Add option to disable secret key generation

CMakeLists.txt

 cmake_minimum_required(VERSION 2.8)
 project(postsrsd C)
 
+option(GENERATE_SRS_SECRET "Generate a random SRS secret if none exists during install" ON)
+
 find_program(HELP2MAN help2man DOC "path to help2man executable")
 find_program(DD dd DOC "path to dd executable")
 find_program(BASE64 base64 DOC "path to base64 executable")

postinstall.cmake.in

+set(GENERATE_SRS_SECRET "@GENERATE_SRS_SECRET@")
 set(INIT_FLAVOR "@INIT_FLAVOR@")
 set(SECRET_FILE "@PROJECT_NAME@.secret")
 set(DD "@DD@")
 	file(INSTALL "@CMAKE_CURRENT_BINARY_DIR@/@PROJECT_NAME@.upstart" DESTINATION "/etc/init" RENAME "@PROJECT_NAME@.conf")
 endif()
 
-if(DD AND BASE64 AND EXISTS "/dev/urandom" AND NOT EXISTS "$ENV{DESTDIR}/etc/${SECRET_FILE}")
+if(GENERATE_SRS_SECRET AND DD AND BASE64 AND EXISTS "/dev/urandom" AND NOT EXISTS "$ENV{DESTDIR}/etc/${SECRET_FILE}")
 	message(STATUS "Generating secret key")
 	execute_process(
 		COMMAND ${DD} if=/dev/urandom bs=18 count=1