Check for openssl binary in configure, don't fail if not found

Prefer openssl binary from the same location as the openssl library.

Make it possible to suppress certificate generation during install by
passing OPENSSL=: to make.

configure.ac

@@ -140,6 +140,10 @@ AC_SUBST(DLOPEN_LIBS)
 PKG_CHECK_MODULES([OPENSSL], [openssl >= 0], [],
   [AC_MSG_ERROR([please install libssl-dev or openssl-devel])])
 
+# look for openssl binary
+OPENSSL_BIN=`$PKG_CONFIG --variable=exec_prefix openssl`/bin
+AC_PATH_PROGS([OPENSSL], [openssl], [:], [$OPENSSL_BIN:$PATH])
+
 # checking for pam variation
 # Linux-PAM is used in Linux systems
 # OpenPAM is used by FreeBSD, NetBSD, DragonFly BSD and OS X

keygen/Makefile.am

@@ -23,7 +23,7 @@ install-data-hook:
 	  ./xrdp-keygen xrdp $(DESTDIR)$(xrdpsysconfdir)/rsakeys.ini; \
 	fi && \
 	if [ ! -f $(DESTDIR)$(xrdpsysconfdir)/cert.pem ]; then \
-	  openssl req -x509 -newkey rsa:2048 -sha256 -nodes \
+	  $(OPENSSL) req -x509 -newkey rsa:2048 -sha256 -nodes \
 	    -keyout $(DESTDIR)$(xrdpsysconfdir)/key.pem -out \
 	    $(DESTDIR)$(xrdpsysconfdir)/cert.pem -days 365 \
 	    -subj /C=US/ST=CA/L=Sunnyvale/O=xrdp/CN=www.xrdp.org \