diff --git a/e2e_test/context_test.go b/e2e_test/context_test.go
index 914aad9..6a93070 100644
--- a/e2e_test/context_test.go
+++ b/e2e_test/context_test.go
@@ -36,7 +36,6 @@ func TestContextCancelOnWaitingForBrowser(t *testing.T) {
 				TokenURL: testServer.URL + "/token",
 			},
 		},
-		Logf: t.Logf,
 	}
 	_, err := oauth2cli.GetToken(ctx, cfg)
 	if err == nil {
@@ -73,9 +72,7 @@ func TestContextCancelOnLocalServerReadyChan(t *testing.T) {
 				TokenURL: testServer.URL + "/token",
 			},
 		},
-		LocalServerReadyChan: openBrowserCh,
-		Logf:                 t.Logf,
-	}
+		LocalServerReadyChan: openBrowserCh}
 	_, err := oauth2cli.GetToken(ctx, cfg)
 	if err == nil {
 		t.Errorf("GetToken wants error but was nil")
diff --git a/e2e_test/e2e_test.go b/e2e_test/e2e_test.go
index 2dd9490..4d29550 100644
--- a/e2e_test/e2e_test.go
+++ b/e2e_test/e2e_test.go
@@ -62,7 +62,6 @@ func TestHappyPath(t *testing.T) {
 			},
 			LocalServerReadyChan:  openBrowserCh,
 			LocalServerMiddleware: loggingMiddleware(t),
-			Logf:                  t.Logf,
 		}
 		token, err := oauth2cli.GetToken(ctx, cfg)
 		if err != nil {
@@ -132,9 +131,7 @@ func TestRedirectURLHostname(t *testing.T) {
 			},
 			RedirectURLHostname:   "127.0.0.1",
 			LocalServerReadyChan:  openBrowserCh,
-			LocalServerMiddleware: loggingMiddleware(t),
-			Logf:                  t.Logf,
-		}
+			LocalServerMiddleware: loggingMiddleware(t)}
 		token, err := oauth2cli.GetToken(ctx, cfg)
 		if err != nil {
 			t.Errorf("could not get a token: %s", err)
@@ -214,9 +211,7 @@ func TestSuccessRedirect(t *testing.T) {
 			LocalServerReadyChan:  openBrowserCh,
 			LocalServerMiddleware: loggingMiddleware(t),
 			SuccessRedirectURL:    sr.URL + "/success",
-			FailureRedirectURL:    sr.URL + "/failure",
-			Logf:                  t.Logf,
-		}
+			FailureRedirectURL:    sr.URL + "/failure"}
 		token, err := oauth2cli.GetToken(ctx, cfg)
 		if err != nil {
 			t.Errorf("could not get a token: %s", err)
diff --git a/e2e_test/error_test.go b/e2e_test/error_test.go
index f5e288f..d0e07a2 100644
--- a/e2e_test/error_test.go
+++ b/e2e_test/error_test.go
@@ -46,7 +46,6 @@ func TestErrorAuthorizationResponse(t *testing.T) {
 				},
 			},
 			LocalServerReadyChan: openBrowserCh,
-			Logf:                 t.Logf,
 		}
 		_, err := oauth2cli.GetToken(ctx, cfg)
 		if err == nil {
@@ -113,9 +112,7 @@ func TestFailureRedirect(t *testing.T) {
 			},
 			LocalServerReadyChan: openBrowserCh,
 			SuccessRedirectURL:   pageServer.URL + "/success",
-			FailureRedirectURL:   pageServer.URL + "/failure",
-			Logf:                 t.Logf,
