[R] broken installation on ubuntu 16.04 for 3.4.4-1xenial0

[KZ Win]

We have a test  system for boostrapping a production machine running R
code.  It spins up a new machine and tries to install this version whenever
there is a new commit to our infrastructure code repo.  This version has
been in place since Mar 2018 but a few weeks ago this test fails because it
can no longer install this package even though we have not made any changes
to this installation process.

The failure comes with this message

```
WARNING: The following packages cannot be authenticated!
r-base-core r-cran-boot r-cran-cluster r-cran-foreign r-cran-mass
r-cran-kernsmooth r-cran-lattice r-cran-nlme r-cran-matrix r-cran-mgcv
r-cran-rpart r-cran-survival r-cran-class r-cran-nnet r-cran-spatial
r-cran-codetools r-recommended r-base r-base-dev r-base-html r-doc-html
STDERR: E: There were unauthenticated packages and -y was used without
--allow-unauthenticated```

Any idea on whether there is a way to install `r-base` without using
`--allow-unauthenticated`

I can provide more information if necessary.

Thank you

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