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azure.go
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azure.go
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package provisioner
import (
"context"
"crypto/sha256"
"crypto/x509"
"encoding/hex"
"encoding/json"
"io/ioutil"
"net/http"
"regexp"
"strings"
"time"
"github.com/pkg/errors"
"github.com/smallstep/cli/jose"
)
// azureOIDCBaseURL is the base discovery url for Microsoft Azure tokens.
const azureOIDCBaseURL = "https://login.microsoftonline.com"
// azureIdentityTokenURL is the URL to get the identity token for an instance.
const azureIdentityTokenURL = "http://169.254.169.254/metadata/identity/oauth2/token?api-version=2018-02-01&resource=https%3A%2F%2Fmanagement.azure.com%2F"
// azureDefaultAudience is the default audience used.
const azureDefaultAudience = "https://management.azure.com/"
// azureXMSMirIDRegExp is the regular expression used to parse the xms_mirid claim.
// Using case insensitive as resourceGroups appears as resourcegroups.
var azureXMSMirIDRegExp = regexp.MustCompile(`(?i)^/subscriptions/([^/]+)/resourceGroups/([^/]+)/providers/Microsoft.Compute/virtualMachines/([^/]+)$`)
type azureConfig struct {
oidcDiscoveryURL string
identityTokenURL string
}
func newAzureConfig(tenantID string) *azureConfig {
return &azureConfig{
oidcDiscoveryURL: azureOIDCBaseURL + "/" + tenantID + "/.well-known/openid-configuration",
identityTokenURL: azureIdentityTokenURL,
}
}
type azureIdentityToken struct {
AccessToken string `json:"access_token"`
RefreshToken string `json:"refresh_token"`
ClientID string `json:"client_id"`
ExpiresIn int64 `json:"expires_in,string"`
ExpiresOn int64 `json:"expires_on,string"`
ExtExpiresIn int64 `json:"ext_expires_in,string"`
NotBefore int64 `json:"not_before,string"`
Resource string `json:"resource"`
TokenType string `json:"token_type"`
}
type azurePayload struct {
jose.Claims
AppID string `json:"appid"`
AppIDAcr string `json:"appidacr"`
IdentityProvider string `json:"idp"`
ObjectID string `json:"oid"`
TenantID string `json:"tid"`
Version string `json:"ver"`
XMSMirID string `json:"xms_mirid"`
}
// Azure is the provisioner that supports identity tokens created from the
// Microsoft Azure Instance Metadata service.
//
// The default audience is "https://management.azure.com/".
//
// 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.
//
// Microsoft Azure identity docs are available at
// https://docs.microsoft.com/en-us/azure/active-directory/managed-identities-azure-resources/how-to-use-vm-token
// and https://docs.microsoft.com/en-us/azure/virtual-machines/windows/instance-metadata-service
type Azure struct {
Type string `json:"type"`
Name string `json:"name"`
TenantID string `json:"tenantId"`
ResourceGroups []string `json:"resourceGroups"`
Audience string `json:"audience,omitempty"`
DisableCustomSANs bool `json:"disableCustomSANs"`
DisableTrustOnFirstUse bool `json:"disableTrustOnFirstUse"`
Claims *Claims `json:"claims,omitempty"`
claimer *Claimer
config *azureConfig
oidcConfig openIDConfiguration
keyStore *keyStore
}
// GetID returns the provisioner unique identifier.
func (p *Azure) GetID() string {
return p.TenantID
}
// GetTokenID returns the identifier of the token. The default value for Azure
// the SHA256 of "xms_mirid", but if DisableTrustOnFirstUse is set to true, then
// it will be the token kid.
func (p *Azure) GetTokenID(token string) (string, error) {
jwt, err := jose.ParseSigned(token)
if err != nil {
return "", errors.Wrap(err, "error parsing token")
}
// Get claims w/out verification. We need to look up the provisioner
// key in order to verify the claims and we need the issuer from the claims
// before we can look up the provisioner.
var claims azurePayload
if err = jwt.UnsafeClaimsWithoutVerification(&claims); err != nil {
return "", errors.Wrap(err, "error verifying claims")
}
// If TOFU is disabled create return the token kid
if p.DisableTrustOnFirstUse {
return claims.ID, nil
}
sum := sha256.Sum256([]byte(claims.XMSMirID))
return strings.ToLower(hex.EncodeToString(sum[:])), nil
}
// GetName returns the name of the provisioner.
func (p *Azure) GetName() string {
return p.Name
}
// GetType returns the type of provisioner.
func (p *Azure) GetType() Type {
return TypeAzure
}
// GetEncryptedKey is not available in an Azure provisioner.
func (p *Azure) GetEncryptedKey() (kid string, key string, ok bool) {
return "", "", false
}
// GetIdentityToken retrieves from the metadata service the identity token and
// returns it.
func (p *Azure) GetIdentityToken(subject, caURL string) (string, error) {
// Initialize the config if this method is used from the cli.
p.assertConfig()
req, err := http.NewRequest("GET", p.config.identityTokenURL, http.NoBody)
if err != nil {
return "", errors.Wrap(err, "error creating request")
}
req.Header.Set("Metadata", "true")
resp, err := http.DefaultClient.Do(req)
if err != nil {
return "", errors.Wrap(err, "error getting identity token, are you in a Azure VM?")
