ocserv: init at 0.12.1 (#42871)

`ocserv` is a VPN server which follows the openconnect protocol
(https://github.com/openconnect/protocol). The packaging is slightly
inspired by the AUR version
(https://aur.archlinux.org/packages/ocserv/).

This patch initializes the package written in C, the man pages and a
module for a simple systemd unit to run the VPN server. The package
supports the following authentication methods for the server:

* `plain` (mostly username/password)
* `pam`

The third method (`radius`) is currently not supported since `nixpkgs`
misses a packaged client.

The module can be used like this:

``` nix
{
  services.ocserv = {
    enable = true;
    config = ''
      ...
    '';
  };
}
```

The option `services.ocserv.config` is required on purpose to
ensure that nobody just enables the service and experiences unexpected
side-effects on the system. For a full reference, please refer to the
man pages, the online docs or the example value.

The docs recommend to simply use `nobody` as user, so no extra user has
been added to the internal user list. Instead a configuration like
this can be used:

```
run-as-user = nobody
run-as-group = nogroup
```

/cc @tenten8401
Fixes #42594

2 files changed, 100 insertions, 0 deletions

diff --git a/nixos/modules/module-list.nix b/nixos/modules/module-list.nix
index e5dce84d6ee6..f5d94baf173c 100644
--- a/nixos/modules/module-list.nix
+++ b/nixos/modules/module-list.nix
@@ -543,6 +543,7 @@
   ./services/networking/ntopng.nix
   ./services/networking/ntpd.nix
   ./services/networking/nylon.nix
+  ./services/networking/ocserv.nix
   ./services/networking/oidentd.nix
   ./services/networking/openfire.nix
   ./services/networking/openntpd.nix
diff --git a/nixos/modules/services/networking/ocserv.nix b/nixos/modules/services/networking/ocserv.nix
new file mode 100644
index 000000000000..61473a9fabf9
--- /dev/null
+++ b/nixos/modules/services/networking/ocserv.nix
@@ -0,0 +1,99 @@
+{ config, pkgs, lib, ... }:
+
+with lib;
+
+let
+
+  cfg = config.services.ocserv;
+
+in
+
+{
+  options.services.ocserv = {
+    enable = mkEnableOption "ocserv";
+
+    config = mkOption {
+      type = types.lines;
+
+      description = ''
+        Configuration content to start an OCServ server.
+
+        For a full configuration reference,please refer to the online documentation
+        (https://ocserv.gitlab.io/www/manual.html), the openconnect
+        recipes (https://github.com/openconnect/recipes) or `man ocserv`.
+      '';
+
+      example = ''
+        # configuration examples from $out/doc without explanatory comments.
+        # for a full reference please look at the installed man pages.
+        auth = "plain[passwd=./sample.passwd]"
+        tcp-port = 443
+        udp-port = 443
+        run-as-user = nobody
+        run-as-group = nogroup
+        socket-file = /var/run/ocserv-socket
+        server-cert = certs/server-cert.pem
+        server-key = certs/server-key.pem
+        keepalive = 32400
+        dpd = 90
+        mobile-dpd = 1800
+        switch-to-tcp-timeout = 25
+        try-mtu-discovery = false
+        cert-user-oid = 0.9.2342.19200300.100.1.1
+        tls-priorities = "NORMAL:%SERVER_PRECEDENCE:%COMPAT:-VERS-SSL3.0"
+        auth-timeout = 240
+        min-reauth-time = 300
+        max-ban-score = 80
+        ban-reset-time = 1200
+        cookie-timeout = 300
+        deny-roaming = false
+        rekey-time = 172800
+        rekey-method = ssl
+        use-occtl = true
+        pid-file = /var/run/ocserv.pid
+        device = vpns
+        predictable-ips = true
+        default-domain = example.com
+        ipv4-network = 192.168.1.0
+        ipv4-netmask = 255.255.255.0
+        dns = 192.168.1.2
+        ping-leases = false
+        route = 10.10.10.0/255.255.255.0
+        route = 192.168.0.0/255.255.0.0
+        no-route = 192.168.5.0/255.255.255.0
+        cisco-client-compat = true
+        dtls-legacy = true
+
+        [vhost:www.example.com]
+        auth = "certificate"
+        ca-cert = certs/ca.pem
+        server-cert = certs/server-cert-secp521r1.pem
+        server-key = cersts/certs/server-key-secp521r1.pem
+        ipv4-network = 192.168.2.0
+        ipv4-netmask = 255.255.255.0
+        cert-user-oid = 0.9.2342.19200300.100.1.1
+      '';
+    };
+  };
+
+  config = mkIf cfg.enable {
+    environment.systemPackages = [ pkgs.ocserv ];
+    environment.etc."ocserv/ocserv.conf".text = cfg.config;
+
+    security.pam.services.ocserv = {};
+
+    systemd.services.ocserv = {
+      description = "OpenConnect SSL VPN server";
+      documentation = [ "man:ocserv(8)" ];
+      after = [ "dbus.service" "network-online.target" ];
+      wantedBy = [ "multi-user.target" ];
+
+      serviceConfig = {
+        PrivateTmp = true;
+        PIDFile = "/var/run/ocserv.pid";
+        ExecStart = "${pkgs.ocserv}/bin/ocserv --foreground --pid-file /var/run/ocesrv.pid --config /etc/ocserv/ocserv.conf";
+        ExecReload = "${pkgs.coreutils}/bin/kill -HUP $MAINPID";
+      };
+    };
+  };
+}