isync: add optional support for XOAUTH2 authentication method

pkgs/tools/networking/isync/default.nix

@@ -1,6 +1,7 @@
 { lib, stdenv, fetchurl, pkg-config, perl
 , openssl, db, cyrus_sasl, zlib
 , Security
+, withCyrusSaslXoauth2 ? true, cyrus-sasl-xoauth2, makeWrapper
 }:
 
 stdenv.mkDerivation rec {
@@ -20,10 +21,16 @@ stdenv.mkDerivation rec {
     ./work-around-unexpected-EOF-error-messages-at-end-of-SSL-connections.patch
   ];
 
-  nativeBuildInputs = [ pkg-config perl ];
+  nativeBuildInputs = [ pkg-config perl ]
+    ++ lib.optionals withCyrusSaslXoauth2 [ makeWrapper ];
   buildInputs = [ openssl db cyrus_sasl zlib ]
     ++ lib.optionals stdenv.isDarwin [ Security ];
 
+  postInstall = lib.optionalString withCyrusSaslXoauth2 ''
+    wrapProgram "$out/bin/mbsync" \
+        --prefix SASL_PATH : "${lib.makeSearchPath "lib/sasl2" [ cyrus-sasl-xoauth2 ]}"
+  '';
+
   meta = with lib; {
     homepage = "http://isync.sourceforge.net/";
     # https://sourceforge.net/projects/isync/