mirror of
https://github.com/smallstep/certificates.git
synced 2024-11-17 15:29:21 +00:00
381 lines
12 KiB
Go
381 lines
12 KiB
Go
package acme
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import (
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"context"
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"crypto"
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"crypto/sha256"
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"crypto/subtle"
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"crypto/tls"
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"encoding/asn1"
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"encoding/base64"
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"encoding/hex"
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"encoding/json"
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"errors"
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"fmt"
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"io"
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"net"
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"net/url"
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"reflect"
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"strings"
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"time"
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"go.step.sm/crypto/jose"
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)
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type ChallengeType string
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const (
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// HTTP01 is the http-01 ACME challenge type
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HTTP01 ChallengeType = "http-01"
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// DNS01 is the dns-01 ACME challenge type
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DNS01 ChallengeType = "dns-01"
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// TLSALPN01 is the tls-alpn-01 ACME challenge type
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TLSALPN01 ChallengeType = "tls-alpn-01"
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)
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// Challenge represents an ACME response Challenge type.
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type Challenge struct {
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ID string `json:"-"`
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AccountID string `json:"-"`
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AuthorizationID string `json:"-"`
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Value string `json:"-"`
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Type ChallengeType `json:"type"`
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Status Status `json:"status"`
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Token string `json:"token"`
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ValidatedAt string `json:"validated,omitempty"`
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URL string `json:"url"`
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Error *Error `json:"error,omitempty"`
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}
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// ToLog enables response logging.
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func (ch *Challenge) ToLog() (interface{}, error) {
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b, err := json.Marshal(ch)
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if err != nil {
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return nil, WrapErrorISE(err, "error marshaling challenge for logging")
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}
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return string(b), nil
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}
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// Validate attempts to validate the challenge. Stores changes to the Challenge
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// type using the DB interface.
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// satisfactorily validated, the 'status' and 'validated' attributes are
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// updated.
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func (ch *Challenge) Validate(ctx context.Context, db DB, jwk *jose.JSONWebKey) error {
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// If already valid or invalid then return without performing validation.
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if ch.Status != StatusPending {
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return nil
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}
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switch ch.Type {
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case HTTP01:
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return http01Validate(ctx, ch, db, jwk)
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case DNS01:
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return dns01Validate(ctx, ch, db, jwk)
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case TLSALPN01:
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return tlsalpn01Validate(ctx, ch, db, jwk)
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default:
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return NewErrorISE("unexpected challenge type '%s'", ch.Type)
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}
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}
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func http01Validate(ctx context.Context, ch *Challenge, db DB, jwk *jose.JSONWebKey) error {
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u := &url.URL{Scheme: "http", Host: http01ChallengeHost(ch.Value), Path: fmt.Sprintf("/.well-known/acme-challenge/%s", ch.Token)}
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vc := MustClientFromContext(ctx)
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resp, err := vc.Get(u.String())
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if err != nil {
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return storeError(ctx, db, ch, false, WrapError(ErrorConnectionType, err,
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"error doing http GET for url %s", u))
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}
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defer resp.Body.Close()
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if resp.StatusCode >= 400 {
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return storeError(ctx, db, ch, false, NewError(ErrorConnectionType,
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"error doing http GET for url %s with status code %d", u, resp.StatusCode))
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}
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body, err := io.ReadAll(resp.Body)
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if err != nil {
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return WrapErrorISE(err, "error reading "+
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"response body for url %s", u)
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}
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keyAuth := strings.TrimSpace(string(body))
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expected, err := KeyAuthorization(ch.Token, jwk)
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if err != nil {
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return err
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}
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if keyAuth != expected {
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return storeError(ctx, db, ch, true, NewError(ErrorRejectedIdentifierType,
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"keyAuthorization does not match; expected %s, but got %s", expected, keyAuth))
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}
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// Update and store the challenge.
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ch.Status = StatusValid
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ch.Error = nil
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ch.ValidatedAt = clock.Now().Format(time.RFC3339)
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if err = db.UpdateChallenge(ctx, ch); err != nil {
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return WrapErrorISE(err, "error updating challenge")
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}
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return nil
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}
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// http01ChallengeHost checks if a Challenge value is an IPv6 address
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// and adds square brackets if that's the case, so that it can be used
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// as a hostname. Returns the original Challenge value as the host to
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// use in other cases.
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func http01ChallengeHost(value string) string {
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if ip := net.ParseIP(value); ip != nil && ip.To4() == nil {
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value = "[" + value + "]"
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}
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return value
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}
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func tlsAlert(err error) uint8 {
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var opErr *net.OpError
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if errors.As(err, &opErr) {
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v := reflect.ValueOf(opErr.Err)
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if v.Kind() == reflect.Uint8 {
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return uint8(v.Uint())
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}
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}
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return 0
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}
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func tlsalpn01Validate(ctx context.Context, ch *Challenge, db DB, jwk *jose.JSONWebKey) error {
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config := &tls.Config{
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NextProtos: []string{"acme-tls/1"},
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// https://tools.ietf.org/html/rfc8737#section-4
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// ACME servers that implement "acme-tls/1" MUST only negotiate TLS 1.2
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// [RFC5246] or higher when connecting to clients for validation.
