certificates/authority/provisioner/gcp.go

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package provisioner
import (
"bytes"
"context"
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"crypto/sha256"
"crypto/x509"
"encoding/hex"
"fmt"
"io/ioutil"
"net/http"
"net/url"
"strings"
"time"
"github.com/pkg/errors"
"github.com/smallstep/cli/jose"
)
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// gcpCertsURL is the url that serves Google OAuth2 public keys.
const gcpCertsURL = "https://www.googleapis.com/oauth2/v3/certs"
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// gcpIdentityURL is the base url for the identity document in GCP.
const gcpIdentityURL = "http://metadata/computeMetadata/v1/instance/service-accounts/default/identity"
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// gcpPayload extends jwt.Claims with custom GCP attributes.
type gcpPayload struct {
jose.Claims
AuthorizedParty string `json:"azp"`
Email string `json:"email"`
EmailVerified bool `json:"email_verified"`
Google gcpGooglePayload `json:"google"`
}
type gcpGooglePayload struct {
ComputeEngine gcpComputeEnginePayload `json:"compute_engine"`
}
type gcpComputeEnginePayload struct {
InstanceID string `json:"instance_id"`
InstanceName string `json:"instance_name"`
InstanceCreationTimestamp *jose.NumericDate `json:"instance_creation_timestamp"`
ProjectID string `json:"project_id"`
ProjectNumber int64 `json:"project_number"`
Zone string `json:"zone"`
LicenseID []string `json:"license_id"`
}
type gcpConfig struct {
CertsURL string
IdentityURL string
}
func newGCPConfig() *gcpConfig {
return &gcpConfig{
CertsURL: gcpCertsURL,
IdentityURL: gcpIdentityURL,
}
}
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// GCP is the provisioner that supports identity tokens created by the Google
// Cloud Platform metadata API.
//
// If DisableCustomSANs is true, only the internal DNS and IP will be added as a
// SAN. By default it will accept any SAN in the CSR.
//
// If DisableTrustOnFirstUse is true, multiple sign request for this provisioner
// with the same instance will be accepted. By default only the first request
// will be accepted.
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//
// If InstanceAge is set, only the instances with an instance_creation_timestamp
// within the given period will be accepted.
//
// Google Identity docs are available at
// https://cloud.google.com/compute/docs/instances/verifying-instance-identity
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type GCP struct {
Type string `json:"type"`
Name string `json:"name"`
ServiceAccounts []string `json:"serviceAccounts"`
ProjectIDs []string `json:"projectIDs"`
DisableCustomSANs bool `json:"disableCustomSANs"`
DisableTrustOnFirstUse bool `json:"disableTrustOnFirstUse"`
InstanceAge Duration `json:"instanceAge,omitempty"`
Claims *Claims `json:"claims,omitempty"`
claimer *Claimer
config *gcpConfig
keyStore *keyStore
audiences Audiences
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}
// GetID returns the provisioner unique identifier. The name should uniquely
// identify any GCP provisioner.
func (p *GCP) GetID() string {
return "gcp/" + p.Name
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}
// GetTokenID returns the identifier of the token. The default value for GCP the
// SHA256 of "provisioner_id.instance_id", but if DisableTrustOnFirstUse is set
// to true, then it will be the SHA256 of the token.
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func (p *GCP) GetTokenID(token string) (string, error) {
jwt, err := jose.ParseSigned(token)
if err != nil {
return "", errors.Wrap(err, "error parsing token")
}
// If TOFU is disabled create an ID for the token, so it cannot be reused.
if p.DisableTrustOnFirstUse {
sum := sha256.Sum256([]byte(token))
return strings.ToLower(hex.EncodeToString(sum[:])), nil
}
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// Get claims w/out verification.
var claims gcpPayload
if err = jwt.UnsafeClaimsWithoutVerification(&claims); err != nil {
return "", errors.Wrap(err, "error verifying claims")
}
// Create unique ID for Trust On First Use (TOFU). Only the first instance
// per provisioner is allowed as we don't have a way to trust the given
// sans.
unique := fmt.Sprintf("%s.%s", p.GetID(), claims.Google.ComputeEngine.InstanceID)
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sum := sha256.Sum256([]byte(unique))
return strings.ToLower(hex.EncodeToString(sum[:])), nil
}
// GetName returns the name of the provisioner.
