Add Caddyfile support for sip_guardian_admin HTTP handler

Register handler directive with httpcaddyfile and implement
UnmarshalCaddyfile to enable Caddyfile configuration syntax.

admin.go

@@ -6,11 +6,21 @@ import (
 	"strings"
 
 	"github.com/caddyserver/caddy/v2"
+	"github.com/caddyserver/caddy/v2/caddyconfig/caddyfile"
+	"github.com/caddyserver/caddy/v2/caddyconfig/httpcaddyfile"
 	"github.com/caddyserver/caddy/v2/modules/caddyhttp"
 )
 
 func init() {
 	caddy.RegisterModule(AdminHandler{})
+	httpcaddyfile.RegisterHandlerDirective("sip_guardian_admin", parseSIPGuardianAdmin)
+}
+
+// parseSIPGuardianAdmin parses the sip_guardian_admin directive
+func parseSIPGuardianAdmin(h httpcaddyfile.Helper) (caddyhttp.MiddlewareHandler, error) {
+	var handler AdminHandler
+	err := handler.UnmarshalCaddyfile(h.Dispenser)
+	return &handler, err
 }
 
 // AdminHandler provides HTTP endpoints to manage SIP Guardian
@@ -160,8 +170,30 @@ func (h *AdminHandler) handleBan(w http.ResponseWriter, r *http.Request, path st
 	})
 }
 
+// UnmarshalCaddyfile implements caddyfile.Unmarshaler for AdminHandler.
+// Usage in Caddyfile:
+//
+//	handle /api/sip-guardian/* {
+//	    sip_guardian_admin
+//	}
+//
+// Or simply: sip_guardian_admin
+func (h *AdminHandler) UnmarshalCaddyfile(d *caddyfile.Dispenser) error {
+	// Move past "sip_guardian_admin" token
+	d.Next()
+
+	// This handler doesn't have any configuration options currently
+	// but we need to consume any block if present
+	for nesting := d.Nesting(); d.NextBlock(nesting); {
+		return d.Errf("unknown sip_guardian_admin directive: %s", d.Val())
+	}
+
+	return nil
+}
+
 // Interface guards
 var (
 	_ caddyhttp.MiddlewareHandler = (*AdminHandler)(nil)
 	_ caddy.Provisioner           = (*AdminHandler)(nil)
+	_ caddyfile.Unmarshaler       = (*AdminHandler)(nil)
 )