Blacklist unsafe ports

[cpsievert]

Similar to https://github.com/rstudio/shiny/commit/4fa2af72cc74bf72dc807e1d1709b13711a8a635

Perhaps, this could be handled on the fiery-level, @thomasp85?

[thomasp85]

Hmm... I’d rather not block something in fiery unless there is absolutely no reason to use them in an http server. Fiery is for more than serving sites to browsers. I’ll think about this and read up a bit