-		}
+			FailureRedirectURL:   pageServer.URL + "/failure"}
 		_, err := oauth2cli.GetToken(ctx, cfg)
 		if err == nil {
 			t.Errorf("GetToken wants error but was nil")
@@ -166,9 +163,7 @@ func TestErrorTokenResponse(t *testing.T) {
 					TokenURL: testServer.URL + "/token",
 				},
 			},
-			LocalServerReadyChan: openBrowserCh,
-			Logf:                 t.Logf,
-		}
+			LocalServerReadyChan: openBrowserCh}
 		_, err := oauth2cli.GetToken(ctx, cfg)
 		if err == nil {
 			t.Errorf("GetToken wants error but nil")
diff --git a/e2e_test/localserveropts_test.go b/e2e_test/localserveropts_test.go
index 5afe7a6..fdf029b 100644
--- a/e2e_test/localserveropts_test.go
+++ b/e2e_test/localserveropts_test.go
@@ -58,7 +58,6 @@ func TestLocalServerCallbackPath(t *testing.T) {
 			LocalServerCallbackPath: "/callback",
 			LocalServerReadyChan:    openBrowserCh,
 			LocalServerMiddleware:   loggingMiddleware(t),
-			Logf:                    t.Logf,
 		}
 		token, err := oauth2cli.GetToken(ctx, cfg)
 		if err != nil {
diff --git a/e2e_test/pkce_test.go b/e2e_test/pkce_test.go
index bf2e70e..978b1cd 100644
--- a/e2e_test/pkce_test.go
+++ b/e2e_test/pkce_test.go
@@ -76,7 +76,6 @@ func TestPKCE(t *testing.T) {
 			},
 			LocalServerReadyChan:  openBrowserCh,
 			LocalServerMiddleware: loggingMiddleware(t),
-			Logf:                  t.Logf,
 		}
 		token, err := oauth2cli.GetToken(ctx, cfg)
 		if err != nil {
diff --git a/e2e_test/tls_test.go b/e2e_test/tls_test.go
index 376d98e..1a47fc1 100644
--- a/e2e_test/tls_test.go
+++ b/e2e_test/tls_test.go
@@ -59,7 +59,6 @@ func TestTLS(t *testing.T) {
 			LocalServerKeyFile:    "testdata/server.key",
 			LocalServerReadyChan:  openBrowserCh,
 			LocalServerMiddleware: loggingMiddleware(t),
-			Logf:                  t.Logf,
 		}
 		token, err := oauth2cli.GetToken(ctx, cfg)
 		if err != nil {
diff --git a/example/main.go b/example/main.go
index e49d792..c92c26b 100644
--- a/example/main.go
+++ b/example/main.go
@@ -5,6 +5,7 @@ import (
 	"flag"
 	"fmt"
 	"log"
+	"log/slog"
 	"os"
 	"strings"
 
@@ -17,6 +18,7 @@ import (
 
 func init() {
 	log.SetFlags(log.Lshortfile | log.Lmicroseconds)
+	slog.SetLogLoggerLevel(slog.LevelDebug)
 }
 
 type cmdOptions struct {
@@ -40,7 +42,7 @@ func main() {
 	flag.StringVar(&o.localServerKey, "local-server-key", "", "Path to a key file for the local server (optional)")
 	flag.Parse()
 	if o.clientID == "" {
-		log.Printf(`You need to set oauth2 credentials.
+		slog.Error(`You need to set oauth2 credentials.
 Open https://console.cloud.google.com/apis/credentials and create a client.