func (p *GCP) GetName() string {
return p.Name
}
// GetType returns the type of provisioner.
func (p *GCP) GetType() Type {
return TypeGCP
}
// GetEncryptedKey is not available in a GCP provisioner.
func (p *GCP) GetEncryptedKey() (kid string, key string, ok bool) {
return "", "", false
}
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// GetIdentityURL returns the url that generates the GCP token.
func (p *GCP) GetIdentityURL(audience string) string {
// Initialize config if required
p.assertConfig()
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q := url.Values{}
q.Add("audience", audience)
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q.Add("format", "full")
q.Add("licenses", "FALSE")
return fmt.Sprintf("%s?%s", p.config.IdentityURL, q.Encode())
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}
// GetIdentityToken does an HTTP request to the identity url.
func (p *GCP) GetIdentityToken(subject, caURL string) (string, error) {
audience, err := generateSignAudience(caURL, p.GetID())
if err != nil {
return "", err
}
req, err := http.NewRequest("GET", p.GetIdentityURL(audience), http.NoBody)
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if err != nil {
return "", errors.Wrap(err, "error creating identity request")
}
req.Header.Set("Metadata-Flavor", "Google")
resp, err := http.DefaultClient.Do(req)
if err != nil {
return "", errors.Wrap(err, "error doing identity request, are you in a GCP VM?")
}
defer resp.Body.Close()
b, err := ioutil.ReadAll(resp.Body)
if err != nil {
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return "", errors.Wrap(err, "error on identity request")
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}
if resp.StatusCode >= 400 {
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return "", errors.Errorf("error on identity request: status=%d, response=%s", resp.StatusCode, b)
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}
return string(bytes.TrimSpace(b)), nil
}
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// Init validates and initializes the GCP provisioner.
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func (p *GCP) Init(config Config) error {
var err error
switch {
case p.Type == "":
return errors.New("provisioner type cannot be empty")
case p.Name == "":
return errors.New("provisioner name cannot be empty")
case p.InstanceAge.Value() < 0:
return errors.New("provisioner instanceAge cannot be negative")
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}
// Initialize config
p.assertConfig()
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// Update claims with global ones
if p.claimer, err = NewClaimer(p.Claims, config.Claims); err != nil {
return err
}
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// Initialize key store
p.keyStore, err = newKeyStore(p.config.CertsURL)
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if err != nil {
return err
}
p.audiences = config.Audiences.WithFragment(p.GetID())
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return nil
}
// AuthorizeSign validates the given token and returns the sign options that
// will be used on certificate creation.
func (p *GCP) AuthorizeSign(ctx context.Context, token string) ([]SignOption, error) {
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claims, err := p.authorizeToken(token)
if err != nil {
return nil, err
}
// Check for the sign ssh method, default to sign X.509
if m := MethodFromContext(ctx); m == SignSSHMethod {
return p.authorizeSSHSign(claims)
}
ce := claims.Google.ComputeEngine
// Enforce known common name and default DNS if configured.
// By default we we'll accept the CN and SANs in the CSR.
// There's no way to trust them other than TOFU.
var so []SignOption
if p.DisableCustomSANs {
dnsName1 := fmt.Sprintf("%s.c.%s.internal", ce.InstanceName, ce.ProjectID)
dnsName2 := fmt.Sprintf("%s.%s.c.%s.internal", ce.InstanceName, ce.Zone, ce.ProjectID)
so = append(so, commonNameSliceValidator([]string{
ce.InstanceName, ce.InstanceID, dnsName1, dnsName2,
}))
so = append(so, dnsNamesValidator([]string{
dnsName1, dnsName2,
}))
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}
return append(so,
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profileDefaultDuration(p.claimer.DefaultTLSCertDuration()),
newProvisionerExtensionOption(TypeGCP, p.Name, claims.Subject, "InstanceID", ce.InstanceID, "InstanceName", ce.InstanceName),
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newValidityValidator(p.claimer.MinTLSCertDuration(), p.claimer.MaxTLSCertDuration()),
), nil
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}
// AuthorizeRenewal returns an error if the renewal is disabled.
func (p *GCP) AuthorizeRenewal(cert *x509.Certificate) error {
if p.claimer.IsDisableRenewal() {
return errors.Errorf("renew is disabled for provisioner %s", p.GetID())
}
return nil
}
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// AuthorizeRevoke returns an error because revoke is not supported on GCP
// provisioners.
