Difficulty compiling Apache with --enable-ssl

While trying to configure Apache to serve https with a newly installed certificate from certbot, I learned that mod_ssl isn't enabled. It's not even in the modules directory. I tried recompiling Apache with the --enable-ssl option and saw no change in the ability to use the definitions from mod_ssl. What else can I do to get mod_ssl enabled in my apache config?

I got this error when configuring:

./configure --with-included-apr --with-included-apr-util --enable-ssl --prefix=/usr/local/httpd

checking whether to enable mod_ssl... 
checking dependencies checking for OpenSSL... 
checking for user-provided OpenSSL base directory... none 
checking for OpenSSL version >= 0.9.8a... FAILED 
configure: WARNING: OpenSSL version is too old no checking whether to enable mod_ssl... 
configure: error: mod_ssl has been requested but can not be built due to prerequisite failures

I tried installing openssl and was told I was already at the highest version:

%>apt-get install openssl
Reading package lists... Done
Building dependency tree       
Reading state information... Done
openssl is already the newest version (1.1.0l-1~deb9u1).

Some have asked about OS:

Linux toesr-instance 4.9.0-11-amd64 #1 SMP Debian 4.9.189-3+deb9u2 (2019-11-11) x86_64 GNU/Linux

After some other searching, it appears that libssl-dev was also required. Installing that and then running configure resolved the issue.