diff --git a/environments/arm-linux/default_toolchain_file.cmake b/environments/arm-linux/default_toolchain_file.cmake
index d530b0d..7ac1621 100644
--- a/environments/arm-linux/default_toolchain_file.cmake
+++ b/environments/arm-linux/default_toolchain_file.cmake
@@ -16,3 +16,4 @@
 set(CMAKE_CXX_FLAGS_INIT "-fdiagnostics-show-option -gdwarf-2 -mstrict-align -O0 -DARM64=1")
 
 include($ENV{TS_ROOT}/tools/cmake/compiler/GCC.cmake REQUIRED)
+include($ENV{TS_ROOT}/tools/cmake/compiler/config_iface.cmake REQUIRED)
diff --git a/environments/linux-pc/default_toolchain_file.cmake b/environments/linux-pc/default_toolchain_file.cmake
index 93e716f..6978dbf 100644
--- a/environments/linux-pc/default_toolchain_file.cmake
+++ b/environments/linux-pc/default_toolchain_file.cmake
@@ -1,8 +1,8 @@
 #-------------------------------------------------------------------------------
-# Copyright (c) 2020, Arm Limited and Contributors. All rights reserved.
+# Copyright (c) 2020-2021, Arm Limited and Contributors. All rights reserved.
 #
 # SPDX-License-Identifier: BSD-3-Clause
 #
 #-------------------------------------------------------------------------------
 
-# Empty.
+include($ENV{TS_ROOT}/tools/cmake/compiler/config_iface.cmake REQUIRED)
diff --git a/environments/opteesp/default_toolchain_file.cmake b/environments/opteesp/default_toolchain_file.cmake
index c73345f..34ca0c9 100644
--- a/environments/opteesp/default_toolchain_file.cmake
+++ b/environments/opteesp/default_toolchain_file.cmake
@@ -20,7 +20,7 @@
 #set(CMAKE_EXE_LINKER_FLAGS_INIT --specs=nosys.specs)
 
 include($ENV{TS_ROOT}/tools/cmake/compiler/GCC.cmake REQUIRED)
-
+include($ENV{TS_ROOT}/tools/cmake/compiler/config_iface.cmake REQUIRED)
 # Set mandatory compiler and linker flags for this environment:
 #   - This environment uses a libc implementation from SPDEV-KIT. Disable standard
 #     include search paths, startup files and default libraries.
diff --git a/external/MbedTLS/MbedTLS.cmake b/external/MbedTLS/MbedTLS.cmake
index 45c1251..041af5c 100644
--- a/external/MbedTLS/MbedTLS.cmake
+++ b/external/MbedTLS/MbedTLS.cmake
@@ -57,42 +57,25 @@
 set(PSA_CRYPTO_API_INCLUDE "${MBEDTLS_INSTALL_PATH}/include" CACHE STRING "PSA Crypto API include path")
 
 #Configure the library
-if(NOT CMAKE_CROSSCOMPILING)
-	execute_process(COMMAND
-		${CMAKE_COMMAND}
-			-DENABLE_PROGRAMS=OFF
-			-DENABLE_TESTING=OFF
-			-DUNSAFE_BUILD=ON
-			-DCMAKE_INSTALL_PREFIX=${MBEDTLS_INSTALL_PATH}
-			-DCMAKE_TOOLCHAIN_FILE=${TS_EXTERNAL_LIB_TOOLCHAIN_FILE}
-			-Dthirdparty_def=-DMBEDTLS_USER_CONFIG_FILE="${MBEDTLS_USER_CONFIG_FILE}"
-			-Dthirdparty_inc=${MBEDTLS_EXTRA_INCLUDES}
-			-GUnix\ Makefiles
-			${mbedtls_SOURCE_DIR}
-		WORKING_DIRECTORY
-			${mbedtls_BINARY_DIR}
-		)
-else()
-	execute_process(COMMAND
-		${CMAKE_COMMAND}
-			-DENABLE_PROGRAMS=OFF
-			-DENABLE_TESTING=OFF
-			-DUNSAFE_BUILD=ON
-			-DCMAKE_INSTALL_PREFIX=${MBEDTLS_INSTALL_PATH}
-			-DCMAKE_TOOLCHAIN_FILE=${TS_EXTERNAL_LIB_TOOLCHAIN_FILE}
-			-DCMAKE_TRY_COMPILE_TARGET_TYPE=STATIC_LIBRARY
-			-Dthirdparty_def=-DMBEDTLS_USER_CONFIG_FILE="${MBEDTLS_USER_CONFIG_FILE}"
-			-Dthirdparty_inc=${MBEDTLS_EXTRA_INCLUDES}
-			-GUnix\ Makefiles
-			${mbedtls_SOURCE_DIR}
-		WORKING_DIRECTORY
-			${mbedtls_BINARY_DIR}
-		RESULT_VARIABLE _exec_error
-	)
+execute_process(COMMAND
+	${CMAKE_COMMAND}
+		-DENABLE_PROGRAMS=OFF
+		-DENABLE_TESTING=OFF
+		-DUNSAFE_BUILD=ON
+		-DCMAKE_INSTALL_PREFIX=${MBEDTLS_INSTALL_PATH}
+		-DCMAKE_TOOLCHAIN_FILE=${TS_EXTERNAL_LIB_TOOLCHAIN_FILE}
+		-DCMAKE_TRY_COMPILE_TARGET_TYPE=STATIC_LIBRARY
+		-DEXTERNAL_DEFINITIONS=-DMBEDTLS_USER_CONFIG_FILE="${MBEDTLS_USER_CONFIG_FILE}"
+		-DEXTERNAL_INCLUDE_PATHS=${MBEDTLS_EXTRA_INCLUDES}
+		-GUnix\ Makefiles
+		${mbedtls_SOURCE_DIR}
+	WORKING_DIRECTORY
+		${mbedtls_BINARY_DIR}
+	RESULT_VARIABLE _exec_error
+)
 
-	if (_exec_error)
-		message(FATAL_ERROR "Configuration step of Mbed TLS failed with ${_exec_error}.")
-	endif()
+if (_exec_error)
+	message(FATAL_ERROR "Configuration step of Mbed TLS failed with ${_exec_error}.")
 endif()
 
 #TODO: add dependency to generated project on this file!
diff --git a/tools/cmake/compiler/config_iface.cmake b/tools/cmake/compiler/config_iface.cmake
new file mode 100644
index 0000000..4afa799
--- /dev/null
+++ b/tools/cmake/compiler/config_iface.cmake
@@ -0,0 +1,15 @@
+#-------------------------------------------------------------------------------
+# Copyright (c) 2021, Arm Limited and Contributors. All rights reserved.
+#
+# SPDX-License-Identifier: BSD-3-Clause
+#
+#-------------------------------------------------------------------------------
+
+# This provides a common interface for injecting definitions and include paths
+# into a cmake build for the purpose of applying an externally defined
+# build configuration.  Although some cmake based external components provide
+# their own cmake based configuration interface, not all do.  This file gets
+# included by environment specific cmake toolchain files that get actioned
+# early on when a new cmake build context is created.
+add_definitions(${EXTERNAL_DEFINITIONS})
+include_directories(${EXTERNAL_INCLUDE_PATHS})