diff --git a/auth/simple_token.go b/auth/simple_token.go
index 225791d8596f..ac55ad7f13fc 100644
--- a/auth/simple_token.go
+++ b/auth/simple_token.go
@@ -188,9 +188,9 @@ func (t *tokenSimple) info(ctx context.Context, token string, revision uint64) (
 
 func (t *tokenSimple) assign(ctx context.Context, username string, rev uint64) (string, error) {
 	// rev isn't used in simple token, it is only used in JWT
-	index := ctx.Value("index").(uint64)
-	simpleToken := ctx.Value("simpleToken").(string)
-	token := fmt.Sprintf("%s.%d", simpleToken, index)
+	index := ctx.Value(AuthenticateParamIndex{}).(uint64)
+	simpleTokenPrefix := ctx.Value(AuthenticateParamSimpleTokenPrefix{}).(string)
+	token := fmt.Sprintf("%s.%d", simpleTokenPrefix, index)
 	t.assignSimpleTokenToUser(username, token)
 
 	return token, nil
diff --git a/auth/simple_token_test.go b/auth/simple_token_test.go
index 862b88493fe1..1890521d4abe 100644
--- a/auth/simple_token_test.go
+++ b/auth/simple_token_test.go
@@ -29,7 +29,7 @@ func TestSimpleTokenDisabled(t *testing.T) {
 	explicitlyDisabled.disable()
 
 	for _, tp := range []*tokenSimple{initialState, explicitlyDisabled} {
-		ctx := context.WithValue(context.WithValue(context.TODO(), "index", uint64(1)), "simpleToken", "dummy")
+		ctx := context.WithValue(context.WithValue(context.TODO(), AuthenticateParamIndex{}, uint64(1)), AuthenticateParamSimpleTokenPrefix{}, "dummy")
 		token, err := tp.assign(ctx, "user1", 0)
 		if err != nil {
 			t.Fatal(err)
@@ -48,7 +48,7 @@ func TestSimpleTokenDisabled(t *testing.T) {
 func TestSimpleTokenAssign(t *testing.T) {
 	tp := newTokenProviderSimple(dummyIndexWaiter)
 	tp.enable()
-	ctx := context.WithValue(context.WithValue(context.TODO(), "index", uint64(1)), "simpleToken", "dummy")
+	ctx := context.WithValue(context.WithValue(context.TODO(), AuthenticateParamIndex{}, uint64(1)), AuthenticateParamSimpleTokenPrefix{}, "dummy")
 	token, err := tp.assign(ctx, "user1", 0)
 	if err != nil {
 		t.Fatal(err)
diff --git a/auth/store.go b/auth/store.go
index 363456cb26bc..a28d099147fe 100644
--- a/auth/store.go
+++ b/auth/store.go
@@ -81,6 +81,10 @@ type AuthInfo struct {
 	Revision uint64
 }
 
+// they are used for the keys of context in the parameters of Authenticate()
+type AuthenticateParamIndex struct{}
+type AuthenticateParamSimpleTokenPrefix struct{}
+
 type AuthStore interface {
 	// AuthEnable turns on the authentication feature
 	AuthEnable() error
@@ -1062,13 +1066,13 @@ func (as *authStore) WithRoot(ctx context.Context) context.Context {
 
 	var ctxForAssign context.Context
 	if ts := as.tokenProvider.(*tokenSimple); ts != nil {
-		ctx1 := context.WithValue(ctx, "index", uint64(0))
+		ctx1 := context.WithValue(ctx, AuthenticateParamIndex{}, uint64(0))
 		prefix, err := ts.genTokenPrefix()
 		if err != nil {
 			plog.Errorf("failed to generate prefix of internally used token")
 			return ctx
 		}
-		ctxForAssign = context.WithValue(ctx1, "simpleToken", prefix)
+		ctxForAssign = context.WithValue(ctx1, AuthenticateParamSimpleTokenPrefix{}, prefix)
 	} else {
 		ctxForAssign = ctx
 	}
diff --git a/auth/store_test.go b/auth/store_test.go
index 834274d273a2..b5e784d7f3fa 100644
--- a/auth/store_test.go
+++ b/auth/store_test.go
@@ -199,7 +199,7 @@ func TestUserChangePassword(t *testing.T) {
 	as, tearDown := setupAuthStore(t)
 	defer tearDown(t)
 
