ExternalProject_Add -> vcpkg or Conan. I have more experience with vcpkg and the steps are:

1) declare your dependencies in a vcpkg.json file (similar to npm's package.json). Example:

{ ... "dependencies": [ "openssl" ] }

2) Add it to your CMakeLists.txt file. Example:

    find_package(OpenSSL REQUIRED)
    target_link_libraries(main PRIVATE OpenSSL::SSL OpenSSL::Crypto)