 Then set the following options:`)
 		flag.PrintDefaults()
@@ -48,7 +50,7 @@ Then set the following options:`)
 		return
 	}
 	if o.localServerCert != "" {
-		log.Printf("Using the TLS certificate: %s", o.localServerCert)
+		slog.Debug(`Using the TLS certificate`, "path", o.localServerCert)
 	}
 
 	pkce, err := oauth2params.NewPKCE()
@@ -72,7 +74,6 @@ Then set the following options:`)
 		LocalServerReadyChan: ready,
 		LocalServerCertFile:  o.localServerCert,
 		LocalServerKeyFile:   o.localServerKey,
-		Logf:                 log.Printf,
 	}
 
 	ctx := context.Background()
@@ -80,9 +81,9 @@ Then set the following options:`)
 	eg.Go(func() error {
 		select {
 		case url := <-ready:
-			log.Printf("Open %s", url)
+			slog.Info("Open", "url", url)
 			if err := browser.OpenURL(url); err != nil {
-				log.Printf("could not open the browser: %s", err)
+				slog.Error("could not open the browser", "error", err)
 			}
 			return nil
 		case <-ctx.Done():
diff --git a/go.work.sum b/go.work.sum
index 1a6b87e..eaf13f1 100644
--- a/go.work.sum
+++ b/go.work.sum
@@ -3,7 +3,9 @@ cloud.google.com/go v0.116.0 h1:B3fRrSDkLRt5qSHWe40ERJvhvnQwdZiHu0bJOpldweE=
 cloud.google.com/go v0.116.0/go.mod h1:cEPSRWPzZEswwdr9BxE6ChEn01dWlTaF05LiC2Xs70U=
 cloud.google.com/go/ai v0.8.0/go.mod h1:t3Dfk4cM61sytiggo2UyGsDVW3RF1qGZaUKDrZFyqkE=
 cloud.google.com/go/auth v0.13.0/go.mod h1:COOjD9gwfKNKz+IIduatIhYJQIc0mG3H102r/EMxX6Q=
+cloud.google.com/go/auth v0.15.0/go.mod h1:WJDGqZ1o9E9wKIL+IwStfyn/+s59zl4Bi+1KQNVXLZ8=
 cloud.google.com/go/auth/oauth2adapt v0.2.6/go.mod h1:AlmsELtlEBnaNTL7jCj8VQFLy6mbZv0s4Q7NGBeQ5E8=
+cloud.google.com/go/auth/oauth2adapt v0.2.7/go.mod h1:NTbTTzfvPl1Y3V1nPpOgl2w6d/FjO7NNUQaWSox6ZMc=
 cloud.google.com/go/compute v1.6.1 h1:2sMmt8prCn7DPaG4Pmh0N3Inmc8cT8ae5k1M6VJ9Wqc=
 cloud.google.com/go/compute v1.6.1/go.mod h1:g85FgpzFvNULZ+S8AYq87axRKuf2Kh7deLqV/jJ3thU=
 cloud.google.com/go/compute/metadata v0.6.0 h1:A6hENjEsCDtC1k8byVsgwvVcioamEHvZ4j01OwKxG9I=
@@ -35,6 +37,7 @@ github.com/golang/groupcache v0.0.0-20210331224755-41bb18bfe9da/go.mod h1:cIg4er
 github.com/golangci/modinfo v0.3.3/go.mod h1:wytF1M5xl9u0ij8YSvhkEVPP3M5Mc7XLl1pxH3B2aUM=
 github.com/google/generative-ai-go v0.19.0/go.mod h1:JYolL13VG7j79kM5BtHz4qwONHkeJQzOCkKXnpqtS/E=
 github.com/google/s2a-go v0.1.8/go.mod h1:6iNWHTpQ+nfNRN5E00MSdfDwVesa8hhS32PhPO8deJA=
+github.com/google/s2a-go v0.1.9/go.mod h1:YA0Ei2ZQL3acow2O62kdp9UlnvMmU7kA6Eutn0dXayM=
