package provisioner import ( "context" "crypto/sha256" "crypto/x509" "encoding/hex" "encoding/json" "io" "net/http" "regexp" "strings" "time" "github.com/pkg/errors" "github.com/smallstep/certificates/authority/policy" "github.com/smallstep/certificates/errs" "go.step.sm/crypto/jose" "go.step.sm/crypto/sshutil" "go.step.sm/crypto/x509util" ) // 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 { *base ID string `json:"-"` Type string `json:"type"` Name string `json:"name"` TenantID string `json:"tenantID"` ResourceGroups []string `json:"resourceGroups"` SubscriptionIDs []string `json:"subscriptionIDs"` ObjectIDs []string `json:"objectIDs"` Audience string `json:"audience,omitempty"` DisableCustomSANs bool `json:"disableCustomSANs"` DisableTrustOnFirstUse bool `json:"disableTrustOnFirstUse"` Claims *Claims `json:"claims,omitempty"` Options *Options `json:"options,omitempty"` claimer *Claimer config *azureConfig oidcConfig openIDConfiguration keyStore *keyStore x509Policy policy.X509Policy sshHostPolicy policy.HostPolicy } // GetID returns the provisioner unique identifier. func (p *Azure) 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 *Azure) GetIDForToken() 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 then allow token re-use. Azure caches the token for // 24h and without allowing the re-use we cannot use it twice. if p.DisableTrustOnFirstUse { return "", ErrAllowTokenReuse } 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, 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 := io.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 } // Initialize the x509 allow/deny policy engine if p.x509Policy, err = policy.NewX509PolicyEngine(p.Options.GetX509Options()); err != nil { return err } // Initialize the SSH allow/deny policy engine for host certificates if p.sshHostPolicy, err = policy.NewSSHHostPolicyEngine(p.Options.GetSSHOptions()); err != nil { return err } return nil } // authorizeToken returns the claims, name, group, subscription, identityObjectID, error. func (p *Azure) authorizeToken(token string) (*azurePayload, string, string, string, string, error) { jwt, err := jose.ParseSigned(token) if err != nil { return nil, "", "", "", "", errs.Wrap(http.StatusUnauthorized, err, "azure.authorizeToken; error parsing azure token") } if len(jwt.Headers) == 0 { return nil, "", "", "", "", errs.Unauthorized("azure.authorizeToken; azure token missing header") } 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, "", "", "", "", errs.Unauthorized("azure.authorizeToken; cannot validate azure 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, "", "", "", "", errs.Wrap(http.StatusUnauthorized, err, "azure.authorizeToken; failed to validate azure token payload") } // Validate TenantID if claims.TenantID != p.TenantID { return nil, "", "", "", "", errs.Unauthorized("azure.authorizeToken; azure token validation failed - invalid tenant id claim (tid)") } re := azureXMSMirIDRegExp.FindStringSubmatch(claims.XMSMirID) if len(re) != 4 { return nil, "", "", "", "", errs.Unauthorized("azure.authorizeToken; error parsing xms_mirid claim - %s", claims.XMSMirID) } identityObjectID := claims.ObjectID subscription, group, name := re[1], re[2], re[3] return &claims, name, group, subscription, identityObjectID, 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) { _, name, group, subscription, identityObjectID, err := p.authorizeToken(token) if err != nil { return nil, errs.Wrap(http.StatusInternalServerError, err, "azure.AuthorizeSign") } // 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, errs.Unauthorized("azure.AuthorizeSign; azure token validation failed - invalid resource group") } } // Filter by subscription id if len(p.SubscriptionIDs) > 0 { var found bool for _, s := range p.SubscriptionIDs { if s == subscription { found = true break } } if !found { return nil, errs.Unauthorized("azure.AuthorizeSign; azure token validation failed - invalid subscription id") } } // Filter by Azure AD identity object id if len(p.ObjectIDs) > 0 { var found bool for _, i := range p.ObjectIDs { if i == identityObjectID { found = true break } } if !found { return nil, errs.Unauthorized("azure.AuthorizeSign; azure token validation failed - invalid identity object id") } } // Template options data := x509util.NewTemplateData() data.SetCommonName(name) if v, err := unsafeParseSigned(token); err == nil { data.SetToken(v) } // 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), dnsNamesValidator([]string{name}), ipAddressesValidator(nil), emailAddressesValidator(nil), urisValidator(nil), ) // Enforce SANs in the template. data.SetSANs([]string{name}) } templateOptions, err := CustomTemplateOptions(p.Options, data, x509util.DefaultIIDLeafTemplate) if err != nil { return nil, errs.Wrap(http.StatusInternalServerError, err, "aws.AuthorizeSign") } return append(so, templateOptions, // modifiers / withOptions newProvisionerExtensionOption(TypeAzure, p.Name, p.TenantID), profileDefaultDuration(p.claimer.DefaultTLSCertDuration()), // validators defaultPublicKeyValidator{}, newValidityValidator(p.claimer.MinTLSCertDuration(), p.claimer.MaxTLSCertDuration()), newX509NamePolicyValidator(p.x509Policy), ), nil } // AuthorizeRenew returns an error if the renewal is disabled. // NOTE: This method does not actually validate the certificate or check it's // revocation status. Just confirms that the provisioner that created the // certificate was configured to allow renewals. func (p *Azure) AuthorizeRenew(ctx context.Context, cert *x509.Certificate) error { if p.claimer.IsDisableRenewal() { return errs.Unauthorized("azure.AuthorizeRenew; renew is disabled for azure provisioner '%s'", p.GetName()) } return nil } // AuthorizeSSHSign returns the list of SignOption for a SignSSH request. func (p *Azure) AuthorizeSSHSign(ctx context.Context, token string) ([]SignOption, error) { if !p.claimer.IsSSHCAEnabled() { return nil, errs.Unauthorized("azure.AuthorizeSSHSign; sshCA is disabled for provisioner '%s'", p.GetName()) } _, name, _, _, _, err := p.authorizeToken(token) if err != nil { return nil, errs.Wrap(http.StatusInternalServerError, err, "azure.AuthorizeSSHSign") } signOptions := []SignOption{} // Enforce host certificate. defaults := SignSSHOptions{ CertType: SSHHostCert, } // Validated principals. principals := []string{name} // 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, name, 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, "azure.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{}, // Ensure that all principal names are allowed newSSHNamePolicyValidator(p.sshHostPolicy, nil), ), nil } // assertConfig initializes the config if it has not been initialized func (p *Azure) assertConfig() { if p.config == nil { p.config = newAzureConfig(p.TenantID) } }