automation.go

// Copyright 2015 Matthew Holt and The Caddy Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package caddytls

import (
	"encoding/json"
	"fmt"
	"net/http"
	"time"

	"github.com/caddyserver/caddy/v2"
	"github.com/caddyserver/certmagic"
	"github.com/go-acme/lego/v3/challenge"
	"go.uber.org/zap"
)

// AutomationConfig designates configuration for the
// construction and use of ACME clients.
type AutomationConfig struct {
	// The list of automation policies. The first matching
	// policy will be applied for a given certificate/name.
	Policies []*AutomationPolicy `json:"policies,omitempty"`

	// On-Demand TLS defers certificate operations to the
	// moment they are needed, e.g. during a TLS handshake.
	// Useful when you don't know all the hostnames at
	// config-time, or when you are not in control of the
	// domain names you are managing certificates for.
	// In 2015, Caddy became the first web server to
	// implement this experimental technology.
	//
	// Note that this field does not enable on-demand TLS,
	// it only configures it for when it is used. To enable
	// it, create an automation policy with `on_demand`.
	OnDemand *OnDemandConfig `json:"on_demand,omitempty"`

	// Caddy staples OCSP (and caches the response) for all
	// qualifying certificates by default. This setting
	// changes how often it scans responses for freshness,
	// and updates them if they are getting stale. Default: 1h
	OCSPCheckInterval caddy.Duration `json:"ocsp_interval,omitempty"`

	// Every so often, Caddy will scan all loaded, managed
	// certificates for expiration. This setting changes how
	// frequently the scan for expiring certificates is
	// performed. Default: 10m
	RenewCheckInterval caddy.Duration `json:"renew_interval,omitempty"`

	defaultPublicAutomationPolicy   *AutomationPolicy
	defaultInternalAutomationPolicy *AutomationPolicy // only initialized if necessary
}

// AutomationPolicy designates the policy for automating the
// management (obtaining, renewal, and revocation) of managed
// TLS certificates.
//
// An AutomationPolicy value is not valid until it has been
// provisioned; use the `AddAutomationPolicy()` method on the
// TLS app to properly provision a new policy.
type AutomationPolicy struct {
	// Which subjects (hostnames or IP addresses) this policy applies to.
	Subjects []string `json:"subjects,omitempty"`

	// The module that will issue certificates. Default: internal if all
	// subjects do not qualify for public certificates; othewise acme.
	IssuerRaw json.RawMessage `json:"issuer,omitempty" caddy:"namespace=tls.issuance inline_key=module"`

	// If true, certificates will be requested with MustStaple. Not all
	// CAs support this, and there are potentially serious consequences
	// of enabling this feature without proper threat modeling.
	MustStaple bool `json:"must_staple,omitempty"`

	// How long before a certificate's expiration to try renewing it,
	// as a function of its total lifetime. As a general and conservative
	// rule, it is a good idea to renew a certificate when it has about
	// 1/3 of its total lifetime remaining. This utilizes the majority
	// of the certificate's lifetime while still saving time to
	// troubleshoot problems. However, for extremely short-lived certs,
	// you may wish to increase the ratio to ~1/2.
	RenewalWindowRatio float64 `json:"renewal_window_ratio,omitempty"`

	// The type of key to generate for certificates.
	// Supported values: `ed25519`, `p256`, `p384`, `rsa2048`, `rsa4096`.
	KeyType string `json:"key_type,omitempty"`

	// Optionally configure a separate storage module associated with this
	// manager, instead of using Caddy's global/default-configured storage.
	StorageRaw json.RawMessage `json:"storage,omitempty" caddy:"namespace=caddy.storage inline_key=module"`

	// If true, certificates will be managed "on demand"; that is, during
	// TLS handshakes or when needed, as opposed to at startup or config
	// load.
	OnDemand bool `json:"on_demand,omitempty"`

