[Support Guide] Using private NPM modules on Netlify

I’m realizing now that the build is not even getting to the user build script – it’s failing when installing yarn:

10:14:17 AM: Build ready to start
10:14:20 AM: build-image version: 9e0f207a27642d0115b1ca97cd5e8cebbe492f63
10:14:20 AM: build-image tag: v3.3.2
10:14:20 AM: buildbot version: 75cd99f62ada9e21edea53208e8baf0eab85a045
10:14:20 AM: Fetching cached dependencies
10:14:21 AM: Starting to download cache of 255.1KB
10:14:21 AM: Finished downloading cache in 104.993978ms
10:14:21 AM: Starting to extract cache
10:14:21 AM: Failed to fetch cache, continuing with build
10:14:21 AM: Starting to prepare the repo for build
10:14:21 AM: No cached dependencies found. Cloning fresh repo
10:14:21 AM: git clone git@gitlab.com:[username]/[repo]
10:14:23 AM: Preparing Git Reference refs/heads/master
10:14:24 AM: Starting build script
10:14:24 AM: Installing dependencies
10:14:26 AM: Downloading and installing node v8.16.0...
10:14:26 AM: Downloading https://nodejs.org/dist/v8.16.0/node-v8.16.0-linux-x64.tar.xz...
10:14:26 AM: 
#
10:14:26 AM:   1.7%
10:14:26 AM: 
#####################
10:14:26 AM:  29.9%
10:14:26 AM: 
################
10:14:26 AM: #################################################         91.0%
10:14:26 AM: 
########################################################################
10:14:26 AM: 100.0%
10:14:27 AM: Computing checksum with sha256sum
10:14:27 AM: Checksums matched!
10:14:29 AM: Now using node v8.16.0 (npm v6.4.1)
10:14:29 AM: Attempting ruby version 2.3.6, read from environment
10:14:30 AM: 
10:14:30 AM: ** WARNING **
10:14:30 AM: Using custom ruby version 2.3.6, this will slow down the build.
10:14:30 AM: To ensure fast builds, set the RUBY_VERSION environment variable, or .ruby-version file, to an included ruby version.
10:14:30 AM: Included versions: 2.6.2
10:14:30 AM: 
10:14:30 AM: Required ruby-2.3.6 is not installed - installing.
10:14:31 AM: Searching for binary rubies, this might take some time.
10:14:31 AM: Found remote file https://rvm_io.global.ssl.fastly.net/binaries/ubuntu/16.04/x86_64/ruby-2.3.6.tar.bz2
10:14:31 AM: Checking requirements for ubuntu.
10:14:32 AM: Requirements installation successful.
10:14:32 AM: ruby-2.3.6 - #configure
10:14:32 AM: ruby-2.3.6 - #download
10:14:33 AM: ruby-2.3.6 - #validate archive
10:14:41 AM: ruby-2.3.6 - #extract
10:14:45 AM: ruby-2.3.6 - #validate binary
10:14:46 AM: ruby-2.3.6 - #setup
10:14:47 AM: ruby-2.3.6 - #gemset created /opt/buildhome/.rvm/gems/ruby-2.3.6@global
10:14:47 AM: ruby-2.3.6 - #importing gemset /opt/buildhome/.rvm/gemsets/global.gems
10:14:49 AM: ............................................................
10:14:49 AM: ruby-2.3.6 - #generating global wrappers
10:14:49 AM: .......
10:14:49 AM: ruby-2.3.6 - #gemset created /opt/buildhome/.rvm/gems/ruby-2.3.6
10:14:49 AM: ruby-2.3.6 - #importing gemsetfile /opt/buildhome/.rvm/gemsets/default.gems evaluated to empty gem list
10:14:49 AM: ruby-2.3.6 - #generating default wrappers
10:14:49 AM: .......
10:14:50 AM: Using /opt/buildhome/.rvm/gems/ruby-2.3.6
10:14:50 AM: Using ruby version 2.3.6
10:14:50 AM: Using PHP version 5.6
10:14:50 AM: Started restoring cached node modules
10:14:50 AM: Finished restoring cached node modules
10:14:50 AM: Started restoring cached yarn cache
10:14:50 AM: Finished restoring cached yarn cache
10:14:50 AM: Installing yarn at version 1.3.2
10:14:50 AM: Installing Yarn!
