From microsoft/vcpkg#6 (comment), Orphis wrote:

In modern CMake, you are not supposed to give the user a list of variables but an imported target you use directly with "target_link_libraries".
It's a bit sad to see the example requiring CMake 3.0 but using patterns from CMake 2.6 dating from the CMake stone age.
https://cmake.org/cmake/help/v3.6/command/add_library.html#imported-libraries

find_library(CPPREST_LIBRARY cpprest_2_8)
find_path(CPPREST_INCLUDE_DIR cpprest/version.h)
include_directories(${CPPREST_INCLUDE_DIR})
link_libraries(${CPPREST_LIBRARY})

You should be providing instead something like "find_package(vcpkg::cpprest_2_8 REQUIRED)" and then have people link against the target "vcpkg::cpprest_2_8".
You can generate files for find_package directly that create the imported targets for you.
The pkg-config CMake support upstream has been doing that.