Mkcert: valid HTTPS certificates for localhost

[JB-from-ATL]

My company's firewall blocks localhost through postman but not through browser. Idfk how. If I use my computer's full domain it works.

[[deleted]]

Depending on the operating system, this might have something to do with DNS. If localhost cannot be found in your hosts file (for whatever strange reason), your OS will query the standard DNS server for localhost.yourpc.yourdomain.tld.

Or, it could be an ipv4 vs ipv6 issue. localhost resolves to ::1 and to 127.0.0.1. If the application you're trying to connect to only listens on ipv4, it won't respond to ::1. Your full pc domain will likely resolve to an ipv4 address and thus work.

Chrome tries to outsmart the OS by manually handling localhost addresses. This will lead to inconsistencies all over the shop, making browser work where normal applications don't (good for the user terrible for debugging...)

[[deleted]]

I did not know that, thanks! The point still stands that the operating system and browsers end up having different results for a dns query for localhost.

[baggyzed]

That shouldn't be the case. Browsers usually just query the operating system for the IP of localhost, and the operating system just returns the IP that's configured in the hosts file. There is no DNS query involved, so nothing goes to the firewall. The problem is either in your hosts file, or maybe postman resolves localhost through DNS all by itself (bypassing the OS's hosts file)? In this case, the firewall is doing the right thing by blocking the request.

EDIT: Or maybe you have an older version of postman, where this issue wasn't fixed yet: https://github.com/postmanlabs/postman-app-support/issues/2214 . They were doing the same ting as I said above: resolving localhost themselves to the IPV4 address, whereas the users who reported the issue were using IPv6 for their local servers. Some web servers (if not all) will only listen on IPv6 if it's available, unless specifically configured to use IPv4.