Initial implementation

.gitignore

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+# Binaries for programs and plugins
+*.exe
+*.exe~
+*.dll
+*.so
+*.dylib
+
+# Test binary, built with `go test -c`
+*.test
+
+# Output of the go coverage tool, specifically when used with LiteIDE
+*.out
+
+# Dependency directories (remove the comment below to include it)
+# vendor/

README.md

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+Duck DNS module for Caddy
+===========================
+
+This package contains a DNS provider module for [Caddy](https://github.com/caddyserver/caddy). It can be used to manage DNS records for Duck DNS.
+
+## Caddy module name
+
+```
+dns.providers.duckdns
+```
+
+## Config examples
+
+To use this module for the ACME DNS challenge, [configure the ACME issuer in your Caddy JSON](https://caddyserver.com/docs/json/apps/tls/automation/policies/issuer/acme/) like so:
+
+```
+{
+	"module": "acme",
+	"challenges": {
+		"dns": {
+			"provider": {
+				"name": "duckdns",
+				"api_token": "YOUR_DUCKDNS_API_TOKEN"
+			}
+		}
+	}
+}
+```
+
+or with the Caddyfile:
+
+```
+tls {
+	dns cloudflare {env.DUCKDNS_API_TOKEN}
+}
+```
+
+You can replace `{env.DUCKDNS_API_TOKEN}` with the actual auth token if you prefer to put it directly in your config instead of an environment variable.
+
+
+## Authenticating
+
+See [the associated README in the libdns package](https://github.com/libdns/duckdns) for important information about credentials. Your token can be found at the top of the page when logged in at https://www.duckdns.org.

duckdns.go

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+package duckdns
+
+import (
+	"github.com/caddyserver/caddy/v2"
+	"github.com/caddyserver/caddy/v2/caddyconfig/caddyfile"
+	"github.com/libdns/duckdns"
+)
+
+// Provider wraps the provider implementation as a Caddy module.
+type Provider struct{ *duckdns.Provider }
+
+func init() {
+	caddy.RegisterModule(Provider{})
+}
+
+// CaddyModule returns the Caddy module information.
+func (Provider) CaddyModule() caddy.ModuleInfo {
+	return caddy.ModuleInfo{
+		ID:  "dns.providers.duckdns",
+		New: func() caddy.Module { return &Provider{new(duckdns.Provider)} },
+	}
+}
+
+// UnmarshalCaddyfile sets up the DNS provider from Caddyfile tokens. Syntax:
+//
+// duckdns [<api_token>] {
+//     api_token <api_token>
+// }
+//
+func (p *Provider) UnmarshalCaddyfile(d *caddyfile.Dispenser) error {
+	repl := caddy.NewReplacer()
+	for d.Next() {
+		if d.NextArg() {
+			p.Provider.APIToken = repl.ReplaceAll(d.Val(), "")
+		}
+		if d.NextArg() {
+			return d.ArgErr()
+		}
+		for nesting := d.Nesting(); d.NextBlock(nesting); {
+			switch d.Val() {
+			case "api_token":
+				if p.Provider.APIToken != "" {
+					return d.Err("API token already set")
+				}
+				p.Provider.APIToken = repl.ReplaceAll(d.Val(), "")
+				if d.NextArg() {
+					return d.ArgErr()
+				}
+			default:
+				return d.Errf("unrecognized subdirective '%s'", d.Val())
+			}
+		}
+	}
+	if p.Provider.APIToken == "" {
+		return d.Err("missing API token")
+	}
+	return nil
+}
+
+// Interface guard
+var _ caddyfile.Unmarshaler = (*Provider)(nil)

go.mod

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+module github.com/caddy-dns/duckdns
+
+go 1.15
+
+require (
+	github.com/caddyserver/caddy/v2 v2.2.3
+	github.com/libdns/duckdns v0.0.0-20201222042124-b3088d77f212
+)