diff --git a/auth/auth_test.go b/auth/auth_test.go
index 69127b22..53daf79f 100644
--- a/auth/auth_test.go
+++ b/auth/auth_test.go
@@ -19,7 +19,6 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
-	"io/ioutil"
 	"log"
 	"net/http"
 	"os"
@@ -74,10 +73,10 @@ func TestMain(m *testing.M) {
 	testCookieVerifier, err = cookieVerifierForTests(context.Background())
 	logFatal(err)
 
-	testGetUserResponse, err = ioutil.ReadFile("../testdata/get_user.json")
+	testGetUserResponse, err = os.ReadFile("../testdata/get_user.json")
 	logFatal(err)
 
-	testGetDisabledUserResponse, err = ioutil.ReadFile("../testdata/get_disabled_user.json")
+	testGetDisabledUserResponse, err = os.ReadFile("../testdata/get_disabled_user.json")
 	logFatal(err)
 
 	testIDToken = getIDToken(nil)
@@ -1290,7 +1289,7 @@ type mockKeySource struct {
 }
 
 func newMockKeySource(filePath string) (*mockKeySource, error) {
-	certs, err := ioutil.ReadFile(filePath)
+	certs, err := os.ReadFile(filePath)
 	if err != nil {
 		return nil, err
 	}
diff --git a/auth/tenant_mgt_test.go b/auth/tenant_mgt_test.go
index aaf65b52..574c91f1 100644
--- a/auth/tenant_mgt_test.go
+++ b/auth/tenant_mgt_test.go
@@ -18,8 +18,8 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
-	"io/ioutil"
 	"net/http"
+	"os"
 	"reflect"
 	"sort"
 	"strconv"
@@ -178,7 +178,7 @@ func TestTenantGetUserByPhoneNumber(t *testing.T) {
 }
 
 func TestTenantListUsers(t *testing.T) {
-	testListUsersResponse, err := ioutil.ReadFile("../testdata/list_users.json")
+	testListUsersResponse, err := os.ReadFile("../testdata/list_users.json")
 	if err != nil {
 		t.Fatal(err)
 	}
diff --git a/auth/token_generator_test.go b/auth/token_generator_test.go
index 6ed5144e..0aaf7f3c 100644
--- a/auth/token_generator_test.go
+++ b/auth/token_generator_test.go
@@ -20,9 +20,10 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
-	"io/ioutil"
+	"io"
 	"net/http"
 	"net/http/httptest"
+	"os"
 	"strings"
 	"testing"
 
@@ -90,7 +91,7 @@ func TestEncodeInvalidPayload(t *testing.T) {
 }
 
 func TestServiceAccountSigner(t *testing.T) {
-	b, err := ioutil.ReadFile("../testdata/service_account.json")
+	b, err := os.ReadFile("../testdata/service_account.json")
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -331,7 +332,7 @@ func iamServer(t *testing.T, serviceAcct, signature string) *httptest.Server {
 	wantPath := fmt.Sprintf("/v1/projects/-/serviceAccounts/%s:signBlob", serviceAcct)
 	handler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		defer r.Body.Close()
-		reqBody, err := ioutil.ReadAll(r.Body)
+		reqBody, err := io.ReadAll(r.Body)
 		if err != nil {
 			t.Fatal(err)
 		}
diff --git a/auth/token_verifier.go b/auth/token_verifier.go
index fe6cdf0c..8ab81da3 100644
--- a/auth/token_verifier.go
+++ b/auth/token_verifier.go
@@ -26,7 +26,7 @@ import (
 	"encoding/pem"
 	"errors"
 	"fmt"
-	"io/ioutil"
+	"io"
 	"net/http"
 	"strconv"
 	"strings"
@@ -417,7 +417,7 @@ func (k *httpKeySource) refreshKeys(ctx context.Context) error {
 	}
 	defer resp.Body.Close()
 
