R install.packages() fails: 'Peer certificate cannot be authenticated with given CA certificates'

[myglc2]

With GuixSD user config ...

(use-package-modules
 base   ; glibc-utf8-locales
 ssh    ; mosh
 admin  ; tree
 aspell ; aspell-dict-en
 mail   ; notmuch mu isync
 statistics ; r
 emacs      ; emacs-ess
 certs      ; nss-certs
 )
(packages->manifest
 (list
  mosh
  tree
  aspell-dict-en ; because emacs doesn't find system install
  notmuch mu isync ; also building from git source but this gets run-time 
dependencies
  r emacs-ess
  r-devtools r-openssl r-stringr r-xml2 r-httr 
  )
 )

... if I try to install a CRAN package like this ...

install.packages("pROC")

... it fails like this ...

Warning: unable to access index for repository 
https://rweb.crmda.ku.edu/cran/src/contrib:
  cannot download all files
Warning messages:
1: In download.file(url, destfile = f, quiet = TRUE) :
  URL 'https://cran.r-project.org/CRAN_mirrors.csv': status was 'Peer 
certificate cannot be authenticated with given CA certificates'
2: package ‘pROC’ is not available (for R version 3.3.1) 

But if I "defeat" HTTPS like this ...

options(repos=
            c(
                CRAN = "http://cran.rstudio.com/";
            )
        )

... it works. I would prefer to use HTTPS, so here is the question:

How do I get R to present the CA certificates?

TIA - George

Full R session log is shown below.

***
R version 3.3.1 (2016-06-21) -- "Bug in Your Hair"
Copyright (C) 2016 The R Foundation for Statistical Computing
Platform: x86_64-unknown-linux-gnu (64-bit)

R is free software and comes with ABSOLUTELY NO WARRANTY.
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Type 'license()' or 'licence()' for distribution details.

  Natural language support but running in an English locale

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Type 'contributors()' for more information and
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Type 'q()' to quit R.

> options(STERM='iESS', str.dendrogram.last="'", editor='emacsclient', 
> show.error.locations=TRUE)
> sessionInfo()
R version 3.3.1 (2016-06-21)
Platform: x86_64-unknown-linux-gnu (64-bit)

locale:
 [1] LC_CTYPE=en_US.utf8       LC_NUMERIC=C             
 [3] LC_TIME=en_US.utf8        LC_COLLATE=en_US.utf8    
 [5] LC_MONETARY=en_US.utf8    LC_MESSAGES=en_US.utf8   
 [7] LC_PAPER=en_US.utf8       LC_NAME=C                
 [9] LC_ADDRESS=C              LC_TELEPHONE=C           
[11] LC_MEASUREMENT=en_US.utf8 LC_IDENTIFICATION=C      

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     
> install.packages("pROC")
Installing package into ‘/home/g1/R/x86_64-unknown-linux-gnu-library/3.3’
(as ‘lib’ is unspecified)
--- Please select a CRAN mirror for use in this session ---
Warning: failed to download mirrors file (cannot download all files); using 
local file 
'/gnu/store/7543j3zkn95i7ixlc9fdq9hj0zrk5yq8-r-3.3.1/lib/R/doc/CRAN_mirrors.csv'
HTTPS CRAN mirror 

 1: 0-Cloud [https]                2: Austria [https]             
 3: Belgium (Ghent) [https]        4: Chile [https]               
 5: China (Beijing 4) [https]      6: Colombia (Cali) [https]     
 7: France (Lyon 1) [https]        8: France (Lyon 2) [https]     
 9: France (Paris 2) [https]      10: Germany (Münster) [https]   
11: Iceland [https]               12: Italy (Padua) [https]       
13: Japan (Tokyo) [https]         14: Mexico (Mexico City) [https]
15: New Zealand [https]           16: Russia (Moscow) [https]     
17: Spain (A Coruña) [https]      18: Spain (Madrid) [https]      
19: Switzerland [https]           20: UK (Bristol) [https]        
21: UK (Cambridge) [https]        22: USA (CA 1) [https]          
23: USA (KS) [https]              24: USA (MI 1) [https]          
25: USA (TN) [https]              26: USA (TX) [https]            
27: USA (WA) [https]              28: (HTTP mirrors)              


Selection: 23
Warning: unable to access index for repository 
https://rweb.crmda.ku.edu/cran/src/contrib:
  cannot download all files
Warning messages:
1: In download.file(url, destfile = f, quiet = TRUE) :
  URL 'https://cran.r-project.org/CRAN_mirrors.csv': status was 'Peer 
certificate cannot be authenticated with given CA certificates'
2: package ‘pROC’ is not available (for R version 3.3.1) 
> q("no")

Process R finished at Thu Sep 29 19:07:12 2016
***