Maven cannot pull jars in snap builds

[Evan]

I'm trying to build a snap of Jenkins (https://code.launchpad.net/~ev/jenkins-snap/master) but it's failing when Maven tries to pull the jars (`mvn dependency:resolve`) in snapcraft pull:

[DEBUG] Using connector BasicRepositoryConnector with priority 0.0 for http://repo.jenkins-ci.org/public/ via snap-proxy.launchpad.net:3128
…
[FATAL] Non-resolvable parent POM for org.jenkins-ci.main:pom:2.8: Could not transfer artifact org.jenkins-ci:jenkins:pom:1.36 from/to repo.jenkins-ci.org (http://repo.jenkins-ci.org/public/): Not authorized by proxy , ReasonPhrase:Proxy Authentication Required. and 'parent.relativePath' points at wrong local POM @ line 28, column 11

The full logs are here:
https://launchpadlibrarian.net/270062518/buildlog_snap_ubuntu_xenial_amd64_jenkins_BUILDING.txt.gz

I don't think this is snapcraft's fault. I tried fetching a jar using urllib inside snapcraft pull, which worked fine.

I asked foli to pull any 417 errors from the proxy logs:
https://pastebin.canonical.com/160015/

[Evan (ev)]

https://dogfood.launchpadlibrarian.net/245146938/buildlog_snap_ubuntu_xenial_amd64_jenkins_BUILDING.txt.gz is a reproduction of this on dogfood

[Colin Watson (cjwatson)]

This is in fact a snapcraft bug: its maven plugin is not handling the authenticated proxy case correctly. It's really not relevant whether urllib works when the maven plugin is explicitly decomposing the proxy URL and turning it into a maven configuration file.

[Colin Watson (cjwatson)]

https://github.com/snapcore/snapcraft/pull/642