AC_DEFUN([TCLTLS_SSL_OPENSSL], [
	dnl Determine if pkg-config tool is available
	AC_CHECK_TOOL([PKG_CONFIG], [pkg-config])

	dnl Enable support for SSL 3.0 protocol
	AC_ARG_ENABLE([ssl3], AS_HELP_STRING([--disable-ssl3], [disable SSL3 protocol]), [
		if test "$enableval" == "no"; then
			AC_DEFINE([NO_SSL3], [1], [Disable SSL3 protocol])
			AC_MSG_CHECKING([for disable SSL3 protocol])
			AC_MSG_RESULT([yes])
		fi
	], AC_DEFINE([NO_SSL3], [1], [Disable SSL3 protocol]))

	dnl Disable support for TLS 1.0 protocol
	AC_ARG_ENABLE([tls1], AS_HELP_STRING([--disable-tls1], [disable TLS1 protocol]), [
		if test "$enableval" == "no"; then
			AC_DEFINE([NO_TLS1], [1], [Disable TLS1 protocol])
			AC_MSG_CHECKING([for disable TLS1 protocol])
			AC_MSG_RESULT([yes])
		fi
	])

	dnl Disable support for TLS 1.1 protocol
	AC_ARG_ENABLE([tls1_1], AS_HELP_STRING([--disable-tls1_1], [disable TLS1.1 protocol]), [
		if test "$enableval" == "no"; then
			AC_DEFINE([NO_TLS1_1], [1], [Disable TLS1.1 protocol])
			AC_MSG_CHECKING([for disable TLS1.1 protocol])
			AC_MSG_RESULT([yes])
		fi
	])

	dnl Disable support for TLS 1.2 protocol
	AC_ARG_ENABLE([tls1_2], AS_HELP_STRING([--disable-tls1_2], [disable TLS1.2 protocol]), [
		if test "$enableval" == "no"; then
			AC_DEFINE([NO_TLS1_2], [1], [Disable TLS1.2 protocol])
			AC_MSG_CHECKING([for disable TLS1.2 protocol])
			AC_MSG_RESULT([yes])
		fi
	])

	dnl Disable support for TLS 1.3 protocol
	AC_ARG_ENABLE([tls1_3], AS_HELP_STRING([--disable-tls1_3], [disable TLS1.3 protocol]), [
		if test "$enableval" == "no"; then
			AC_DEFINE([NO_TLS1_3], [1], [Disable TLS1.3 protocol])
			AC_MSG_CHECKING([for disable TLS1.3 protocol])
			AC_MSG_RESULT([yes])
		fi
	])

	)
	AC_MSG_CHECKING([for OpenSSL include directory])
	AC_MSG_RESULT($opensslincludedir)

	dnl Set SSL include variables
	if test -n "$opensslincludedir"; then
		AC_MSG_CHECKING([for ssl.h])
		if test -f "${opensslincludedir}/openssl/ssl.h"; then
			TCLTLS_SSL_CFLAGS="-I$opensslincludedir"
			TCLTLS_SSL_INCLUDES="-I$opensslincludedir"
			AC_MSG_RESULT([yes])
		else
			AC_MSG_RESULT([no])
			AC_MSG_ERROR([Unable to locate ssl.h])
		fi
	fi

	dnl Set SSL lib files path
	AC_ARG_WITH([openssl-libdir],
		AS_HELP_STRING([--with-openssl-libdir=<dir>],
			[path to lib directory of OpenSSL or LibreSSL installation]
		), [
			openssllibdir="$withval"
		], [
			if test -n "$openssldir"; then
				if test "$do64bit" == 'yes' -a -d ${openssldir}/lib64; then
					openssllibdir="$openssldir/lib64"
				else
					openssllibdir="$openssldir/lib"
				fi
			else
				openssllibdir=''
			fi
		]
	)
	AC_MSG_CHECKING([for OpenSSL lib directory])
	AC_MSG_RESULT($openssllibdir)

	dnl Set SSL lib variables
	SSL_LIBS_PATH=''
	if test -n "$openssllibdir"; then
		if test "$TCLEXT_TLS_STATIC_SSL" == 'no'; then
			LIBEXT=${SHLIB_SUFFIX}
		else
			LIBEXT='.a'
		fi