	// Issuer stores the decoded issuer parameters. This is only
	// used to populate an underlying certmagic.Config's Issuer
	// field; it is not referenced thereafter.
	Issuer certmagic.Issuer `json:"-"`

	magic   *certmagic.Config
	storage certmagic.Storage
}

// Provision sets up ap and builds its underlying CertMagic config.
func (ap *AutomationPolicy) Provision(tlsApp *TLS) error {
	// policy-specific storage implementation
	if ap.StorageRaw != nil {
		val, err := tlsApp.ctx.LoadModule(ap, "StorageRaw")
		if err != nil {
			return fmt.Errorf("loading TLS storage module: %v", err)
		}
		cmStorage, err := val.(caddy.StorageConverter).CertMagicStorage()
		if err != nil {
			return fmt.Errorf("creating TLS storage configuration: %v", err)
		}
		ap.storage = cmStorage
	}

	var ond *certmagic.OnDemandConfig
	if ap.OnDemand {
		ond = &certmagic.OnDemandConfig{
			DecisionFunc: func(name string) error {
				// if an "ask" endpoint was defined, consult it first
				if tlsApp.Automation != nil &&
					tlsApp.Automation.OnDemand != nil &&
					tlsApp.Automation.OnDemand.Ask != "" {
					err := onDemandAskRequest(tlsApp.Automation.OnDemand.Ask, name)
					if err != nil {
						return err
					}
				}
				// check the rate limiter last because
				// doing so makes a reservation
				if !onDemandRateLimiter.Allow() {
					return fmt.Errorf("on-demand rate limit exceeded")
				}
				return nil
			},
		}
	}

	// if this automation policy has no Issuer defined, and
	// none of the subjects qualify for a public certificate,
	// set the issuer to internal so that these names can all
	// get certificates; critically, we can only do this if an
	// issuer is not explicitly configured (IssuerRaw, vs. just
	// Issuer) AND if the list of subjects is non-empty
	if ap.IssuerRaw == nil && len(ap.Subjects) > 0 {
		var anyPublic bool
		for _, s := range ap.Subjects {
			if certmagic.SubjectQualifiesForPublicCert(s) {
				anyPublic = true
				break
			}
		}
		if !anyPublic {
			tlsApp.logger.Info("setting internal issuer for automation policy that has only internal subjects but no issuer configured",
				zap.Strings("subjects", ap.Subjects))
			ap.IssuerRaw = json.RawMessage(`{"module":"internal"}`)
		}
	}

	// load and provision any explicitly-configured issuer module
	if ap.IssuerRaw != nil {
		val, err := tlsApp.ctx.LoadModule(ap, "IssuerRaw")
		if err != nil {
			return fmt.Errorf("loading TLS automation management module: %s", err)
		}
		ap.Issuer = val.(certmagic.Issuer)
	}

	keyType := ap.KeyType
	if keyType != "" {
		var err error
		keyType, err = caddy.NewReplacer().ReplaceOrErr(ap.KeyType, true, true)
		if err != nil {
			return fmt.Errorf("invalid key type %s: %s", ap.KeyType, err)
		}
		if _, ok := supportedCertKeyTypes[keyType]; !ok {
			return fmt.Errorf("unrecognized key type: %s", keyType)
		}
	}
	keySource := certmagic.StandardKeyGenerator{
		KeyType: supportedCertKeyTypes[keyType],
	}

	storage := ap.storage
	if storage == nil {
		storage = tlsApp.ctx.Storage()
	}

	template := certmagic.Config{
		MustStaple:         ap.MustStaple,
		RenewalWindowRatio: ap.RenewalWindowRatio,
		KeySource:          keySource,
		OnDemand:           ond,
		Storage:            storage,
		Issuer:             ap.Issuer, // if nil, certmagic.New() will create one
	}
	if rev, ok := ap.Issuer.(certmagic.Revoker); ok {
		template.Revoker = rev
	}
	ap.magic = certmagic.New(tlsApp.certCache, template)

	// sometimes issuers may need the parent certmagic.Config in
	// order to function properly (for example, ACMEIssuer needs
	// access to the correct storage and cache so it can solve
	// ACME challenges -- it's an annoying, inelegant circular
	// dependency that I don't know how to resolve nicely!)
	if annoying, ok := ap.Issuer.(ConfigSetter); ok {
		annoying.SetConfig(ap.magic)
	}

	return nil
}

// ChallengesConfig configures the ACME challenges.
type ChallengesConfig struct {
	// HTTP configures the ACME HTTP challenge. This
	// challenge is enabled and used automatically
	// and by default.
	HTTP *HTTPChallengeConfig `json:"http,omitempty"`

