Remove principals on OIDC and write identity in proxycommand.

command/ssh/login.go

@@ -197,6 +197,14 @@ func loginAction(ctx *cli.Context) error {
 		identityKey = key
 	}
 
+	// NOTE: For OIDC token the principals should be completely empty. The OIDC
+	// provisioner is responsible for setting default principals by using an
+	// identity function.
+	if email, ok := tokenHasEmail(token); ok {
+		principals = []string{}
+		subject = email
+	}
+
 	resp, err := caClient.SSHSign(&api.SSHSignRequest{
 		PublicKey:        sshPub.Marshal(),
 		OTT:              token,

command/ssh/proxycommand.go

@@ -1,6 +1,7 @@
 package ssh
 
 import (
+	"crypto"
 	"encoding/json"
 	"io"
 	"net"
@@ -13,6 +14,7 @@ import (
 	"github.com/pkg/errors"
 	"github.com/smallstep/certificates/api"
 	"github.com/smallstep/certificates/authority/provisioner"
+	"github.com/smallstep/certificates/ca"
 	"github.com/smallstep/cli/command"
 	"github.com/smallstep/cli/crypto/keys"
 	"github.com/smallstep/cli/crypto/sshutil"
@@ -146,11 +148,36 @@ func doLoginIfNeeded(ctx *cli.Context, subject string) error {
 		return err
 	}
 
+	// NOTE: For OIDC token the principals should be completely empty. The OIDC
+	// provisioner is responsible for setting default principals by using an
+	// identity function.
+	if email, ok := tokenHasEmail(token); ok {
+		principals = []string{}
+		subject = email
+	}
+
 	caClient, err := flow.GetClient(ctx, token)
 	if err != nil {
 		return err
 	}
 
+	version, err := caClient.Version()
+	if err != nil {
+		return err
+	}
+
+	// Generate identity certificate (x509) if necessary
+	var identityCSR api.CertificateRequest
+	var identityKey crypto.PrivateKey
+	if version.RequireClientAuthentication {
+		csr, key, err := ca.NewIdentityRequest(subject)
+		if err != nil {
+			return err
+		}
+		identityCSR = *csr
+		identityKey = key
+	}
+
 	// Generate keypair
 	pub, priv, err := keys.GenerateDefaultKeyPair()
 	if err != nil {
@@ -170,11 +197,19 @@ func doLoginIfNeeded(ctx *cli.Context, subject string) error {
 		CertType:    provisioner.SSHUserCert,
 		ValidAfter:  validAfter,
 		ValidBefore: validBefore,
+		IdentityCSR: identityCSR,
 	})
 	if err != nil {
 		return err
 	}
 
+	// Write x509 identity certificate
+	if version.RequireClientAuthentication {
+		if err := ca.WriteDefaultIdentity(resp.IdentityCertificate, identityKey); err != nil {
+			return err
+		}
+	}
+
 	// Add certificate and private key to agent
 	if err := agent.AddCertificate(subject, resp.Certificate.Certificate, priv); err != nil {
 		return err

command/ssh/ssh.go

@@ -194,3 +194,13 @@ func loginOnUnauthorized(ctx *cli.Context) (ca.RetryFunc, error) {
 		return true
 	}, nil
 }
+
+// tokenHasEmail returns if the token payload has an email address. This is
+// mainly used on OIDC token.
+func tokenHasEmail(s string) (string, bool) {
+	jwt, err := token.ParseInsecure(s)
+	if err != nil {
+		return "", false
+	}
+	return jwt.Payload.Email, jwt.Payload.Email != ""
+}