AC_ARG_WITH([openssl-includedir],
		AS_HELP_STRING([--with-openssl-includedir=<dir>],
			[path to include directory of OpenSSL or LibreSSL installation]
		), [
			opensslincludedir="$withval"
		], [
			if test ! -z "$openssldir"; then
				if test -f "${openssldir}/include/openssl/ssl.h"; then
					opensslincludedir="${openssldir}/include/openssl"
				else
					opensslincludedir="${openssldir}/include"
				opensslincludedir="${openssldir}/include"
				fi
			else
				opensslincludedir=''
			fi
		]
	)
	AC_MSG_CHECKING([for OpenSSL include directory])
	AC_MSG_RESULT($opensslincludedir)

	dnl Set SSL include vars
	if test ! -z "$opensslincludedir"; then
		if test -f "$opensslincludedir/ssl.h"; then
		if test -f "$opensslincludedir/openssl/ssl.h"; then
			TCLTLS_SSL_CFLAGS="-I$opensslincludedir"
			TCLTLS_SSL_INCLUDES="-I$opensslincludedir"
			AC_MSG_CHECKING([for ssl.h])
			AC_MSG_RESULT([yes])
		else
			AC_MSG_CHECKING([for ssl.h])
			AC_MSG_RESULT([no])

	if test -z "$TCLTLS_SSL_LIBS"; then
		TCLTLS_SSL_LIBS="-lcrypto -lssl"
	fi
	if test -z "$TCLTLS_SSL_CFLAGS"; then
		TCLTLS_SSL_CFLAGS=""
	fi
	if test -z "$TCLTLS_SSL_INCLUDES"; then
		if test -d /usr/include/openssl; then
		if test -f /usr/include/openssl/ssl.h; then
			TCLTLS_SSL_INCLUDES="-I/usr/include/openssl"
		else
			TCLTLS_SSL_INCLUDES="-I/usr/include"
		fi
	fi

	dnl Include config variables in --help list and make available to be substituted via AC_SUBST.
	AC_ARG_VAR([TCLTLS_SSL_CFLAGS], [C compiler flags for OpenSSL or LibreSSL])
	AC_ARG_VAR([TCLTLS_SSL_INCLUDES], [C compiler include paths for OpenSSL or LibreSSL])
	AC_ARG_VAR([TCLTLS_SSL_LIBS], [libraries to pass to the linker for OpenSSL or LibreSSL])
])