-	ctx1 := context.WithValue(context.WithValue(context.TODO(), "index", uint64(1)), "simpleToken", "dummy")
+	ctx1 := context.WithValue(context.WithValue(context.TODO(), AuthenticateParamIndex{}, uint64(1)), AuthenticateParamSimpleTokenPrefix{}, "dummy")
 	_, err := as.Authenticate(ctx1, "foo", "bar")
 	if err != nil {
 		t.Fatal(err)
@@ -210,7 +210,7 @@ func TestUserChangePassword(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	ctx2 := context.WithValue(context.WithValue(context.TODO(), "index", uint64(2)), "simpleToken", "dummy")
+	ctx2 := context.WithValue(context.WithValue(context.TODO(), AuthenticateParamIndex{}, uint64(2)), AuthenticateParamSimpleTokenPrefix{}, "dummy")
 	_, err = as.Authenticate(ctx2, "foo", "baz")
 	if err != nil {
 		t.Fatal(err)
@@ -461,7 +461,7 @@ func TestAuthInfoFromCtx(t *testing.T) {
 		t.Errorf("expected (nil, nil), got (%v, %v)", ai, err)
 	}
 
-	ctx = context.WithValue(context.WithValue(context.TODO(), "index", uint64(1)), "simpleToken", "dummy")
+	ctx = context.WithValue(context.WithValue(context.TODO(), AuthenticateParamIndex{}, uint64(1)), AuthenticateParamSimpleTokenPrefix{}, "dummy")
 	resp, err := as.Authenticate(ctx, "foo", "bar")
 	if err != nil {
 		t.Error(err)
@@ -494,7 +494,7 @@ func TestAuthDisable(t *testing.T) {
 	defer tearDown(t)
 
 	as.AuthDisable()
-	ctx := context.WithValue(context.WithValue(context.TODO(), "index", uint64(2)), "simpleToken", "dummy")
+	ctx := context.WithValue(context.WithValue(context.TODO(), AuthenticateParamIndex{}, uint64(2)), AuthenticateParamSimpleTokenPrefix{}, "dummy")
 	_, err := as.Authenticate(ctx, "foo", "bar")
 	if err != ErrAuthNotEnabled {
 		t.Errorf("expected %v, got %v", ErrAuthNotEnabled, err)
@@ -642,7 +642,7 @@ func TestHammerSimpleAuthenticate(t *testing.T) {
 			go func(user string) {
 				defer wg.Done()
 				token := fmt.Sprintf("%s(%d)", user, i)
-				ctx := context.WithValue(context.WithValue(context.TODO(), "index", uint64(1)), "simpleToken", token)
+				ctx := context.WithValue(context.WithValue(context.TODO(), AuthenticateParamIndex{}, uint64(1)), AuthenticateParamSimpleTokenPrefix{}, token)
 				if _, err := as.Authenticate(ctx, user, "123"); err != nil {
 					t.Fatal(err)
 				}
diff --git a/etcdserver/apply.go b/etcdserver/apply.go
index dfd09a464c9d..ce4bfbfbcc9d 100644
--- a/etcdserver/apply.go
+++ b/etcdserver/apply.go
@@ -20,6 +20,7 @@ import (
 	"sort"
 	"time"
 
+	"github.com/coreos/etcd/auth"
 	pb "github.com/coreos/etcd/etcdserver/etcdserverpb"
 	"github.com/coreos/etcd/lease"
 	"github.com/coreos/etcd/mvcc"
@@ -652,7 +653,7 @@ func (a *applierV3backend) AuthDisable() (*pb.AuthDisableResponse, error) {
 }
 
 func (a *applierV3backend) Authenticate(r *pb.InternalAuthenticateRequest) (*pb.AuthenticateResponse, error) {
-	ctx := context.WithValue(context.WithValue(a.s.ctx, "index", a.s.consistIndex.ConsistentIndex()), "simpleToken", r.SimpleToken)
+	ctx := context.WithValue(context.WithValue(a.s.ctx, auth.AuthenticateParamIndex{}, a.s.consistIndex.ConsistentIndex()), auth.AuthenticateParamSimpleTokenPrefix{}, r.SimpleToken)
 	resp, err := a.s.AuthStore().Authenticate(ctx, r.Name, r.Password)
 	if resp != nil {
 		resp.Header = newHeader(a.s)