[R-SIG-Mac] Installing openssl package in R-devel

[Duncan Murdoch]

I'm trying to install the openssl package on an M3 Mac in R-devel.  It 
keeps failing with these messages:

> * installing *source* package ‘openssl’ ...
> ** package ‘openssl’ successfully unpacked and MD5 sums checked
> ** using staged installation
> Homebrew >=4.1.0 (shallow or no git repository)
> Using PKG_CFLAGS=-I/usr/local/opt/openssl/include
> --------------------------- [ANTICONF] --------------------------------
> Configuration failed because openssl was not found. Try installing:
>  * deb: libssl-dev (Debian, Ubuntu, etc)
>  * rpm: openssl-devel (Fedora, CentOS, RHEL)
>  * csw: libssl_dev (Solaris)
>  * brew: openssl (Mac OSX)
> If openssl is already installed, check that 'pkg-config' is in your
> PATH and PKG_CONFIG_PATH contains a openssl.pc file. If pkg-config
> is unavailable you can set INCLUDE_DIR and LIB_DIR manually via:
> R CMD INSTALL --configure-vars='INCLUDE_DIR=... LIB_DIR=...'

I did install the openssl lib using Simon's install.libs() function from 
https://mac.r-project.org/bin/, and I do have pkg-config installed in 
/opt/R/arm64/bin and I see this:

$ pkg-config openssl --cflags
-I/opt/R/arm64/include

So I don't know where the openssl config is finding the Homebrew info. 
Can someone suggest what I need to do to get this to work?

Duncan Murdoch