Unexpected interaction between GITHUB_PAT and CRAN-like repo

[copernican]

An Artifactory repo can be used to host internally developed R packages. Packages can be installed with a command like

install.packages("foo", repos = "https://our.repo/"

To install a specific version of foo from this repo, I tried

install_version("foo", "x.y.z")

but this fails with a 401 error. This seems to be related to whether GITHUB_PAT is set. I've edited the below reprex to sanitize the internal repo and package details.

remotes::install_version("foo", "x.y.z", upgrade = "never")
#> Downloading package from url: https://our.repo/src/contrib/foo_x.y.z.tar.gz
#> Error: Failed to install 'unknown package' from URL:
#>   HTTP error 401.
#>   Bad credentials
#> 
#>   Rate limit remaining: 47/60
#>   Rate limit reset at: 2020-02-28 18:40:55 UTC
#> 
#> 
Sys.unsetenv("GITHUB_PAT")
remotes::install_version("foo", "x.y.z", upgrade = "never")
#> Downloading package from url: https://our.repo/src/contrib/foo_x.y.z.tar.gz
#> Installing package into '/usr/local/lib/R/3.6/site-library'
#> (as 'lib' is unspecified)

I'm using remotes 2.1.1.

^{Created on 2020-02-28 by the reprex package (v0.3.0)}

[jimhester]

This seems like a duplicate of #440