diff --git a/govc/session/login.go b/govc/session/login.go
index 2d0bbecad..87e720780 100644
--- a/govc/session/login.go
+++ b/govc/session/login.go
@@ -215,6 +215,13 @@ func (cmd *login) loginByToken(ctx context.Context, c *vim25.Client) error {
 		},
 	}
 
+	// something behind the LoginByToken scene requires a version from /sdk/vimServiceVersions.xml
+	// in the SOAPAction header. For example, if vim25.Version is "7.0" but the service version is "6.3",
+	// LoginByToken fails with: 'VersionMismatchFaultCode: Unsupported version URI "urn:vim25/7.0"'
+	if c.Version == vim25.Version {
+		_ = c.UseServiceVersion()
+	}
+
 	return session.NewManager(c).LoginByToken(c.WithHeader(ctx, header))
 }
 
diff --git a/sts/client.go b/sts/client.go
index bcd346b76..d98c56095 100644
--- a/sts/client.go
+++ b/sts/client.go
@@ -71,6 +71,9 @@ func (c *Client) RoundTrip(ctx context.Context, req, res soap.HasFault) error {
 
 // TokenRequest parameters for issuing a SAML token.
 // At least one of Userinfo or Certificate must be specified.
+// When `TokenRequest.Certificate` is set, the `tls.Certificate.PrivateKey` field must be set as it is required to sign the request.
+// When the `tls.Certificate.Certificate` field is not set, the request Assertion header is set to that of the TokenRequest.Token.
+// Otherwise `tls.Certificate.Certificate` is used as the BinarySecurityToken in the request.
 type TokenRequest struct {
 	Userinfo    *url.Userinfo    // Userinfo when set issues a Bearer token
 	Certificate *tls.Certificate // Certificate when set issues a HoK token
diff --git a/sts/client_test.go b/sts/client_test.go
index 030140396..8196e50ca 100644
--- a/sts/client_test.go
+++ b/sts/client_test.go
@@ -122,6 +122,7 @@ func TestIssueHOK(t *testing.T) {
 	if err != nil {
 		log.Fatal(err)
 	}
+	_ = c.UseServiceVersion()
 
 	if !c.IsVC() {
 		t.SkipNow()
@@ -161,6 +162,75 @@ func TestIssueHOK(t *testing.T) {
 	log.Printf("current time=%s", now)
 }
 
+func TestIssueTokenByToken(t *testing.T) {
+	ctx := context.Background()
+	url := os.Getenv("GOVC_TEST_URL")
+	if url == "" {
+		t.SkipNow()
+	}
+
+	u, err := soap.ParseURL(url)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	vc1, err := vim25.NewClient(ctx, soap.NewClient(u, true))
+	if err != nil {
+		log.Fatal(err)
+	}
+	_ = vc1.UseServiceVersion()
+
+	if !vc1.IsVC() {
+		t.SkipNow()
+	}
+
+	vc2, err := vim25.NewClient(ctx, soap.NewClient(u, true))
+	if err != nil {
+		log.Fatal(err)
+	}
+	_ = vc2.UseServiceVersion()
+
+	sts1, err := NewClient(ctx, vc1)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if err = solutionUserCreate(ctx, u.User, sts1, vc1); err != nil {
+		t.Fatal(err)
+	}
+
+	sts2, err := NewClient(ctx, vc2)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	req1 := TokenRequest{
+		Certificate: solutionUserCert(),
+		Delegatable: true,
+	}
+
+	signer1, err := sts1.Issue(ctx, req1)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	req2 := signer1.NewRequest()
+	// use Assertion header instead of BinarySecurityToken
+	req2.Certificate = &tls.Certificate{PrivateKey: req1.Certificate.PrivateKey}
+
+	signer2, err := sts2.Issue(ctx, req2)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	header := soap.Header{Security: signer2}
+
+	err = session.NewManager(vc2).LoginByToken(vc2.WithHeader(ctx, header))
+	if err != nil {
+		t.Fatal(err)
+	}
+}
+
 func TestIssueBearer(t *testing.T) {
 	ctx := context.Background()
 	url := os.Getenv("GOVC_TEST_URL")
@@ -177,6 +247,7 @@ func TestIssueBearer(t *testing.T) {
 	if err != nil {
 		log.Fatal(err)
 	}
+	_ = c.UseServiceVersion()
 
 	if !c.IsVC() {
 		t.SkipNow()
@@ -233,6 +304,7 @@ func TestIssueActAs(t *testing.T) {
 	if err != nil {
 		log.Fatal(err)
 	}
+	_ = c.UseServiceVersion()
 
 	if !c.IsVC() {
 		t.SkipNow()
diff --git a/sts/signer.go b/sts/signer.go
index 78cf20461..c6bf49d92 100644
--- a/sts/signer.go
+++ b/sts/signer.go
@@ -128,20 +128,28 @@ func (s *Signer) Sign(env soap.Envelope) ([]byte, error) {
 			req := x.RequestSecurityToken()
 			c14n = req.C14N()
 			body = req.String()
-			id := newID()
 
-			info.SecurityTokenReference = &internal.SecurityTokenReference{
-				Reference: &internal.SecurityReference{
-					URI:       "#" + id,
-					ValueType: "http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-x509-token-profile-1.0#X509v3",
-				},
-			}
-
-			header.BinarySecurityToken = &internal.BinarySecurityToken{
-				EncodingType: "http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-soap-message-security-1.0#Base64Binary",
-				ValueType:    "http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-x509-token-profile-1.0#X509v3",
-				ID:           id,
-				Value:        base64.StdEncoding.EncodeToString(s.Certificate.Certificate[0]),
+			if len(s.Certificate.Certificate) == 0 {
+				header.Assertion = s.Token
+				if err := s.setTokenReference(&info); err != nil {
+					return nil, err
+				}
+			} else {
+				id := newID()
+
+				header.BinarySecurityToken = &internal.BinarySecurityToken{
+					EncodingType: "http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-soap-message-security-1.0#Base64Binary",
+					ValueType:    "http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-x509-token-profile-1.0#X509v3",
+					ID:           id,
+					Value:        base64.StdEncoding.EncodeToString(s.Certificate.Certificate[0]),
+				}
+
+				info.SecurityTokenReference = &internal.SecurityTokenReference{
+					Reference: &internal.SecurityReference{
+						URI:       "#" + id,
+						ValueType: "http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-x509-token-profile-1.0#X509v3",
+					},
+				}
 			}
 		}
 		// When requesting HoK token for interactive user, request will have both priv. key and username/password.