Add cmake cache var to allow for use of system openssl

package-system/OpenSSL/FindOpenSSL.cmake.Linux.template

@@ -0,0 +1,92 @@
+#
+# Copyright (c) Contributors to the Open 3D Engine Project.
+# For complete copyright and license terms please see the LICENSE at the root of this distribution.
+# 
+# SPDX-License-Identifier: Apache-2.0 OR MIT
+#
+#
+
+set(OPENSSL_O3DE_NAMESPACE "3rdParty::OpenSSL")
+if (TARGET $${OPENSSL_O3DE_NAMESPACE})
+    return()
+endif()
+
+set(SSL_TARGETNAME "OpenSSL::SSL")
+set(CRYPTO_TARGETNAME "OpenSSL::Crypto")
+
+if (LY_SYSTEM_PACKAGE_OpenSSL)
+
+    # We need to temporarily override the CMAKE_MODULE_PATH to force it to search in the system directories
+    set(CMAKE_MODULE_PATH_TMP $${CMAKE_MODULE_PATH})
+    set(CMAKE_MODULE_PATH "")
+    find_package(OpenSSL)
+    set(CMAKE_MODULE_PATH $${CMAKE_MODULE_PATH_TMP})
+
+    if (NOT OpenSSL_FOUND)
+       message(FATAL_ERROR "Compiling on linux requires the development headers for OpenSSL.  Try using your package manager to install the OpenSSL development libraries following https://wiki.openssl.org/index.php/Libssl_API")
+    else()
+        # OpenSSL targets should be considered as provided by the system
+        set_target_properties(OpenSSL::SSL OpenSSL::Crypto PROPERTIES LY_SYSTEM_LIBRARY TRUE)
+
+        # Alias the O3DE name to the official name
+        add_library(3rdParty::OpenSSL ALIAS OpenSSL::SSL)
+    endif()
+
+else()
+
+    # we're trying to be a drop-in replacement for the FindOpenSSL.cmake that is shipped
+    # with CMake itself, so we set the same variables with the same uppercase for compatibility
+    # for questions about these variables, see https://cmake.org/cmake/help/latest/module/FindOpenSSL.html
+    set(OPENSSL_FOUND True)
+    set(OPENSSL_INCLUDE_DIR $${CMAKE_CURRENT_LIST_DIR}/OpenSSL/include)
+    # c-only packages can be released containing only Release executables
+    set(OPENSSL_LIBS_DIR $${CMAKE_CURRENT_LIST_DIR}/OpenSSL/lib)
+    set(OPENSSL_CRYPTO_LIBRARY $${OPENSSL_LIBS_DIR}/libcrypto$${CMAKE_STATIC_LIBRARY_SUFFIX})
+    set(OPENSSL_CRYPTO_LIBRARIES
+        $${OPENSSL_CRYPTO_LIBRARY}
+        ${CRYPTO_LIBRARY_DEPENDENCIES})
+    set(OPENSSL_SSL_LIBRARY $${OPENSSL_LIBS_DIR}/libssl$${CMAKE_STATIC_LIBRARY_SUFFIX})
+    set(OPENSSL_SSL_LIBRARIES 
+        $${OPENSSL_SSL_LIBRARY}
+        $${OPENSSL_CRYPTO_LIBRARIES})
+    set(OPENSSL_LIBRARIES $${OPENSSL_SSL_LIBRARIES})
+    set(OPENSSL_VERSION "${OPENSSL_VERSION_STRING}")
+
+    add_library($${CRYPTO_TARGETNAME} STATIC IMPORTED GLOBAL)
+    set_target_properties($${CRYPTO_TARGETNAME} PROPERTIES IMPORTED_LINK_INTERFACE_LANGUAGES "C")
+    set_target_properties($${CRYPTO_TARGETNAME} PROPERTIES IMPORTED_LOCATION "$${OPENSSL_CRYPTO_LIBRARY}")
+
+    # anyone who links to the CRYPTO target also links to its dependencies:
+    target_link_libraries($${CRYPTO_TARGETNAME} INTERFACE ${CRYPTO_LIBRARY_DEPENDENCIES})
+
+    add_library($${SSL_TARGETNAME} STATIC IMPORTED GLOBAL)
+    set_target_properties($${SSL_TARGETNAME} PROPERTIES IMPORTED_LINK_INTERFACE_LANGUAGES "C")
+    set_target_properties($${SSL_TARGETNAME} PROPERTIES IMPORTED_LOCATION "$${OPENSSL_SSL_LIBRARY}")
+
+    # anyone who links to the SSL target also links to CRYPTO since SSL depends on CRYPTO:
+    target_link_libraries($${SSL_TARGETNAME} INTERFACE $${CRYPTO_TARGETNAME})
+
+    # cmake < 3.21 and visual studio < 16.10 don't properly implement SYSTEM includes
+    # so we use O3DEs patched implementation if it is available and fallback to default if not.
+    # this is futureproof so that when O3DE no longer needs to define this and CMake's system 
+    # works without fixes, O3DE can erase this implementation and this script will still function.
+    if (COMMAND ly_target_include_system_directories)
+        ly_target_include_system_directories(TARGET $${SSL_TARGETNAME} INTERFACE $${OPENSSL_INCLUDE_DIR})
+        ly_target_include_system_directories(TARGET $${CRYPTO_TARGETNAME} INTERFACE $${OPENSSL_INCLUDE_DIR})
+    else()
+        target_include_directories($${SSL_TARGETNAME} SYSTEM INTERFACE $${OPENSSL_INCLUDE_DIR})
+        target_include_directories($${CRYPTO_TARGETNAME} SYSTEM INTERFACE $${OPENSSL_INCLUDE_DIR})
+    endif()
+
+    # alias the O3DE name to the official name:
+    add_library($${OPENSSL_O3DE_NAMESPACE} ALIAS $${SSL_TARGETNAME})
+
+    # if we're not in O3DE, it's also extremely helpful to show a message to logs that indicate that this
+    # library was successfully picked up, as opposed to the system one.
+    # A good way to know if you're in O3DE or not is that O3DE sets various cache variables before 
+    # calling find_package, specifically, LY_VERSION_ENGINE_NAME is always set very early:
+    if (NOT LY_VERSION_ENGINE_NAME)
+        message(STATUS "Using O3DE's OpenSSL ($${OPENSSL_VERSION}) from $${CMAKE_CURRENT_LIST_DIR}")
+    endif()
+
+endif() # LY_SYSTEM_PACKAGE_OpenSSL

package-system/OpenSSL/build_config.json

@@ -10,7 +10,7 @@
    "Platforms":{
       "Linux":{
          "Linux":{
-            "cmake_find_template":"FindOpenSSL.cmake.template",
+            "cmake_find_template":"FindOpenSSL.cmake.Linux.template",
             "custom_build_cmd": [
                "./build-linux.sh",
                "openssl_1_1_1t",
@@ -31,7 +31,7 @@
             }
          },
          "Linux-aarch64":{
-            "cmake_find_template":"FindOpenSSL.cmake.template",
+            "cmake_find_template":"FindOpenSSL.cmake.Linux.template",
             "custom_build_cmd": [
                "./build-linux.sh",
                "openssl_1_1_1t",