diff --git a/staging/src/k8s.io/apiserver/pkg/authentication/request/bearertoken/bearertoken.go b/staging/src/k8s.io/apiserver/pkg/authentication/request/bearertoken/bearertoken.go
index 292b4f57d07..68c6ad918ae 100644
--- a/staging/src/k8s.io/apiserver/pkg/authentication/request/bearertoken/bearertoken.go
+++ b/staging/src/k8s.io/apiserver/pkg/authentication/request/bearertoken/bearertoken.go
@@ -22,6 +22,11 @@ import (
 	"strings"
 
 	"k8s.io/apiserver/pkg/authentication/authenticator"
+	"k8s.io/apiserver/pkg/warning"
+)
+
+const (
+	invalidTokenWithSpaceWarning = "the provided Authorization header contains extra space before the bearer token, and is ignored"
 )
 
 type Authenticator struct {
@@ -48,6 +53,10 @@ func (a *Authenticator) AuthenticateRequest(req *http.Request) (*authenticator.R
 
 	// Empty bearer tokens aren't valid
 	if len(token) == 0 {
+		// The space before the token case
+		if len(parts) == 3 {
+			warning.AddWarning(req.Context(), "", invalidTokenWithSpaceWarning)
+		}
 		return nil, false, nil
 	}
 
diff --git a/staging/src/k8s.io/apiserver/pkg/authentication/request/bearertoken/bearertoken_test.go b/staging/src/k8s.io/apiserver/pkg/authentication/request/bearertoken/bearertoken_test.go
index 5e982d5576f..d1e00babb87 100644
--- a/staging/src/k8s.io/apiserver/pkg/authentication/request/bearertoken/bearertoken_test.go
+++ b/staging/src/k8s.io/apiserver/pkg/authentication/request/bearertoken/bearertoken_test.go
@@ -25,6 +25,8 @@ import (
 
 	"k8s.io/apiserver/pkg/authentication/authenticator"
 	"k8s.io/apiserver/pkg/authentication/user"
+	genericapirequest "k8s.io/apiserver/pkg/endpoints/request"
+	"k8s.io/apiserver/pkg/warning"
 )
 
 func TestAuthenticateRequest(t *testing.T) {
@@ -128,6 +130,23 @@ func TestAuthenticateRequestBadValue(t *testing.T) {
 	}
 }
 
+type dummyRecorder struct {
+	agent string
+	text  string
+}
+
+func (r *dummyRecorder) AddWarning(agent, text string) {
+	r.agent = agent
+	r.text = text
+	return
+}
+
+func (r *dummyRecorder) getWarning() string {
+	return r.text
+}
+
+var _ warning.Recorder = &dummyRecorder{}
+
 func TestBearerToken(t *testing.T) {
 	tests := map[string]struct {
 		AuthorizationHeaders []string
@@ -137,6 +156,7 @@ func TestBearerToken(t *testing.T) {
 		ExpectedOK                   bool
 		ExpectedErr                  bool
 		ExpectedAuthorizationHeaders []string
+		ExpectedRecordedWarning      string
 	}{
 		"no header": {
 			AuthorizationHeaders:         nil,
@@ -184,6 +204,14 @@ func TestBearerToken(t *testing.T) {
 			ExpectedErr:                  true,
 			ExpectedAuthorizationHeaders: []string{"Bearer 123"},
 		},
+		"valid bearer token with a space": {
+			AuthorizationHeaders:         []string{"Bearer  token"},
+			ExpectedUserName:             "",
+			ExpectedOK:                   false,
+			ExpectedErr:                  false,
+			ExpectedAuthorizationHeaders: []string{"Bearer  token"},
+			ExpectedRecordedWarning:      invalidTokenWithSpaceWarning,
+		},
 		"error bearer token": {
 			AuthorizationHeaders: []string{"Bearer 123"},
 			TokenAuth: authenticator.TokenFunc(func(ctx context.Context, t string) (*authenticator.Response, bool, error) {
@@ -197,7 +225,10 @@ func TestBearerToken(t *testing.T) {
 	}
 
 	for k, tc := range tests {
-		req, _ := http.NewRequest("GET", "/", nil)
+		dc := dummyRecorder{agent: "", text: ""}
+		ctx := genericapirequest.NewDefaultContext()
+		ctxWithRecorder := warning.WithWarningRecorder(ctx, &dc)
+		req, _ := http.NewRequestWithContext(ctxWithRecorder, "GET", "/", nil)
 		for _, h := range tc.AuthorizationHeaders {
 			req.Header.Add("Authorization", h)
 		}
@@ -216,6 +247,10 @@ func TestBearerToken(t *testing.T) {
 			t.Errorf("%s: Expected username=%v, got %v", k, tc.ExpectedUserName, resp.User.GetName())
 			continue
 		}
+		if len(tc.ExpectedRecordedWarning) > 0 && tc.ExpectedRecordedWarning != dc.getWarning() {
+			t.Errorf("%s: Expected recorded warning=%v, got %v", k, tc.ExpectedRecordedWarning, dc.getWarning())
+			continue
+		}
 		if !reflect.DeepEqual(req.Header["Authorization"], tc.ExpectedAuthorizationHeaders) {
 			t.Errorf("%s: Expected headers=%#v, got %#v", k, tc.ExpectedAuthorizationHeaders, req.Header["Authorization"])
 			continue