Building `libzmq` with `libsodium` for CURVE Support

To use the CURVE security mechanism in libzmq, you need to install libsodium.

On macOS, you can easily install libsodium using Homebrew:

brew install libsodium

Alternatively, you can download and build `libsodium` from source.

Building libzmq with CURVE Support

To build libzmq with libsodium and CURVE support, follow these steps:
1. download libzmq source from web site
2. compile and link with 2 flags
3. Install.
4. Uninstall hombrew version 

mkdir build
cd build
cmake -DWITH_LIBSODIUM=ON -DENABLE_CURVE=ON ..
make

After building, the libzmq library will be located in the build/lib directory.

sudo make install

Integrating `libsodium` and CURVE with `libzmq` in Your Project

To link `libsodium` for CURVE support in your project, you can use the following CMake commands:

This is a sample part of a CMakeLists.txt file. In this case, the project requires libzmq wrapped by cppzmq and libsodium.

find_package(PkgConfig REQUIRED)

# Function to find and configure PkgConfig modules
function(find_pkg_config package)
    string(TOUPPER ${package} PACKAGE_NAME)
    pkg_check_modules(${PACKAGE_NAME} REQUIRED ${package})
    include_directories(${${PACKAGE_NAME}_INCLUDE_DIRS})
    link_directories(${${PACKAGE_NAME}_LIBRARY_DIRS})
    set(${package}_LIBS ${${PACKAGE_NAME}_LIBRARIES} PARENT_SCOPE)
endfunction()

# ------------------------------------------------------------------------------
find_pkg_config(cppzmq)
target_link_libraries(${PROJECT_NAME} ${cppzmq_LIBS})

# CURVE requires libsodium.
find_pkg_config(libsodium)
target_link_libraries(${PROJECT_NAME} ${libsodium_LIBS})