package acme import ( "context" "crypto" "crypto/sha256" "crypto/subtle" "crypto/tls" "encoding/asn1" "encoding/base64" "encoding/hex" "encoding/json" "fmt" "io/ioutil" "net" "net/http" "net/url" "strings" "time" "go.step.sm/crypto/jose" ) // Challenge represents an ACME response Challenge type. type Challenge struct { ID string `json:"-"` AccountID string `json:"-"` AuthorizationID string `json:"-"` Value string `json:"-"` Type string `json:"type"` Status Status `json:"status"` Token string `json:"token"` ValidatedAt string `json:"validated,omitempty"` URL string `json:"url"` Error *Error `json:"error,omitempty"` } // ToLog enables response logging. func (ch *Challenge) ToLog() (interface{}, error) { b, err := json.Marshal(ch) if err != nil { return nil, WrapErrorISE(err, "error marshaling challenge for logging") } return string(b), nil } // Validate attempts to validate the challenge. Stores changes to the Challenge // type using the DB interface. // satisfactorily validated, the 'status' and 'validated' attributes are // updated. func (ch *Challenge) Validate(ctx context.Context, db DB, jwk *jose.JSONWebKey, vo *ValidateChallengeOptions) error { // If already valid or invalid then return without performing validation. if ch.Status != StatusPending { return nil } switch ch.Type { case "http-01": return http01Validate(ctx, ch, db, jwk, vo) case "dns-01": return dns01Validate(ctx, ch, db, jwk, vo) case "tls-alpn-01": return tlsalpn01Validate(ctx, ch, db, jwk, vo) default: return NewErrorISE("unexpected challenge type '%s'", ch.Type) } } func http01Validate(ctx context.Context, ch *Challenge, db DB, jwk *jose.JSONWebKey, vo *ValidateChallengeOptions) error { url := &url.URL{Scheme: "http", Host: ch.Value, Path: fmt.Sprintf("/.well-known/acme-challenge/%s", ch.Token)} resp, err := vo.HTTPGet(url.String()) if err != nil { return storeError(ctx, db, ch, false, WrapError(ErrorConnectionType, err, "error doing http GET for url %s", url)) } defer resp.Body.Close() if resp.StatusCode >= 400 { return storeError(ctx, db, ch, false, NewError(ErrorConnectionType, "error doing http GET for url %s with status code %d", url, resp.StatusCode)) } body, err := ioutil.ReadAll(resp.Body) if err != nil { return WrapErrorISE(err, "error reading "+ "response body for url %s", url) } keyAuth := strings.TrimSpace(string(body)) expected, err := KeyAuthorization(ch.Token, jwk) if err != nil { return err } if keyAuth != expected { return storeError(ctx, db, ch, true, NewError(ErrorRejectedIdentifierType, "keyAuthorization does not match; expected %s, but got %s", expected, keyAuth)) } // Update and store the challenge. ch.Status = StatusValid ch.Error = nil ch.ValidatedAt = clock.Now().Format(time.RFC3339) if err = db.UpdateChallenge(ctx, ch); err != nil { return WrapErrorISE(err, "error updating challenge") } return nil } func tlsalpn01Validate(ctx context.Context, ch *Challenge, db DB, jwk *jose.JSONWebKey, vo *ValidateChallengeOptions) error { config := &tls.Config{ NextProtos: []string{"acme-tls/1"}, // https://tools.ietf.org/html/rfc8737#section-4 // ACME servers that implement "acme-tls/1" MUST only negotiate TLS 1.2 // [RFC5246] or higher when connecting to clients for validation. MinVersion: tls.VersionTLS12, ServerName: ch.Value, InsecureSkipVerify: true, // we expect a self-signed challenge certificate } hostPort := net.JoinHostPort(ch.Value, "443") conn, err := vo.TLSDial("tcp", hostPort, config) if err != nil { return storeError(ctx, db, ch, false, WrapError(ErrorConnectionType, err, "error doing TLS dial for %s", hostPort)) } defer conn.Close() cs := conn.ConnectionState() certs := cs.PeerCertificates if len(certs) == 0 { return storeError(ctx, db, ch, true, NewError(ErrorRejectedIdentifierType, "%s challenge for %s resulted in no certificates", ch.Type, ch.Value)) } if !cs.NegotiatedProtocolIsMutual || cs.NegotiatedProtocol != "acme-tls/1" { return storeError(ctx, db, ch, true, NewError(ErrorRejectedIdentifierType, "cannot negotiate ALPN acme-tls/1 protocol for tls-alpn-01 challenge")) } leafCert := certs[0] if len(leafCert.DNSNames) != 1 || !strings.EqualFold(leafCert.DNSNames[0], ch.Value) { return storeError(ctx, db, ch, true, NewError(ErrorRejectedIdentifierType, "incorrect certificate for tls-alpn-01 challenge: leaf certificate must contain a single DNS name, %v", ch.Value)) } idPeAcmeIdentifier := asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 1, 31} idPeAcmeIdentifierV1Obsolete := asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 1, 30, 1} foundIDPeAcmeIdentifierV1Obsolete := false keyAuth, err := KeyAuthorization(ch.Token, jwk) if err != nil { return err } hashedKeyAuth := sha256.Sum256([]byte(keyAuth)) for _, ext := range leafCert.Extensions { if idPeAcmeIdentifier.Equal(ext.Id) { if !ext.Critical { return storeError(ctx, db, ch, true, NewError(ErrorRejectedIdentifierType, "incorrect certificate for tls-alpn-01 challenge: acmeValidationV1 extension not critical")) } var extValue []byte rest, err := asn1.Unmarshal(ext.Value, &extValue) if err != nil || len(rest) > 0 || len(hashedKeyAuth) != len(extValue) { return storeError(ctx, db, ch, true, NewError(ErrorRejectedIdentifierType, "incorrect certificate for tls-alpn-01 challenge: malformed acmeValidationV1 extension value")) } if subtle.ConstantTimeCompare(hashedKeyAuth[:], extValue) != 1 { return storeError(ctx, db, ch, true, NewError(ErrorRejectedIdentifierType, "incorrect certificate for tls-alpn-01 challenge: "+ "expected acmeValidationV1 extension value %s for this challenge but got %s", hex.EncodeToString(hashedKeyAuth[:]), hex.EncodeToString(extValue))) } ch.Status = StatusValid ch.Error = nil ch.ValidatedAt = clock.Now().Format(time.RFC3339) if err = db.UpdateChallenge(ctx, ch); err != nil { return WrapErrorISE(err, "tlsalpn01ValidateChallenge - error updating challenge") } return nil } if idPeAcmeIdentifierV1Obsolete.Equal(ext.Id) { foundIDPeAcmeIdentifierV1Obsolete = true } } if foundIDPeAcmeIdentifierV1Obsolete { return storeError(ctx, db, ch, true, NewError(ErrorRejectedIdentifierType, "incorrect certificate for tls-alpn-01 challenge: obsolete id-pe-acmeIdentifier in acmeValidationV1 extension")) } return storeError(ctx, db, ch, true, NewError(ErrorRejectedIdentifierType, "incorrect certificate for tls-alpn-01 challenge: missing acmeValidationV1 extension")) } func dns01Validate(ctx context.Context, ch *Challenge, db DB, jwk *jose.JSONWebKey, vo *ValidateChallengeOptions) error { // Normalize domain for wildcard DNS names // This is done to avoid making TXT lookups for domains like // _acme-challenge.*.example.com // Instead perform txt lookup for _acme-challenge.example.com domain := strings.TrimPrefix(ch.Value, "*.") txtRecords, err := vo.LookupTxt("_acme-challenge." + domain) if err != nil { return storeError(ctx, db, ch, false, WrapError(ErrorDNSType, err, "error looking up TXT records for domain %s", domain)) } expectedKeyAuth, err := KeyAuthorization(ch.Token, jwk) if err != nil { return err } h := sha256.Sum256([]byte(expectedKeyAuth)) expected := base64.RawURLEncoding.EncodeToString(h[:]) var found bool for _, r := range txtRecords { if r == expected { found = true break } } if !found { return storeError(ctx, db, ch, false, NewError(ErrorRejectedIdentifierType, "keyAuthorization does not match; expected %s, but got %s", expectedKeyAuth, txtRecords)) } // Update and store the challenge. ch.Status = StatusValid ch.Error = nil ch.ValidatedAt = clock.Now().Format(time.RFC3339) if err = db.UpdateChallenge(ctx, ch); err != nil { return WrapErrorISE(err, "error updating challenge") } return nil } // KeyAuthorization creates the ACME key authorization value from a token // and a jwk. func KeyAuthorization(token string, jwk *jose.JSONWebKey) (string, error) { thumbprint, err := jwk.Thumbprint(crypto.SHA256) if err != nil { return "", WrapErrorISE(err, "error generating JWK thumbprint") } encPrint := base64.RawURLEncoding.EncodeToString(thumbprint) return fmt.Sprintf("%s.%s", token, encPrint), nil } // storeError the given error to an ACME error and saves using the DB interface. func storeError(ctx context.Context, db DB, ch *Challenge, markInvalid bool, err *Error) error { ch.Error = err if markInvalid { ch.Status = StatusInvalid } if err := db.UpdateChallenge(ctx, ch); err != nil { return WrapErrorISE(err, "failure saving error to acme challenge") } return nil } type httpGetter func(string) (*http.Response, error) type lookupTxt func(string) ([]string, error) type tlsDialer func(network, addr string, config *tls.Config) (*tls.Conn, error) // ValidateChallengeOptions are ACME challenge validator functions. type ValidateChallengeOptions struct { HTTPGet httpGetter LookupTxt lookupTxt TLSDial tlsDialer }