anchor.diff:  let
     inherit (lib) versionOlder optional optionals optionalString;
   
  -  generic = { version, sha256 }:
  +  generic = { version, sha256, extraBuildInputs ? [] }:
       let
         withIpRoute = stdenv.isLinux && (versionOlder version "2.5.4");
       in
  
positive.code:   openvpn_24 = generic {
      version = "2.4.12";
      sha256 = "1vjx82nlkxrgzfiwvmmlnz8ids5m2fiqz7scy1smh3j9jnf2v5b6";
    };
  
    openvpn = generic {
      version = "2.5.6";
      sha256 = "0gdd88rcan9vfiwkzsqn6fxxdim7kb1bsxrcra59c5xksprpwfik";
    };
  }
  
negative.code: 
          nativeBuildInputs = [ pkg-config ];
  
          buildInputs = [ lzo ]
            ++ optional stdenv.isLinux pam
            ++ optional withIpRoute iproute2
            ++ optional useSystemd systemd
            ++ optional pkcs11Support pkcs11helper
            ++ extraBuildInputs;
  
          configureFlags = optionals withIpRoute [
            "--enable-iproute2"
  