Conan install fails with environment variables

Summary

Our documentation states the following, regarding Add your credentials to the GitLab remote for Conan:

Alternatively, you can explicitly include your credentials in any given command. For example:

CONAN_LOGIN_USERNAME=<gitlab_username or deploy_token_username> CONAN_PASSWORD=<personal_access_token or deploy_token> conan upload Hello/0.1@mycompany/beta --all --remote=gitlab

This does not work in the context of installing a package. It only works when uploading.

Steps to reproduce

Run this in a private project on gitlab.com

stages:
  - publish
  - install

variables:
  RECIPE: Hello/0.1@mycompany/beta

conan:publish:
  stage: publish
  image: conanio/gcc8
  script:
    - git clone --depth 1 https://github.com/conan-io/hello
    - cd hello
    - conan new Hello/0.1 -t
    - conan remote add gitlab ${CI_API_V4_URL}/projects/$CI_PROJECT_ID/packages/conan
    - conan create . mycompany/beta
    - CONAN_LOGIN_USERNAME=ci_user CONAN_PASSWORD=${CI_JOB_TOKEN} conan upload ${RECIPE} --all --remote=gitlab

conan:pull-auth-through-env-vars:
  stage: install
  image: conanio/gcc8
  script:
    - conan remote add gitlab ${CI_API_V4_URL}/projects/$CI_PROJECT_ID/packages/conan
    - CONAN_LOGIN_USERNAME=ci_user CONAN_PASSWORD="${CI_JOB_TOKEN}" conan install -r gitlab ${RECIPE}

conan:pull-auth-through-configuration:
  stage: install
  image: conanio/gcc8
  script:
    - conan remote add gitlab ${CI_API_V4_URL}/projects/$CI_PROJECT_ID/packages/conan
    - conan user ci_user -p "${CI_JOB_TOKEN}" -r gitlab
    - conan install -r gitlab ${RECIPE}

Example Project

What is the current bug behavior?

Installing fails: package is not found

What is the expected correct behavior?

Installing succeeds

Relevant logs and/or screenshots

Output of checks

Results of GitLab environment info

Expand for output related to GitLab environment info

(For installations with omnibus-gitlab package run and paste the output of:
`sudo gitlab-rake gitlab:env:info`)

(For installations from source run and paste the output of:
`sudo -u git -H bundle exec rake gitlab:env:info RAILS_ENV=production`)

Results of GitLab application Check

Expand for output related to the GitLab application check

(For installations with omnibus-gitlab package run and paste the output of:
sudo gitlab-rake gitlab:check SANITIZE=true)
(For installations from source run and paste the output of:
sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production SANITIZE=true)
(we will only investigate if the tests are passing)

Possible fixes