10:14:50 AM: > Downloading tarball...
10:14:50 AM: [1/2]: https://yarnpkg.com/downloads/1.3.2/yar
10:14:50 AM: n-v1.3.2.tar.gz --> /tmp/yarn.tar.gz.3XCWlG4Gdu
10:14:50 AM:   % Total    % Received % Xferd  Average
10:14:50 AM: Speed   Time    Time     Time  Current
10:14:50 AM:                       Dload  Upload   T
10:14:50 AM: otal   Spent    Left  Speed
10:14:50 AM: 
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:-
10:14:50 AM: -:--     0
10:14:51 AM: 
100    91  100    91    0     0    320      0 --:--:-- --:--:-- --:--:--
10:14:51 AM: 321
10:14:51 AM: 
100   608    0   608    0     0    955
10:14:51 AM:   0 --:--:-- --:--:-- --:--:--   955
10:14:51 AM: 
  0  865k    0     0    0     0      0      0 --:--:-- --:
10:14:51 AM: --:-- --:--:--     0
10:14:51 AM: 
100  865k  100  865k    0     0   796k      0  0:00:01  0:00:01
10:14:51 AM: --:--:-- 5549k
10:14:51 AM: [2/2]: https://yarnpkg
10:14:51 AM: .com/downloads/1.3.2/yarn-v1.3.2.tar.gz.asc --> /tmp/yarn.tar.gz.3XCWlG4Gdu.asc
10:14:51 AM: 
100    95  100    95    0     0   2247      0 --:--:-- --:--
10:14:51 AM: :-- --:--:--  2247
10:14:52 AM: 
100   612    0   612    0     0   3991      0 --:--:-- --:--:
10:14:52 AM: -- --:--:--  3991
10:14:52 AM: 
100  1027  100  1027    0     0   5327      0 --:--:-- --:
10:14:52 AM: --:-- --:--:--  5327
10:14:52 AM: > Verifying integrity...
10:14:52 AM: gpg: Signature made Thu 02 Nov 2017 04:44:10 PM UTC using RSA key ID FD2497F5
10:14:52 AM: gpg: Good signature from "Yarn Packaging <yarn@dan.cx>"
10:14:52 AM: gpg: Note: This key has expired!
10:14:52 AM: Primary key fingerprint: 72EC F46A 56B4 AD39 C907  BBB7 1646 B01B 86E5 0310
10:14:52 AM:      Subkey fingerprint: 6A01 0C51 6600 6599 AA17  F081 46C2 130D
10:14:52 AM:  FD24 97F5
10:14:52 AM: > GPG signature looks good
10:14:52 AM: > Extracting to ~/.yarn...
10:14:52 AM: > Adding to $PATH...
10:14:52 AM: > We've added the following to your /opt/buildhome/.profile
10:14:52 AM: > If this isn't the profile of your current shell then please add the following to your correct profile:
10:14:52 AM: export PATH="$HOME/.yarn/bin:$HOME/.config/yarn/global/node_modules/.bin:$PATH"
10:14:52 AM: 
10:14:52 AM: > Successfully installed Yarn 1.3.2! Please open another terminal where the `yarn` command will now be available.
10:14:53 AM: Installing NPM modules using Yarn version 1.3.2
10:14:53 AM: yarn install v1.3.2
10:14:54 AM: [1/4] Resolving packages...
10:14:54 AM: [2/4] Fetching packages...
10:14:56 AM: error An unexpected error occurred: "https://node.bit.dev/ajsharp.vinvin.booking-time-field/-/ajsharp.vinvin.booking-time-field-1.0.0.tgz: Request failed \"401 Unauthorized\"".
10:14:56 AM: info If you think this is a bug, please open a bug report with the information provided in "/opt/build/repo/booking-plugin/yarn-error.log".
10:14:56 AM: info Visit https://yarnpkg.com/en/docs/cli/install for documentation about this command.
10:15:07 AM: Error during Yarn install
10:15:07 AM: failed during stage 'building site': Build script returned non-zero exit code: 1
10:15:07 AM: Error running command: Build script returned non-zero exit code: 1
10:15:08 AM: Shutting down logging, 2 messages pending