Add support for identity authentication.

ca/client.go

@@ -27,6 +27,7 @@ import (
 	"github.com/smallstep/certificates/authority/provisioner"
 	"github.com/smallstep/cli/config"
 	"github.com/smallstep/cli/crypto/x509util"
+	"golang.org/x/net/http2"
 	"gopkg.in/square/go-jose.v2/jwt"
 )
 
@@ -38,9 +39,13 @@ type clientOptions struct {
 	rootSHA256   string
 	rootFilename string
 	rootBundle   []byte
+	certificate  tls.Certificate
 }
 
 func (o *clientOptions) apply(opts []ClientOption) (err error) {
+	if err = o.applyDefaultIdentity(); err != nil {
+		return
+	}
 	for _, fn := range opts {
 		if err = fn(o); err != nil {
 			return
@@ -49,6 +54,32 @@ func (o *clientOptions) apply(opts []ClientOption) (err error) {
 	return
 }
 
+// applyDefaultIdentity sets the options for the default identity if the
+// identity file is present. The identity is enabled by default.
+func (o *clientOptions) applyDefaultIdentity() error {
+	b, err := ioutil.ReadFile(IdentityFile)
+	if err != nil {
+		return nil
+	}
+	var identity Identity
+	if err := json.Unmarshal(b, &identity); err != nil {
+		return errors.Wrapf(err, "error unmarshaling %s", IdentityFile)
+	}
+	if err := identity.Validate(); err != nil {
+		return err
+	}
+	opts, err := identity.Options()
+	if err != nil {
+		return err
+	}
+	for _, fn := range opts {
+		if err := fn(o); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
 // checkTransport checks if other ways to set up a transport have been provided.
 // If they have it returns an error.
 func (o *clientOptions) checkTransport() error {
@@ -85,10 +116,28 @@ func (o *clientOptions) getTransport(endpoint string) (tr http.RoundTripper, err
 			if tr, err = getTransportFromFile(rootFile); err != nil {
 				return nil, err
 			}
-			return tr, nil
 		}
-		return nil, errors.New("a transport, a root cert, or a root sha256 must be used")
+		if tr == nil {
+			return nil, errors.New("a transport, a root cert, or a root sha256 must be used")
+		}
+	}
+
+	// Add client certificate if available
+	if o.certificate.Certificate != nil {
+		switch tr := tr.(type) {
+		case *http.Transport:
+			if len(tr.TLSClientConfig.Certificates) == 0 && tr.TLSClientConfig.GetClientCertificate == nil {
+				tr.TLSClientConfig.Certificates = []tls.Certificate{o.certificate}
+			}
+		case *http2.Transport:
+			if len(tr.TLSClientConfig.Certificates) == 0 && tr.TLSClientConfig.GetClientCertificate == nil {
+				tr.TLSClientConfig.Certificates = []tls.Certificate{o.certificate}
+			}
+		default:
+			return nil, errors.Errorf("unsupported transport type %T", tr)
+		}
 	}
+
 	return tr, nil
 }
 
@@ -141,6 +190,15 @@ func WithCABundle(bundle []byte) ClientOption {
 	}
 }
 
+// WithCertificate will set the given certificate as the TLS client certificate
+// in the client.
+func WithCertificate(crt tls.Certificate) ClientOption {
+	return func(o *clientOptions) error {
+		o.certificate = crt
+		return nil
+	}
+}
+
 func getTransportFromFile(filename string) (http.RoundTripper, error) {
 	data, err := ioutil.ReadFile(filename)
 	if err != nil {

ca/identity.go

@@ -0,0 +1,69 @@
+package ca
+
+import (
+	"crypto/tls"
+	"path/filepath"
+	"strings"
+
+	"github.com/pkg/errors"
+	"github.com/smallstep/cli/config"
+)
+
+// IdentityType represents the different types of identity files.
+type IdentityType string
+
+// MutualTLS represents the identity using mTLS
+const MutualTLS IdentityType = "mTLS"
+
+// IdentityFile contains the location of the identity file.
+var IdentityFile = filepath.Join(config.StepPath(), "config", "identity.json")
+
+// Identity represents the identity file that can be used to authenticate with
+// the CA.
+type Identity struct {
+	Type        string `json:"type"`
+	Certificate string `json:"crt"`
+	Key         string `json:"key"`
+}
+
+// Kind returns the type for the given identity.
+func (i *Identity) Kind() IdentityType {
+	switch strings.ToLower(i.Type) {
+	case "mtls":
+		return MutualTLS
+	default:
+		return IdentityType(i.Type)
+	}
+}
+
+// Validate validates the identity object.
+func (i *Identity) Validate() error {
+	switch i.Kind() {
+	case MutualTLS:
+		if i.Certificate == "" {
+			return errors.New("identity.crt cannot be empty")
+		}
+		if i.Key == "" {
+			return errors.New("identity.key cannot be empty")
+		}
+		return nil
+	case "":
+		return errors.New("identity.type cannot be empty")
+	default:
+		return errors.Errorf("unsupported identity type %s", i.Type)
+	}
+}
+
+// Options returns the ClientOptions used for the given identity.
+func (i *Identity) Options() ([]ClientOption, error) {
+	switch i.Kind() {
+	case MutualTLS:
+		crt, err := tls.LoadX509KeyPair(i.Certificate, i.Key)
+		if err != nil {
+			return nil, errors.Wrap(err, "error creating identity certificate")
+		}
+		return []ClientOption{WithCertificate(crt)}, nil
+	default:
+		return nil, errors.Errorf("unsupported identity type %s", i.Type)
+	}
+}