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MinVersion: tls.VersionTLS12,
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ServerName: serverName(ch),
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InsecureSkipVerify: true, // nolint:gosec // we expect a self-signed challenge certificate
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}
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hostPort := net.JoinHostPort(ch.Value, "443")
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vc := MustClientFromContext(ctx)
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conn, err := vc.TLSDial("tcp", hostPort, config)
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if err != nil {
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// With Go 1.17+ tls.Dial fails if there's no overlap between configured
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// client and server protocols. When this happens the connection is
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// closed with the error no_application_protocol(120) as required by
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// RFC7301. See https://golang.org/doc/go1.17#ALPN
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if tlsAlert(err) == 120 {
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return storeError(ctx, db, ch, true, NewError(ErrorRejectedIdentifierType,
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"cannot negotiate ALPN acme-tls/1 protocol for tls-alpn-01 challenge"))
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}
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return storeError(ctx, db, ch, false, WrapError(ErrorConnectionType, err,
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"error doing TLS dial for %s", hostPort))
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}
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defer conn.Close()
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cs := conn.ConnectionState()
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certs := cs.PeerCertificates
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if len(certs) == 0 {
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return storeError(ctx, db, ch, true, NewError(ErrorRejectedIdentifierType,
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"%s challenge for %s resulted in no certificates", ch.Type, ch.Value))
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}
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if cs.NegotiatedProtocol != "acme-tls/1" {
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return storeError(ctx, db, ch, true, NewError(ErrorRejectedIdentifierType,
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"cannot negotiate ALPN acme-tls/1 protocol for tls-alpn-01 challenge"))
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}
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leafCert := certs[0]
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// if no DNS names present, look for IP address and verify that exactly one exists
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if len(leafCert.DNSNames) == 0 {
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if len(leafCert.IPAddresses) != 1 || !leafCert.IPAddresses[0].Equal(net.ParseIP(ch.Value)) {
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return storeError(ctx, db, ch, true, NewError(ErrorRejectedIdentifierType,
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"incorrect certificate for tls-alpn-01 challenge: leaf certificate must contain a single IP address or DNS name, %v", ch.Value))
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}
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} else {
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if len(leafCert.DNSNames) != 1 || !strings.EqualFold(leafCert.DNSNames[0], ch.Value) {
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return storeError(ctx, db, ch, true, NewError(ErrorRejectedIdentifierType,
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"incorrect certificate for tls-alpn-01 challenge: leaf certificate must contain a single IP address or DNS name, %v", ch.Value))
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}
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}
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idPeAcmeIdentifier := asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 1, 31}
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idPeAcmeIdentifierV1Obsolete := asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 1, 30, 1}
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foundIDPeAcmeIdentifierV1Obsolete := false
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keyAuth, err := KeyAuthorization(ch.Token, jwk)
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if err != nil {
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return err
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}
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hashedKeyAuth := sha256.Sum256([]byte(keyAuth))
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for _, ext := range leafCert.Extensions {
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if idPeAcmeIdentifier.Equal(ext.Id) {
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if !ext.Critical {
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return storeError(ctx, db, ch, true, NewError(ErrorRejectedIdentifierType,
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"incorrect certificate for tls-alpn-01 challenge: acmeValidationV1 extension not critical"))
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}
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var extValue []byte
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rest, err := asn1.Unmarshal(ext.Value, &extValue)
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if err != nil || len(rest) > 0 || len(hashedKeyAuth) != len(extValue) {
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return storeError(ctx, db, ch, true, NewError(ErrorRejectedIdentifierType,
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"incorrect certificate for tls-alpn-01 challenge: malformed acmeValidationV1 extension value"))
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}
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if subtle.ConstantTimeCompare(hashedKeyAuth[:], extValue) != 1 {
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return storeError(ctx, db, ch, true, NewError(ErrorRejectedIdentifierType,
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"incorrect certificate for tls-alpn-01 challenge: "+
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"expected acmeValidationV1 extension value %s for this challenge but got %s",
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hex.EncodeToString(hashedKeyAuth[:]), hex.EncodeToString(extValue)))
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}
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ch.Status = StatusValid
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ch.Error = nil
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ch.ValidatedAt = clock.Now().Format(time.RFC3339)
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if err = db.UpdateChallenge(ctx, ch); err != nil {
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return WrapErrorISE(err, "tlsalpn01ValidateChallenge - error updating challenge")
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}
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return nil
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}
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if idPeAcmeIdentifierV1Obsolete.Equal(ext.Id) {
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foundIDPeAcmeIdentifierV1Obsolete = true
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}
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}
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if foundIDPeAcmeIdentifierV1Obsolete {
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return storeError(ctx, db, ch, true, NewError(ErrorRejectedIdentifierType,
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"incorrect certificate for tls-alpn-01 challenge: obsolete id-pe-acmeIdentifier in acmeValidationV1 extension"))
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}
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return storeError(ctx, db, ch, true, NewError(ErrorRejectedIdentifierType,
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"incorrect certificate for tls-alpn-01 challenge: missing acmeValidationV1 extension"))
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}
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func dns01Validate(ctx context.Context, ch *Challenge, db DB, jwk *jose.JSONWebKey) error {
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// Normalize domain for wildcard DNS names
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// This is done to avoid making TXT lookups for domains like
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// _acme-challenge.*.example.com
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// Instead perform txt lookup for _acme-challenge.example.com
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domain := strings.TrimPrefix(ch.Value, "*.")
