NCSA httpd introduced the Common Gateway Interface which allows you to execute any binary, and whatever it puts on stdout is sent as the reply. Back then it was typically a Perl script or a compiled C binary.
My company makes a DAS(distributed Antenna System) product with an embedded web interface. All of our web sites have C/C++ cgi back ends. There are more makefiles in the Web folder than the whole rest of system. It is quite mind boggling. But the engineer that has control over this area is stuck in the 90s.
https://en.m.wikipedia.org/wiki/Common_Gateway_Interface