pub unsafe extern "C" fn coap_new_client_session_psk(
    ctx: *mut coap_context_t,
    local_if: *const coap_address_t,
    server: *const coap_address_t,
    proto: coap_proto_t,
    identity: *const c_char,
    key: *const u8,
    key_len: c_uint
) -> *mut coap_session_t