What is vegur appearing in HTTP headers?
Solution 1:
It's a Heroku proxy/load-balancer adding the Via header.
See: Vegur at GitHub.
Heroku's proxy library based on a forked Cowboy frontend (Cowboyku). This library handles proxying in Heroku's routing stack.
Solution 2:
The via header shows proxies and their names. In this case, the client went through a proxy called "vegur" - either its software or the computer name.