CMake: Enable use of external msquic (#256)

CMakeLists.txt

@@ -83,15 +83,21 @@ else()
     add_subdirectory(ls-qpack)
 endif()
 
-# Configure and build msquic dependency.
-if (WIN32)
-    set(QUIC_TLS "schannel" CACHE STRING "TLS Library to use")
+# msquic dependency
+option(MSH3_USE_EXTERNAL_MSQUIC "Use an external msquic installation")
+if(MSH3_USE_EXTERNAL_MSQUIC)
+    find_package(msquic CONFIG REQUIRED)
 else()
-    set(QUIC_TLS "openssl" CACHE STRING "TLS Library to use")
+    # Configure and build
+    if (WIN32)
+        set(QUIC_TLS "schannel" CACHE STRING "TLS Library to use")
+    else()
+        set(QUIC_TLS "openssl" CACHE STRING "TLS Library to use")
+    endif()
+    set(QUIC_BUILD_SHARED ON CACHE BOOL "Builds MsQuic as a dynamic library")
+    set(QUIC_ENABLE_LOGGING ON CACHE BOOL "Enable MsQuic logging")
+    add_subdirectory(msquic)
 endif()
-set(QUIC_BUILD_SHARED ON CACHE BOOL "Builds MsQuic as a dynamic library")
-set(QUIC_ENABLE_LOGGING ON CACHE BOOL "Enable MsQuic logging")
-add_subdirectory(msquic)
 
 # Build msh3 library (and cmd line tool).
 add_subdirectory(lib)

lib/msh3-config.cmake.in

@@ -3,6 +3,9 @@ if(NOT "@BUILD_SHARED_LIBS@")
     if("@MSH3_USE_EXTERNAL_LSQPACK@")
         find_dependency(ls-qpack CONFIG)
     endif()
+    if("@MSH3_USE_EXTERNAL_MSQUIC@")
+        find_dependency(msquic CONFIG)
+    endif()
 endif()
 
 include("${CMAKE_CURRENT_LIST_DIR}/msh3.cmake")