 github.com/google/uuid v1.6.0/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
 github.com/googleapis/enterprise-certificate-proxy v0.3.4/go.mod h1:YKe7cfqYXjKGpGvmSg28/fFvhNzinZQm8DGnaburhGA=
 github.com/googleapis/gax-go/v2 v2.14.1/go.mod h1:Hb/NubMaVM88SrNkvl8X/o8XWwDJEPqouaLeN2IUxoA=
@@ -64,6 +67,7 @@ github.com/power-devops/perfstat v0.0.0-20210106213030-5aafc221ea8c/go.mod h1:Om
 github.com/quasilyte/go-ruleguard/rules v0.0.0-20211022131956-028d6511ab71/go.mod h1:4cgAphtvu7Ftv7vOT2ZOYhC6CvBxZixcasr8qIOTA50=
 github.com/sagikazarmark/crypt v0.6.0/go.mod h1:U8+INwJo3nBv1m6A/8OBXAq7Jnpspk5AxSgDyEQcea8=
 github.com/shirou/gopsutil/v4 v4.25.1/go.mod h1:RoUCUpndaJFtT+2zsZzzmhvbfGoDCJ7nFXKJf8GqJbI=
+github.com/shirou/gopsutil/v4 v4.25.2/go.mod h1:34gBYJzyqCDT11b6bMHP0XCvWeU3J61XRT7a2EmCRTA=
 github.com/tklauser/go-sysconf v0.3.12/go.mod h1:Ho14jnntGE1fpdOqQEEaiKRpvIavV0hSfmBq8nJbHYI=
 github.com/tklauser/numcpus v0.6.1/go.mod h1:1XfjsgE2zo8GVw7POkMbHENHzVg3GzmoZ9fESEdAacY=
 github.com/valyala/bytebufferpool v1.0.0/go.mod h1:6bBcMArwyJ5K/AmCkWv1jt77kVWyCJ6HpOuEn7z0Csc=
@@ -75,22 +79,33 @@ go.etcd.io/etcd/client/pkg/v3 v3.5.4/go.mod h1:IJHfcCEKxYu1Os13ZdwCwIUTUVGYTSAM3
 go.etcd.io/etcd/client/v2 v2.305.4/go.mod h1:Ud+VUwIi9/uQHOMA+4ekToJ12lTxlv0zB/+DHwTGEbU=
 go.etcd.io/etcd/client/v3 v3.5.4/go.mod h1:ZaRkVgBZC+L+dLCjTcF1hRXpgZXQPOvnA/Ak/gq3kiY=
 go.opencensus.io v0.24.0/go.mod h1:vNK8G9p7aAivkbmorf4v+7Hgx+Zs0yY+0fOtgBfjQKo=
+go.opentelemetry.io/auto/sdk v1.1.0/go.mod h1:3wSPjt5PWp2RhlCcmmOial7AvC4DQqZb7a7wCow3W8A=
 go.opentelemetry.io/contrib/detectors/gcp v1.29.0/go.mod h1:GW2aWZNwR2ZxDLdv8OyC2G8zkRoQBuURgV7RPQgcPoU=
 go.opentelemetry.io/contrib/instrumentation/google.golang.org/grpc/otelgrpc v0.54.0/go.mod h1:B9yO6b04uB80CzjedvewuqDhxJxi11s7/GtiGa8bAjI=
+go.opentelemetry.io/contrib/instrumentation/google.golang.org/grpc/otelgrpc v0.59.0/go.mod h1:ijPqXp5P6IRRByFVVg9DY8P5HkxkHE5ARIa+86aXPf4=
 go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.54.0/go.mod h1:L7UH0GbB0p47T4Rri3uHjbpCFYrVrwc1I25QhNPiGK8=
+go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.59.0/go.mod h1:FRmFuRJfag1IZ2dPkHnEoSFVgTVPUd2qf5Vi69hLb8I=
 go.opentelemetry.io/otel v1.29.0/go.mod h1:N/WtXPs1CNCUEx+Agz5uouwCba+i+bJGFicT8SR4NP8=
+go.opentelemetry.io/otel v1.34.0/go.mod h1:OWFPOQ+h4G8xpyjgqo4SxJYdDQ/qmRH+wivy7zzx9oI=
 go.opentelemetry.io/otel/metric v1.29.0/go.mod h1:auu/QWieFVWx+DmQOUMgj0F8LHWdgalxXqvp7BII/W8=
