Accessing include directories of a cmake project added as subdirectory - c++

Question

Consider a simple scenario where my cmake project adds a dependency as a subdirectory:
.
├── CMakeLists.txt
├── src
├── include
│
└── externals
└── BAR
├── CMakeLists.txt
├── src
└── include
The main CMakeLists.txt is something like:
cmake_minimum_required(VERSION 3.0)
project(FOO)
add_subdirectory(externals/BAR)
set(SOURCES ${CMAKE_SOURCE_DIR}/src/foo.cpp
${CMAKE_SOURCE_DIR}/include/bar.hpp)
add_library(${PROJECT_NAME} SHARED ${SOURCES})
target_include_directories(${PROJECT_NAME} PUBLIC
${CMAKE_SOURCE_DIR}/include # this works
${BAR_INCLUDE_DIR}) # this does not
The problem is, the include directories of the added project are not accessable from FOO project.
BAR is a huge dependency with its own sub directories. Its root cmake uses INCLUDE_DIRECTORIES command (instead of target_include_directories). It then does some FILE ( GLOB headers and use them when triggering make install
I am aware that there are many questions regarding subdirectories in cmake, however, in my case cannot modify the CMakeLists.txt in the subdirectory. It's a git submodule that gets updated constantly and it's a pain to modify it constantly.
How can I access BAR's include directories (and later its libraries) without changing its cmakes?
P.S. BAR gets compiled properly and shared library appears in the build folder.