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func (p *GCP) AuthorizeRevoke(token string) error {
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return errors.New("revoke is not supported on a GCP provisioner")
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}
// assertConfig initializes the config if it has not been initialized.
func (p *GCP) assertConfig() {
if p.config == nil {
p.config = newGCPConfig()
}
}
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// authorizeToken performs common jwt authorization actions and returns the
// claims for case specific downstream parsing.
// e.g. a Sign request will auth/validate different fields than a Revoke request.
func (p *GCP) authorizeToken(token string) (*gcpPayload, error) {
jwt, err := jose.ParseSigned(token)
if err != nil {
return nil, errors.Wrapf(err, "error parsing token")
}
if len(jwt.Headers) == 0 {
return nil, errors.New("error parsing token: header is missing")
}
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var found bool
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var claims gcpPayload
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kid := jwt.Headers[0].KeyID
keys := p.keyStore.Get(kid)
for _, key := range keys {
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if err := jwt.Claims(key.Public(), &claims); err == nil {
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found = true
break
}
}
if !found {
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return nil, errors.Errorf("failed to validate payload: cannot find key for kid %s", kid)
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}
// According to "rfc7519 JSON Web Token" acceptable skew should be no
// more than a few minutes.
now := time.Now().UTC()
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if err = claims.ValidateWithLeeway(jose.Expected{
Issuer: "https://accounts.google.com",
Time: now,
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}, time.Minute); err != nil {
return nil, errors.Wrapf(err, "invalid token")
}
// validate audiences with the defaults
if !matchesAudience(claims.Audience, p.audiences.Sign) {
return nil, errors.New("invalid token: invalid audience claim (aud)")
}
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// validate subject (service account)
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if len(p.ServiceAccounts) > 0 {
var found bool
for _, sa := range p.ServiceAccounts {
if sa == claims.Subject || sa == claims.Email {
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found = true
break
}
}
if !found {
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return nil, errors.New("invalid token: invalid subject claim")
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}
}
// validate projects
if len(p.ProjectIDs) > 0 {
var found bool
for _, pi := range p.ProjectIDs {
if pi == claims.Google.ComputeEngine.ProjectID {
found = true
break
}
}
if !found {
return nil, errors.New("invalid token: invalid project id")
}
}
// validate instance age
if d := p.InstanceAge.Value(); d > 0 {
if now.Sub(claims.Google.ComputeEngine.InstanceCreationTimestamp.Time()) > d {
return nil, errors.New("token google.compute_engine.instance_creation_timestamp is too old")
}
}
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switch {
case claims.Google.ComputeEngine.InstanceID == "":
return nil, errors.New("token google.compute_engine.instance_id cannot be empty")
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case claims.Google.ComputeEngine.InstanceName == "":
return nil, errors.New("token google.compute_engine.instance_name cannot be empty")
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case claims.Google.ComputeEngine.ProjectID == "":
return nil, errors.New("token google.compute_engine.project_id cannot be empty")
case claims.Google.ComputeEngine.Zone == "":
return nil, errors.New("token google.compute_engine.zone cannot be empty")
}
return &claims, nil
}
// authorizeSSHSign returns the list of SignOption for a SignSSH request.
func (p *GCP) authorizeSSHSign(claims *gcpPayload) ([]SignOption, error) {
ce := claims.Google.ComputeEngine
signOptions := []SignOption{
// set the key id to the token subject
sshCertificateKeyIDModifier(ce.InstanceName),
}
signOptions = append(signOptions, &sshCertificateOptionsValidator{&SSHOptions{
CertType: SSHHostCert,
Principals: []string{
fmt.Sprintf("%s.c.%s.internal", ce.InstanceName, ce.ProjectID),
fmt.Sprintf("%s.%s.c.%s.internal", ce.InstanceName, ce.Zone, ce.ProjectID),
},
}})
return append(signOptions,
// set the default extensions
&sshDefaultExtensionModifier{},
// checks the validity bounds, and set the validity if has not been set
&sshCertificateValidityModifier{p.claimer},
// require all the fields in the SSH certificate
&sshCertificateDefaultValidator{},
), nil
}