+go.opentelemetry.io/otel/metric v1.34.0/go.mod h1:CEDrp0fy2D0MvkXE+dPV7cMi8tWZwX3dmaIhwPOaqHE=
 go.opentelemetry.io/otel/sdk v1.29.0/go.mod h1:pM8Dx5WKnvxLCb+8lG1PRNIDxu9g9b9g59Qr7hfAAok=
 go.opentelemetry.io/otel/sdk/metric v1.29.0/go.mod h1:6zZLdCl2fkauYoZIOn/soQIDSWFmNSRcICarHfuhNJQ=
 go.opentelemetry.io/otel/trace v1.29.0/go.mod h1:eHl3w0sp3paPkYstJOmAimxhiFXPg+MMTlEh3nsQgWQ=
+go.opentelemetry.io/otel/trace v1.34.0/go.mod h1:Svm7lSjQD7kG7KJ/MUHPVXSDGz2OX4h0M2jHBhmSfRE=
 golang.org/x/crypto v0.32.0/go.mod h1:ZnnJkOaASj8g0AjIduWNlq2NRxL0PlBrbKVyZ6V/Ugc=
+golang.org/x/crypto v0.35.0/go.mod h1:dy7dXNW32cAb/6/PRuTNsix8T+vJAqvuIy5Bli/x0YQ=
 golang.org/x/sys v0.28.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
 golang.org/x/telemetry v0.0.0-20240521205824-bda55230c457/go.mod h1:pRgIJT+bRLFKnoM1ldnzKoxTIn14Yxz928LQRYYgIN0=
 golang.org/x/time v0.8.0/go.mod h1:3BpzKBy/shNhVucY/MWOyx10tF3SFh9QdLuxbVysPQM=
+golang.org/x/time v0.10.0/go.mod h1:3BpzKBy/shNhVucY/MWOyx10tF3SFh9QdLuxbVysPQM=
 golang.org/x/xerrors v0.0.0-20220517211312-f3a8303e98df/go.mod h1:K8+ghG5WaK9qNqU5K3HdILfMLy1f3aNYFI/wnl100a8=
 google.golang.org/api v0.215.0/go.mod h1:fta3CVtuJYOEdugLNWm6WodzOS8KdFckABwN4I40hzY=
+google.golang.org/api v0.223.0/go.mod h1:C+RS7Z+dDwds2b+zoAk5hN/eSfsiCn0UDrYof/M4d2M=
 google.golang.org/appengine v1.6.7/go.mod h1:8WjMMxjGQR8xUklV/ARdw2HLXBOI7O7uCIDZVag1xfc=
 google.golang.org/genproto v0.0.0-20241118233622-e639e219e697/go.mod h1:JJrvXBWRZaFMxBufik1a4RpFw4HhgVtBBWQeQgUj2cc=
 google.golang.org/genproto/googleapis/api v0.0.0-20241209162323-e6fa225c2576/go.mod h1:1R3kvZ1dtP3+4p4d3G8uJ8rFk/fWlScl38vanWACI08=
 google.golang.org/genproto/googleapis/rpc v0.0.0-20241223144023-3abc09e42ca8/go.mod h1:lcTa1sDdWEIHMWlITnIczmw5w60CF9ffkb8Z+DVmmjA=
+google.golang.org/genproto/googleapis/rpc v0.0.0-20250219182151-9fdb1cabc7b2/go.mod h1:LuRYeWDFV6WOn90g357N17oMCaxpgCnbi/44qJvDn2I=
 google.golang.org/grpc v1.67.3/go.mod h1:YGaHCc6Oap+FzBJTZLBzkGSYt/cvGPFTPxkn7QfSU8s=
+google.golang.org/grpc v1.70.0/go.mod h1:ofIJqVKDXx/JiXrwr2IG4/zwdH9txy3IlF40RmcJSQw=
diff --git a/oauth2cli.go b/oauth2cli.go
index 03370c2..c9a3530 100644
--- a/oauth2cli.go
+++ b/oauth2cli.go
@@ -5,6 +5,7 @@ package oauth2cli
 import (
 	"context"
 	"fmt"
+	"log/slog"
 	"net/http"
 
 	"github.com/int128/oauth2cli/oauth2params"
@@ -99,9 +100,6 @@ type Config struct {
 	SuccessRedirectURL string
 	// Redirect URL upon failed login
 	FailureRedirectURL string
-
-	// Logger function for debug.
