feat: add CrowdSec security module

- Wraps native NixOS CrowdSec service
- Configures SSH and nginx log acquisition
- Installs linux/nginx/sshd hub collections
- Supports IP whitelisting and ban duration config
- Optional nginx bouncer integration (requires manual API key setup)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

modules/crowdsec.nix

@@ -0,0 +1,138 @@
+# CrowdSec Module
+# Provides: Collaborative intrusion detection and prevention
+#
+# Usage:
+#   myModules.crowdsec = {
+#     enable = true;
+#     enableNginxBouncer = true;  # Block attackers at nginx level
+#   };
+
+{
+  config,
+  lib,
+  ...
+}:
+
+let
+  cfg = config.myModules.crowdsec;
+in
+{
+  options.myModules.crowdsec = {
+    enable = lib.mkEnableOption "CrowdSec security engine";
+
+    enableNginxBouncer = lib.mkOption {
+      type = lib.types.bool;
+      default = true;
+      description = "Enable nginx bouncer to block malicious IPs at nginx level";
+    };
+
+    whitelistIPs = lib.mkOption {
+      type = lib.types.listOf lib.types.str;
+      default = [ ];
+      example = [ "1.2.3.4" "10.0.0.0/8" ];
+      description = "IP addresses or CIDR ranges to whitelist";
+    };
+
+    banDuration = lib.mkOption {
+      type = lib.types.str;
+      default = "4h";
+      description = "Default ban duration for malicious IPs";
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    services.crowdsec = {
+      enable = true;
+      autoUpdateService = true;
+
+      # Enable Local API for bouncers
+      settings.general.api.server.enable = true;
+
+      # Log acquisitions
+      localConfig.acquisitions = [
+        # SSH logs
+        {
+          source = "journalctl";
+          journalctl_filter = [ "_SYSTEMD_UNIT=sshd.service" ];
+          labels = {
+            type = "syslog";
+          };
+        }
+        # Nginx access logs
+        {
+          source = "journalctl";
+          journalctl_filter = [ "_SYSTEMD_UNIT=nginx.service" ];
+          labels = {
+            type = "nginx";
+          };
+        }
+      ];
+
+      # Whitelist parser for trusted IPs
+      localConfig.parsers.s02Enrich = lib.mkIf (cfg.whitelistIPs != [ ]) [
+        {
+          name = "nixos/whitelist";
+          description = "Whitelist trusted IPs";
+          whitelist = {
+            reason = "Trusted IPs";
+            ip = lib.filter (ip: !(lib.hasInfix "/" ip)) cfg.whitelistIPs;
+            cidr = lib.filter (lib.hasInfix "/") cfg.whitelistIPs;
+          };
+        }
+      ];
+
+      # Remediation profiles
+      localConfig.profiles = [
+        {
+          name = "default_ip_remediation";
+          filters = [ "Alert.Remediation == true && Alert.GetScope() == 'Ip'" ];
+          decisions = [
+            {
+              type = "ban";
+              duration = cfg.banDuration;
+            }
+          ];
+          on_success = "break";
+        }
+      ];
+
+      # Hub collections for common attack patterns
+      hub = {
+        collections = [
+          "crowdsecurity/linux"
+          "crowdsecurity/nginx"
+          "crowdsecurity/sshd"
+        ];
+      };
+    };
+
+    # Nginx bouncer integration
+    # Note: This requires the crowdsec-nginx-bouncer package
+    # which may need to be installed separately
+    services.nginx = lib.mkIf cfg.enableNginxBouncer {
+      # Add crowdsec bouncer configuration
+      # The bouncer checks with CrowdSec LAPI before allowing requests
+      upstreams.crowdsec-squid = {
+        servers = {
+          "127.0.0.1:8081" = { };
+        };
+      };
+
+      # Include bouncer in all virtual hosts
+      appendHttpConfig = ''
+        # CrowdSec bouncer will be configured via environment
+        # cscli bouncers add nginx-bouncer --key <generated-key>
+      '';
+    };
+
+    # Instructions for manual setup (bouncer requires API key)
+    system.activationScripts.crowdsec-nginx-info = lib.mkIf cfg.enableNginxBouncer ''
+      echo ""
+      echo "=== CrowdSec Setup ==="
+      echo "To enable nginx bouncer, run:"
+      echo "  sudo cscli bouncers add nginx-bouncer --key \$(openssl rand -hex 32)"
+      echo "Then configure /etc/crowdsec/bouncers/crowdsec-nginx-bouncer.conf"
+      echo ""
+    '';
+  };
+}