	// TLSALPN configures the ACME TLS-ALPN challenge.
	// This challenge is enabled and used automatically
	// and by default.
	TLSALPN *TLSALPNChallengeConfig `json:"tls-alpn,omitempty"`

	// Configures the ACME DNS challenge. Because this
	// challenge typically requires credentials for
	// interfacing with a DNS provider, this challenge is
	// not enabled by default. This is the only challenge
	// type which does not require a direct connection
	// to Caddy from an external server.
	// NOTE: DNS providers are currently being upgraded,
	// and this API is subject to change, but should be
	// stabilized soon.
	DNS *DNSChallengeConfig `json:"dns,omitempty"`

	// Optionally customize the host to which a listener
	// is bound if required for solving a challenge.
	BindHost string `json:"bind_host,omitempty"`
}

// HTTPChallengeConfig configures the ACME HTTP challenge.
type HTTPChallengeConfig struct {
	// If true, the HTTP challenge will be disabled.
	Disabled bool `json:"disabled,omitempty"`

	// An alternate port on which to service this
	// challenge. Note that the HTTP challenge port is
	// hard-coded into the spec and cannot be changed,
	// so you would have to forward packets from the
	// standard HTTP challenge port to this one.
	AlternatePort int `json:"alternate_port,omitempty"`
}

// TLSALPNChallengeConfig configures the ACME TLS-ALPN challenge.
type TLSALPNChallengeConfig struct {
	// If true, the TLS-ALPN challenge will be disabled.
	Disabled bool `json:"disabled,omitempty"`

	// An alternate port on which to service this
	// challenge. Note that the TLS-ALPN challenge port
	// is hard-coded into the spec and cannot be changed,
	// so you would have to forward packets from the
	// standard TLS-ALPN challenge port to this one.
	AlternatePort int `json:"alternate_port,omitempty"`
}

// DNSChallengeConfig configures the ACME DNS challenge.
// NOTE: This API is still experimental and is subject to change.
type DNSChallengeConfig struct {
	// The DNS provider module to use which will manage
	// the DNS records relevant to the ACME challenge.
	ProviderRaw json.RawMessage `json:"provider,omitempty" caddy:"namespace=dns.providers inline_key=name"`

	// The TTL of the TXT record used for the DNS challenge.
	TTL caddy.Duration `json:"ttl,omitempty"`

	provider challenge.Provider
}

// OnDemandConfig configures on-demand TLS, for obtaining
// needed certificates at handshake-time. Because this
// feature can easily be abused, you should use this to
// establish rate limits and/or an internal endpoint that
// Caddy can "ask" if it should be allowed to manage
// certificates for a given hostname.
type OnDemandConfig struct {
	// An optional rate limit to throttle the
	// issuance of certificates from handshakes.
	RateLimit *RateLimit `json:"rate_limit,omitempty"`

	// If Caddy needs to obtain or renew a certificate
	// during a TLS handshake, it will perform a quick
	// HTTP request to this URL to check if it should be
	// allowed to try to get a certificate for the name
	// in the "domain" query string parameter, like so:
	// `?domain=example.com`. The endpoint must return a
	// 200 OK status if a certificate is allowed;
	// anything else will cause it to be denied.
	// Redirects are not followed.
	Ask string `json:"ask,omitempty"`
}

// RateLimit specifies an interval with optional burst size.
type RateLimit struct {
	// A duration value. A certificate may be obtained 'burst'
	// times during this interval.
	Interval caddy.Duration `json:"interval,omitempty"`

	// How many times during an interval a certificate can be obtained.
	Burst int `json:"burst,omitempty"`
}

// ConfigSetter is implemented by certmagic.Issuers that
// need access to a parent certmagic.Config as part of
// their provisioning phase. For example, the ACMEIssuer
// requires a config so it can access storage and the
// cache to solve ACME challenges.
type ConfigSetter interface {
	SetConfig(cfg *certmagic.Config)
}

// These perpetual values are used for on-demand TLS.
var (
	onDemandRateLimiter = certmagic.NewRateLimiter(0, 0)
	onDemandAskClient   = &http.Client{
		Timeout: 10 * time.Second,
		CheckRedirect: func(req *http.Request, via []*http.Request) error {
			return fmt.Errorf("following http redirects is not allowed")
		},
	}
)