-	Logf func(format string, args ...interface{})
 }
 
 func (cfg *Config) isLocalServerHTTPS() bool {
@@ -133,9 +131,6 @@ func (cfg *Config) validateAndSetDefaults() error {
 		(cfg.SuccessRedirectURL == "" && cfg.FailureRedirectURL != "") {
 		return fmt.Errorf("when using success and failure redirect URLs, set both URLs")
 	}
-	if cfg.Logf == nil {
-		cfg.Logf = func(string, ...interface{}) {}
-	}
 	return nil
 }
 
@@ -158,7 +153,7 @@ func GetToken(ctx context.Context, cfg Config) (*oauth2.Token, error) {
 	if err != nil {
 		return nil, fmt.Errorf("authorization error: %w", err)
 	}
-	cfg.Logf("oauth2cli: exchanging the code and token")
+	slog.DebugContext(ctx, "oauth2cli: exchanging the code and token")
 	token, err := cfg.OAuth2Config.Exchange(ctx, code, cfg.TokenRequestOptions...)
 	if err != nil {
 		return nil, fmt.Errorf("could not exchange the code and token: %w", err)
diff --git a/server.go b/server.go
index 0ffc8f7..10e8e12 100644
--- a/server.go
+++ b/server.go
@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"log/slog"
 	"net"
 	"net/http"
 	"net/url"
@@ -39,14 +40,17 @@ func receiveCodeViaLocalServer(ctx context.Context, cfg *Config) (string, error)
 			config: cfg,
 			respCh: respCh,
 		}),
+		BaseContext: func(net.Listener) context.Context {
+			return ctx
+		},
 	}
 	shutdownCh := make(chan struct{})
 	var resp *authorizationResponse
 	var eg errgroup.Group
 	eg.Go(func() error {
 		defer close(respCh)
-		cfg.Logf("oauth2cli: starting a server at %s", localServerListener.Addr())
-		defer cfg.Logf("oauth2cli: stopped the server")
+		slog.DebugContext(ctx, "oauth2cli: starting a server", "address", localServerListener.Addr())
+		defer slog.DebugContext(ctx, "oauth2cli: stopped the server")
 		if cfg.isLocalServerHTTPS() {
 			if err := server.ServeTLS(localServerListener, cfg.LocalServerCertFile, cfg.LocalServerKeyFile); err != nil {
 				if errors.Is(err, http.ErrServerClosed) {
@@ -78,11 +82,11 @@ func receiveCodeViaLocalServer(ctx context.Context, cfg *Config) (string, error)
 		// Gracefully shutdown the server in the timeout.
 		// If the server has not started, Shutdown returns nil and this returns immediately.
 		// If Shutdown has failed, force-close the server.
-		cfg.Logf("oauth2cli: shutting down the server")
+		slog.DebugContext(ctx, "oauth2cli: shutting down the server")
 		ctx, cancel := context.WithTimeout(ctx, 500*time.Millisecond)
 		defer cancel()
 		if err := server.Shutdown(ctx); err != nil {
-			cfg.Logf("oauth2cli: force-closing the server: shutdown failed: %s", err)
+			slog.DebugContext(ctx, "oauth2cli: force-closing the server", "error", err)
 			_ = server.Close()
 			return nil
 		}
@@ -153,7 +157,7 @@ func (h *localServerHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 
 func (h *localServerHandler) handleIndex(w http.ResponseWriter, r *http.Request) {
 	authCodeURL := h.config.OAuth2Config.AuthCodeURL(h.config.State, h.config.AuthCodeOptions...)
-	h.config.Logf("oauth2cli: sending redirect to %s", authCodeURL)
+	slog.DebugContext(r.Context(), "oauth2cli: sending redirect", "url", authCodeURL)
 	http.Redirect(w, r, authCodeURL, http.StatusFound)
 }