package provisioner import ( "bytes" "context" "crypto/sha256" "crypto/x509" "encoding/hex" "fmt" "io" "net/http" "net/url" "strings" "time" "github.com/pkg/errors" "github.com/smallstep/certificates/errs" "go.step.sm/crypto/jose" "go.step.sm/crypto/sshutil" "go.step.sm/crypto/x509util" ) // gcpCertsURL is the url that serves Google OAuth2 public keys. const gcpCertsURL = "https://www.googleapis.com/oauth2/v3/certs" // gcpIdentityURL is the base url for the identity document in GCP. const gcpIdentityURL = "http://metadata/computeMetadata/v1/instance/service-accounts/default/identity" // 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, } } // 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. // // 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 type GCP struct { *base ID string `json:"-"` 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"` Options *Options `json:"options,omitempty"` claimer *Claimer config *gcpConfig keyStore *keyStore audiences Audiences } // GetID returns the provisioner unique identifier. The name should uniquely // identify any GCP provisioner. func (p *GCP) GetID() string { if p.ID != "" { return p.ID } return p.GetIDForToken() } // GetIDForToken returns an identifier that will be used to load the provisioner // from a token. func (p *GCP) GetIDForToken() string { return "gcp/" + p.Name } // 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. 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 } // 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.GetIDForToken(), claims.Google.ComputeEngine.InstanceID) 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, key string, ok bool) { return "", "", false } // GetIdentityURL returns the url that generates the GCP token. func (p *GCP) GetIdentityURL(audience string) string { // Initialize config if required p.assertConfig() q := url.Values{} q.Add("audience", audience) q.Add("format", "full") q.Add("licenses", "FALSE") return fmt.Sprintf("%s?%s", p.config.IdentityURL, q.Encode()) } // GetIdentityToken does an HTTP request to the identity url. func (p *GCP) GetIdentityToken(subject, caURL string) (string, error) { audience, err := generateSignAudience(caURL, p.GetIDForToken()) if err != nil { return "", err } req, err := http.NewRequest("GET", p.GetIdentityURL(audience), http.NoBody) 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 := io.ReadAll(resp.Body) if err != nil { return "", errors.Wrap(err, "error on identity request") } if resp.StatusCode >= 400 { return "", errors.Errorf("error on identity request: status=%d, response=%s", resp.StatusCode, b) } return string(bytes.TrimSpace(b)), nil } // Init validates and initializes the GCP provisioner. 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") } // Initialize config p.assertConfig() // Update claims with global ones if p.claimer, err = NewClaimer(p.Claims, config.Claims); err != nil { return err } // Initialize key store p.keyStore, err = newKeyStore(p.config.CertsURL) if err != nil { return err } p.audiences = config.Audiences.WithFragment(p.GetIDForToken()) 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) { claims, err := p.authorizeToken(token) if err != nil { return nil, errs.Wrap(http.StatusInternalServerError, err, "gcp.AuthorizeSign") } ce := claims.Google.ComputeEngine // Template options data := x509util.NewTemplateData() data.SetCommonName(ce.InstanceName) if v, err := unsafeParseSigned(token); err == nil { data.SetToken(v) } // 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, }), dnsNamesValidator([]string{ dnsName1, dnsName2, }), ipAddressesValidator(nil), emailAddressesValidator(nil), urisValidator(nil), ) // Template SANs data.SetSANs([]string{dnsName1, dnsName2}) } templateOptions, err := CustomTemplateOptions(p.Options, data, x509util.DefaultIIDLeafTemplate) if err != nil { return nil, errs.Wrap(http.StatusInternalServerError, err, "gcp.AuthorizeSign") } return append(so, templateOptions, // modifiers / withOptions newProvisionerExtensionOption(TypeGCP, p.Name, claims.Subject, "InstanceID", ce.InstanceID, "InstanceName", ce.InstanceName), profileDefaultDuration(p.claimer.DefaultTLSCertDuration()), // validators defaultPublicKeyValidator{}, newValidityValidator(p.claimer.MinTLSCertDuration(), p.claimer.MaxTLSCertDuration()), ), nil } // AuthorizeRenew returns an error if the renewal is disabled. func (p *GCP) AuthorizeRenew(ctx context.Context, cert *x509.Certificate) error { if p.claimer.IsDisableRenewal() { return errs.Unauthorized("gcp.AuthorizeRenew; renew is disabled for gcp provisioner '%s'", p.GetName()) } return nil } // assertConfig initializes the config if it has not been initialized. func (p *GCP) assertConfig() { if p.config == nil { p.config = newGCPConfig() } } // 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, errs.Wrap(http.StatusUnauthorized, err, "gcp.authorizeToken; error parsing gcp token") } if len(jwt.Headers) == 0 { return nil, errs.Unauthorized("gcp.authorizeToken; error parsing gcp token - header is missing") } var found bool var claims gcpPayload kid := jwt.Headers[0].KeyID keys := p.keyStore.Get(kid) for _, key := range keys { if err := jwt.Claims(key.Public(), &claims); err == nil { found = true break } } if !found { return nil, errs.Unauthorized("gcp.authorizeToken; failed to validate gcp token payload - cannot find key for kid %s", kid) } // According to "rfc7519 JSON Web Token" acceptable skew should be no // more than a few minutes. now := time.Now().UTC() if err = claims.ValidateWithLeeway(jose.Expected{ Issuer: "https://accounts.google.com", Time: now, }, time.Minute); err != nil { return nil, errs.Wrap(http.StatusUnauthorized, err, "gcp.authorizeToken; invalid gcp token payload") } // validate audiences with the defaults if !matchesAudience(claims.Audience, p.audiences.Sign) { return nil, errs.Unauthorized("gcp.authorizeToken; invalid gcp token - invalid audience claim (aud)") } // validate subject (service account) if len(p.ServiceAccounts) > 0 { var found bool for _, sa := range p.ServiceAccounts { if sa == claims.Subject || sa == claims.Email { found = true break } } if !found { return nil, errs.Unauthorized("gcp.authorizeToken; invalid gcp token - invalid subject claim") } } // 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, errs.Unauthorized("gcp.authorizeToken; invalid gcp 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, errs.Unauthorized("gcp.authorizeToken; token google.compute_engine.instance_creation_timestamp is too old") } } switch { case claims.Google.ComputeEngine.InstanceID == "": return nil, errs.Unauthorized("gcp.authorizeToken; gcp token google.compute_engine.instance_id cannot be empty") case claims.Google.ComputeEngine.InstanceName == "": return nil, errs.Unauthorized("gcp.authorizeToken; gcp token google.compute_engine.instance_name cannot be empty") case claims.Google.ComputeEngine.ProjectID == "": return nil, errs.Unauthorized("gcp.authorizeToken; gcp token google.compute_engine.project_id cannot be empty") case claims.Google.ComputeEngine.Zone == "": return nil, errs.Unauthorized("gcp.authorizeToken; gcp 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(ctx context.Context, token string) ([]SignOption, error) { if !p.claimer.IsSSHCAEnabled() { return nil, errs.Unauthorized("gcp.AuthorizeSSHSign; sshCA is disabled for gcp provisioner '%s'", p.GetName()) } claims, err := p.authorizeToken(token) if err != nil { return nil, errs.Wrap(http.StatusInternalServerError, err, "gcp.AuthorizeSSHSign") } ce := claims.Google.ComputeEngine signOptions := []SignOption{} // Enforce host certificate. defaults := SignSSHOptions{ CertType: SSHHostCert, } // Validated principals. 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), } // Only enforce known principals if disable custom sans is true. if p.DisableCustomSANs { defaults.Principals = principals } else { // Check that at least one principal is sent in the request. signOptions = append(signOptions, &sshCertOptionsRequireValidator{ Principals: true, }) } // Certificate templates. data := sshutil.CreateTemplateData(sshutil.HostCert, ce.InstanceName, principals) if v, err := unsafeParseSigned(token); err == nil { data.SetToken(v) } templateOptions, err := CustomSSHTemplateOptions(p.Options, data, sshutil.DefaultIIDTemplate) if err != nil { return nil, errs.Wrap(http.StatusInternalServerError, err, "gcp.AuthorizeSSHSign") } signOptions = append(signOptions, templateOptions) return append(signOptions, // Validate user SignSSHOptions. sshCertOptionsValidator(defaults), // Set the validity bounds if not set. &sshDefaultDuration{p.claimer}, // Validate public key &sshDefaultPublicKeyValidator{}, // Validate the validity period. &sshCertValidityValidator{p.claimer}, // Require all the fields in the SSH certificate &sshCertDefaultValidator{}, ), nil }