Also by me: Thinking in Go (2-book series) — Complete Guide to Go Programming + Hexagonal Architecture in Go My project: Hermes IDE | GitHub — an IDE for developers who ship with Claude Code and other AI coding tools Me: xgabriel.com | GitHub You've seen this codebase. Every outbound call is wrapped in three lines that add the auth header. Five for logging. Eight for retrying 5xx. Each call site does it slightly differently, so half forget the trace header and a third double-log on retries. The one in internal/jobs/ puts the auth header in the URL. The fix is older than most of the code that needs it. Go's http.RoundTripper interface was put in the standard library exactly so cross-cutting HTTP concerns live in one place (at the boundary between your code and the wire) instead of being smeared across every call site. What http.RoundTripper actually is The interface is one method. type RoundTripper interface { RoundTrip ( * http . Request ) ( * http .…