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vc := MustClientFromContext(ctx)
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txtRecords, err := vc.LookupTxt("_acme-challenge." + domain)
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if err != nil {
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return storeError(ctx, db, ch, false, WrapError(ErrorDNSType, err,
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"error looking up TXT records for domain %s", domain))
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}
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expectedKeyAuth, err := KeyAuthorization(ch.Token, jwk)
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if err != nil {
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return err
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}
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h := sha256.Sum256([]byte(expectedKeyAuth))
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expected := base64.RawURLEncoding.EncodeToString(h[:])
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var found bool
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for _, r := range txtRecords {
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if r == expected {
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found = true
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break
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}
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}
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if !found {
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return storeError(ctx, db, ch, false, NewError(ErrorRejectedIdentifierType,
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"keyAuthorization does not match; expected %s, but got %s", expectedKeyAuth, txtRecords))
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}
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// Update and store the challenge.
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ch.Status = StatusValid
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ch.Error = nil
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ch.ValidatedAt = clock.Now().Format(time.RFC3339)
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if err = db.UpdateChallenge(ctx, ch); err != nil {
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return WrapErrorISE(err, "error updating challenge")
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}
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return nil
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}
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// serverName determines the SNI HostName to set based on an acme.Challenge
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// for TLS-ALPN-01 challenges RFC8738 states that, if HostName is an IP, it
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// should be the ARPA address https://datatracker.ietf.org/doc/html/rfc8738#section-6.
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// It also references TLS Extensions [RFC6066].
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func serverName(ch *Challenge) string {
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var serverName string
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ip := net.ParseIP(ch.Value)
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if ip != nil {
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serverName = reverseAddr(ip)
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} else {
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serverName = ch.Value
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}
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return serverName
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}
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// reverseaddr returns the in-addr.arpa. or ip6.arpa. hostname of the IP
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// address addr suitable for rDNS (PTR) record lookup or an error if it fails
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// to parse the IP address.
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// Implementation taken and adapted from https://golang.org/src/net/dnsclient.go?s=780:834#L20
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func reverseAddr(ip net.IP) (arpa string) {
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if ip.To4() != nil {
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return uitoa(uint(ip[15])) + "." + uitoa(uint(ip[14])) + "." + uitoa(uint(ip[13])) + "." + uitoa(uint(ip[12])) + ".in-addr.arpa."
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}
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// Must be IPv6
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buf := make([]byte, 0, len(ip)*4+len("ip6.arpa."))
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// Add it, in reverse, to the buffer
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for i := len(ip) - 1; i >= 0; i-- {
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v := ip[i]
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buf = append(buf, hexit[v&0xF],
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'.',
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hexit[v>>4],
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'.')
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}
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// Append "ip6.arpa." and return (buf already has the final .)
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buf = append(buf, "ip6.arpa."...)
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return string(buf)
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}
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// Convert unsigned integer to decimal string.
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// Implementation taken from https://golang.org/src/net/parse.go
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func uitoa(val uint) string {
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if val == 0 { // avoid string allocation
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return "0"
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}
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var buf [20]byte // big enough for 64bit value base 10
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i := len(buf) - 1
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for val >= 10 {
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q := val / 10
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buf[i] = byte('0' + val - q*10)
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i--
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val = q
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}
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// val < 10
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buf[i] = byte('0' + val)
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return string(buf[i:])
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}
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const hexit = "0123456789abcdef"
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// KeyAuthorization creates the ACME key authorization value from a token
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// and a jwk.
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func KeyAuthorization(token string, jwk *jose.JSONWebKey) (string, error) {
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thumbprint, err := jwk.Thumbprint(crypto.SHA256)
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if err != nil {
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return "", WrapErrorISE(err, "error generating JWK thumbprint")
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}
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encPrint := base64.RawURLEncoding.EncodeToString(thumbprint)
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return fmt.Sprintf("%s.%s", token, encPrint), nil
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}
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// storeError the given error to an ACME error and saves using the DB interface.
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func storeError(ctx context.Context, db DB, ch *Challenge, markInvalid bool, err *Error) error {
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ch.Error = err
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if markInvalid {
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ch.Status = StatusInvalid
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}
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if err := db.UpdateChallenge(ctx, ch); err != nil {
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return WrapErrorISE(err, "failure saving error to acme challenge")
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}
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return nil
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}
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