}
defer resp.Body.Close()
b, err := ioutil.ReadAll(resp.Body)
if err != nil {
return "", errors.Wrap(err, "error reading identity token response")
}
if resp.StatusCode >= 400 {
return "", errors.Errorf("error getting identity token: status=%d, response=%s", resp.StatusCode, b)
}
var identityToken azureIdentityToken
if err := json.Unmarshal(b, &identityToken); err != nil {
return "", errors.Wrap(err, "error unmarshaling identity token response")
}
return identityToken.AccessToken, nil
}
// Init validates and initializes the Azure provisioner.
func (p *Azure) Init(config Config) (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.TenantID == "":
return errors.New("provisioner tenantId cannot be empty")
case p.Audience == "": // use default audience
p.Audience = azureDefaultAudience
}
// Initialize config
p.assertConfig()
// Update claims with global ones
if p.claimer, err = NewClaimer(p.Claims, config.Claims); err != nil {
return err
}
// Decode and validate openid-configuration endpoint
if err := getAndDecode(p.config.oidcDiscoveryURL, &p.oidcConfig); err != nil {
return err
}
if err := p.oidcConfig.Validate(); err != nil {
return errors.Wrapf(err, "error parsing %s", p.config.oidcDiscoveryURL)
}
// Get JWK key set
if p.keyStore, err = newKeyStore(p.oidcConfig.JWKSetURI); err != nil {
return err
}
return nil
}
// AuthorizeSign validates the given token and returns the sign options that
// will be used on certificate creation.
func (p *Azure) AuthorizeSign(ctx context.Context, token string) ([]SignOption, 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")
}
var found bool
var claims azurePayload
keys := p.keyStore.Get(jwt.Headers[0].KeyID)
for _, key := range keys {
if err := jwt.Claims(key.Public(), &claims); err == nil {
found = true
break
}
}
if !found {
return nil, errors.New("cannot validate token")
}
if err := claims.ValidateWithLeeway(jose.Expected{
Audience: []string{p.Audience},
Issuer: p.oidcConfig.Issuer,
Time: time.Now(),
}, 1*time.Minute); err != nil {
return nil, errors.Wrap(err, "failed to validate payload")
}
// Validate TenantID
if claims.TenantID != p.TenantID {
return nil, errors.New("validation failed: invalid tenant id claim (tid)")
}
re := azureXMSMirIDRegExp.FindStringSubmatch(claims.XMSMirID)
if len(re) != 4 {
return nil, errors.Errorf("error parsing xms_mirid claim: %s", claims.XMSMirID)
}
group, name := re[2], re[3]
// Filter by resource group
if len(p.ResourceGroups) > 0 {
var found bool
for _, g := range p.ResourceGroups {
if g == group {
found = true
break
}
}
if !found {
return nil, errors.New("validation failed: invalid resource group")
}
}
// Check for the sign ssh method, default to sign X.509
if m := MethodFromContext(ctx); m == SignSSHMethod {
if p.claimer.IsSSHCAEnabled() == false {
return nil, errors.Errorf("ssh ca is disabled for provisioner %s", p.GetID())
}
return p.authorizeSSHSign(claims, name)
}
// Enforce known common name and default DNS if configured.
// By default 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 {
// name will work only inside the virtual network
so = append(so, commonNameValidator(name))
so = append(so, dnsNamesValidator([]string{name}))
}
return append(so,
defaultPublicKeyValidator{},
profileDefaultDuration(p.claimer.DefaultTLSCertDuration()),
newProvisionerExtensionOption(TypeAzure, p.Name, p.TenantID),
newValidityValidator(p.claimer.MinTLSCertDuration(), p.claimer.MaxTLSCertDuration()),
), nil
}
// AuthorizeRenewal returns an error if the renewal is disabled.
func (p *Azure) AuthorizeRenewal(cert *x509.Certificate) error {
if p.claimer.IsDisableRenewal() {
return errors.Errorf("renew is disabled for provisioner %s", p.GetID())
}
return nil
}
// AuthorizeRevoke returns an error because revoke is not supported on Azure
// provisioners.
func (p *Azure) AuthorizeRevoke(token string) error {
return errors.New("revoke is not supported on a Azure provisioner")
}
// authorizeSSHSign returns the list of SignOption for a SignSSH request.
func (p *Azure) authorizeSSHSign(claims azurePayload, name string) ([]SignOption, error) {
signOptions := []SignOption{
// set the key id to the token subject
sshCertificateKeyIDModifier(name),
}
// Default to host + known hostnames
defaults := SSHOptions{
CertType: SSHHostCert,
Principals: []string{name},
}
// Validate user options
signOptions = append(signOptions, sshCertificateOptionsValidator(defaults))
// Set defaults if not given as user options
signOptions = append(signOptions, sshCertificateDefaultsModifier(defaults))
return append(signOptions,
// set the default extensions
&sshDefaultExtensionModifier{},
// checks the validity bounds, and set the validity if has not been set
&sshCertificateValidityModifier{p.claimer},
// validate public key
&sshDefaultPublicKeyValidator{},
// require all the fields in the SSH certificate
&sshCertificateDefaultValidator{},
), nil
}
// assertConfig initializes the config if it has not been initialized
func (p *Azure) assertConfig() {
if p.config == nil {
p.config = newAzureConfig(p.TenantID)
}
}