		if test -f "${openssllibdir}/libssl${LIBEXT}"; then
			SSL_LIBS_PATH="-L$openssllibdir"
		else
			AC_MSG_ERROR([Unable to locate libssl${LIBEXT}])
		fi
	fi

	dnl Set location of pkgconfig files

				opensslpkgconfigdir=''
			fi
		]
	)
	AC_MSG_CHECKING([for OpenSSL pkgconfig])
	AC_MSG_RESULT($opensslpkgconfigdir)

	dnl Use pkg-config to find OpenSSL if not already found 
	if test -n "$PKG_CONFIG" -a -z "$openssldir" -a -z "$opensslincludedir" -a -z "$openssllibdir"; then
	    USE_PKG_CONFIG=`"${PKG_CONFIG}" --list-all | grep openssl`

	    dnl Use pkg-config to find the library names
	    if test -n "$USE_PKG_CONFIG"; then
		dnl Temporarily update PKG_CONFIG_PATH
		PKG_CONFIG_PATH_SAVE="${PKG_CONFIG_PATH}"
		if test -n "$opensslpkgconfigdir"; then
			if ! test -f "${opensslpkgconfigdir}/openssl.pc"; then
				AC_MSG_ERROR([Unable to locate ${opensslpkgconfigdir}/openssl.pc])
			fi

			PKG_CONFIG_PATH="${opensslpkgconfigdir}:${PKG_CONFIG_PATH}"
			export PKG_CONFIG_PATH
		fi

		pkgConfigExtraArgs=''
		if test "$SHARED_BUILD" == "0" -o "$TCLEXT_TLS_STATIC_SSL" == 'yes'; then
			pkgConfigExtraArgs='--static'
		fi

		if test -z "$TCLTLS_SSL_LIBS"; then
			TCLTLS_SSL_LIBS="$SSL_LIBS_PATH `${PKG_CONFIG} openssl --libs $pkgConfigExtraArgs`" || AC_MSG_ERROR([Unable to get OpenSSL Configuration])
			if test "${TCLEXT_TLS_STATIC_SSL}" == 'yes'; then
				TCLTLS_SSL_LIBS="-Wl,-Bstatic $TCLTLS_SSL_LIBS -Wl,-Bdynamic"
			fi
		fi
		if test -z "$TCLTLS_SSL_CFLAGS"; then
			TCLTLS_SSL_CFLAGS="`"${PKG_CONFIG}" openssl --cflags-only-other $pkgConfigExtraArgs`" || AC_MSG_ERROR([Unable to get OpenSSL Configuration])
		fi
		if test -z "$TCLTLS_SSL_INCLUDES"; then
			TCLTLS_SSL_INCLUDES="`"${PKG_CONFIG}" openssl --cflags-only-I $pkgConfigExtraArgs`" || AC_MSG_ERROR([Unable to get OpenSSL Configuration])
		fi
		PKG_CONFIG_PATH="${PKG_CONFIG_PATH_SAVE}"
	    fi
	fi

	dnl Use fall-back settings for OpenSSL include and library paths
	if test -z "$TCLTLS_SSL_CFLAGS"; then
		TCLTLS_SSL_CFLAGS=""
	fi
	if test -z "$TCLTLS_SSL_INCLUDES"; then
		if test -f /usr/include/openssl/ssl.h; then
			TCLTLS_SSL_INCLUDES="-I/usr/include"
		fi
	fi
	if test -z "$TCLTLS_SSL_LIBS"; then
		if test "$TCLEXT_TLS_STATIC_SSL" == 'no'; then
		    TCLTLS_SSL_LIBS="$SSL_LIBS_PATH -lssl -lcrypto"
		else
		    # Linux and Solaris
		    TCLTLS_SSL_LIBS="$SSL_LIBS_PATH -Wl,-Bstatic -lssl -lcrypto -Wl,-Bdynamic"
		    # HPUX: -Wl,-a,archive ... -Wl,-a,shared_archive
		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])
])