$ show go-acme/lego
This repository implements 'lego', a production-grade ACME client written in Go for automating SSL/TLS certificate issuance and renewal with Let's Encrypt and other ACME-compliant Certificate Authorities. The system operates as both a CLI tool and a reusable library, supporting the full ACME protocol (RFC 8555) including account registration, order creation, challenge solving (HTTP-01, DNS-01, TLS-ALPN-01, and experimental DNS-PERSIST-01), certificate download, and lifecycle management (renewal, revocation, archival). Architecturally, the codebase is modular: a core ACME API client (`acme/api/`) handles protocol interactions; challenge solvers (`challenge/`) implement domain validation strategies; a plugin-style DNS provider system (`providers/dns/`) integrates with over 200 DNS service APIs for automated DNS-01 challenge resolution; a CLI layer (`cmd/`) provides subcommands for run, certificates, accounts, archives, and migration; and storage (`cmd/internal/storage/`) persists certificates, keys, and account data to disk. Configuration is via YAML files, environment variables, and dotenv files. Key entry points include `main.go` (application start), `cmd/cmd_root.go` (CLI root command), and `lego/client.go` (library entry point). The primary data flow involves the user specifying domains and challenge type, the client interacting with the ACME CA to create orders and solve challenges (e.g., creating a DNS TXT record via a provider API), and finally downloading and storing the issued certificate. External dependencies include the ACME CA servers, the DNS provider APIs, and optionally an HTTP server for HTTP-01 challenges. The codebase demonstrates strong engineering practices with extensive unit and end-to-end testing, a consistent provider interface, and several well-designed internal utilities (HTTP mock server, retry/polling, error wrappers). However, the large number of DNS providers introduces boilerplate duplication and potential API drift, and the project uses a custom Go-like language dialect that may pose tooling and onboarding risks.
The LLM identified 5 files worth highlighting for reuse:
Provides a chainable builder for constructing mock HTTP servers in tests. Allows declarative setup of request validation (headers, query parameters, form data, JSON body) and fixture-based responses. This pattern is self-contained and can be extracted to any Go project needing HTTP client testing without external mocking libraries.
Implements JWS (JSON Web Signature) signing for ACME protocol requests, including support for External Account Binding (EAB) and key rollover. Encapsulates the cryptographic operations (RSA/ECDSA signing, JWK thumbprint computation) in a clean interface. This component is reusable in any ACME client or JWS-based authentication system.
Provides generic retry and polling utilities with configurable backoff strategies (exponential, fixed) and timeout handling. Used extensively for DNS propagation checks and ACME challenge polling. The implementation is self-contained and can be extracted as a standalone Go library for any retry/polling scenario.
Reads TOML descriptor files for DNS providers and generates Go source code for the provider registry (`zz_gen_dns_providers.go`). This metaprogramming approach reduces boilerplate and ensures consistency across 200+ provider integrations. The pattern of generating code from declarative descriptors is reusable for any plugin-style architecture.
Implements a caching layer for DNS SOA (Start of Authority) lookups used to discover the authoritative zone for a domain. The cache reduces redundant DNS queries during challenge solving. This component is self-contained and can be reused in any Go application that needs efficient DNS zone discovery with TTL-based caching.