Add symmetric keys example (CA-14)

[Darkenkade42]

Added an example to demonstrate device provisioning with symmetric keys.

[CLAassistant]

All committers have signed the CLA.

[Lisa999]

There's a bug in your code if you're using CMake! The file port / CMakeLists.txt need to be changed also:
From:

if (CONFIG_DEVICE_COMMON_NAME)
	list (APPEND COMPONENT_SRCS "${AZURE_IOT_SDK}/provisioning_client/src/iothub_auth_client.c")
endif()

set (COMPONENT_SUBMODULES "${AZURE_IOT_SDK}")

set(COMPONENT_PRIV_REQUIRES "mbedtls esp-tls main")

register_component()

set_source_files_properties(
    ${AZURE_IOT_SDK}/iothub_client/src/iothubtransport_mqtt_common.c
    PROPERTIES COMPILE_FLAGS
    -Wno-maybe-uninitialized)

component_compile_options (
	-Wno-unused-function
	-Wno-missing-braces
	-Wno-missing-field-initializers
	)

component_compile_definitions (
    USE_LWIP_SOCKET_FOR_AZURE_IOT
	HSM_TYPE_X509
	HSM_TYPE_SAS_TOKEN
)

if (CONFIG_DEVICE_COMMON_NAME)
	add_definitions(-DUSE_PROV_MODULE)
endif()

to this:

if (CONFIG_DEVICE_COMMON_NAME)
	list (APPEND COMPONENT_SRCS "${AZURE_IOT_SDK}/provisioning_client/src/iothub_auth_client.c")
endif()

if (CONFIG_SYMM_KEY)
	list (APPEND COMPONENT_SRCS "${AZURE_IOT_SDK}/provisioning_client/src/iothub_auth_client.c")
endif()

set (COMPONENT_SUBMODULES "${AZURE_IOT_SDK}")

set(COMPONENT_PRIV_REQUIRES "mbedtls esp-tls main")

register_component()

component_compile_options (
	-Wno-unused-function
	-Wno-missing-braces
	-Wno-missing-field-initializers
	)

component_compile_definitions (
        USE_LWIP_SOCKET_FOR_AZURE_IOT
	HSM_TYPE_SAS_TOKEN
)

if (CONFIG_DEVICE_COMMON_NAME)
	add_definitions(-DUSE_PROV_MODULE -DHSM_TYPE_X509)
endif()

if (CONFIG_SYMM_KEY)
	add_definitions(-DUSE_PROV_MODULE -DHSM_TYPE_SYMM_KEY)
endif()

This prevents the linker error:

undefined reference to `hsm_client_x509_init'

[Darkenkade42]

You are correct @Lisa999 . I have added your proposed changes.