[Rd] r-project.org SSL certificate issues

[Gábor Csárdi]

On macOS 10.15.5 and R-devel:

> download.file("https://www.r-project.org", tempfile())
trying URL 'https://www.r-project.org'
Error in download.file("https://www.r-project.org", tempfile()) :
  cannot open URL 'https://www.r-project.org'
In addition: Warning message:
In download.file("https://www.r-project.org", tempfile()) :
  URL 'https://www.r-project.org': status was 'SSL peer certificate or
SSH remote key was not OK'

https://www.ssllabs.com/ssltest says:

COMODO RSA Certification Authority
Fingerprint SHA256:
4f32d5dc00f715250abcc486511e37f501a899deb3bf7ea8adbbd3aef1c412da
Pin SHA256: grX4Ta9HpZx6tSHkmCrvpApTQGo67CYDnvprLg5yRME=
Valid untilSat, 30 May 2020 10:48:38 UTC (expired 8 hours and 51
minutes ago)   EXPIRED

AFAICT this is the reason:
https://calnetweb.berkeley.edu/calnet-technologists/incommon-sectigo-certificate-service/addtrust-external-root-expiration-may-2020

FYI,
Gabor