-	contents, err := ioutil.ReadAll(resp.Body)
+	contents, err := io.ReadAll(resp.Body)
 	if err != nil {
 		return err
 	}
diff --git a/auth/token_verifier_test.go b/auth/token_verifier_test.go
index e24d7d1c..3a560651 100644
--- a/auth/token_verifier_test.go
+++ b/auth/token_verifier_test.go
@@ -19,8 +19,8 @@ import (
 	"errors"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"net/http"
+	"os"
 	"testing"
 	"time"
 
@@ -51,7 +51,7 @@ func TestNewIDTokenVerifier(t *testing.T) {
 }
 
 func TestHTTPKeySource(t *testing.T) {
-	data, err := ioutil.ReadFile("../testdata/public_certs.json")
+	data, err := os.ReadFile("../testdata/public_certs.json")
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -68,7 +68,7 @@ func TestHTTPKeySource(t *testing.T) {
 }
 
 func TestHTTPKeySourceWithClient(t *testing.T) {
-	data, err := ioutil.ReadFile("../testdata/public_certs.json")
+	data, err := os.ReadFile("../testdata/public_certs.json")
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -160,7 +160,7 @@ func TestFindMaxAge(t *testing.T) {
 }
 
 func TestParsePublicKeys(t *testing.T) {
-	b, err := ioutil.ReadFile("../testdata/public_certs.json")
+	b, err := os.ReadFile("../testdata/public_certs.json")
 	if err != nil {
 		t.Fatal(err)
 	}
diff --git a/auth/user_mgt_test.go b/auth/user_mgt_test.go
index 094716c2..6464fc53 100644
--- a/auth/user_mgt_test.go
+++ b/auth/user_mgt_test.go
@@ -20,9 +20,10 @@ import (
 	"encoding/base64"
 	"encoding/json"
 	"fmt"
-	"io/ioutil"
+	"io"
 	"net/http"
 	"net/http/httptest"
+	"os"
 	"reflect"
 	"sort"
 	"strconv"
@@ -545,7 +546,7 @@ func TestGetNonExistingUser(t *testing.T) {
 }
 
 func TestListUsers(t *testing.T) {
-	testListUsersResponse, err := ioutil.ReadFile("../testdata/list_users.json")
+	testListUsersResponse, err := os.ReadFile("../testdata/list_users.json")
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -2542,7 +2543,7 @@ func echoServer(resp interface{}, t *testing.T) *mockAuthServer {
 
 	handler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		defer r.Body.Close()
-		reqBody, err := ioutil.ReadAll(r.Body)
+		reqBody, err := io.ReadAll(r.Body)
 		if err != nil {
 			t.Fatal(err)
 		}
diff --git a/db/db_test.go b/db/db_test.go
index 68517189..35192d0e 100644
--- a/db/db_test.go
+++ b/db/db_test.go
@@ -18,7 +18,7 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
-	"io/ioutil"
+	"io"
 	"log"
 	"net/http"
 	"net/http/httptest"
@@ -395,7 +395,7 @@ type testReq struct {
 
 func newTestReq(r *http.Request) (*testReq, error) {
 	defer r.Body.Close()
-	b, err := ioutil.ReadAll(r.Body)
+	b, err := io.ReadAll(r.Body)
 	if err != nil {
 		return nil, err
 	}
diff --git a/firebase.go b/firebase.go
index 39d1c4e2..d974d4b2 100644
--- a/firebase.go
+++ b/firebase.go
@@ -21,7 +21,6 @@ import (
 	"context"
 	"encoding/json"
 	"errors"
-	"io/ioutil"
 	"os"
 	"sync"
 
@@ -231,7 +230,7 @@ func getConfigDefaults() (*Config, error) {
 		dat = []byte(confFileName)
 	} else {
 		var err error
-		if dat, err = ioutil.ReadFile(confFileName); err != nil {
+		if dat, err = os.ReadFile(confFileName); err != nil {
 			return nil, err
 		}
 	}
diff --git a/firebase_test.go b/firebase_test.go
index 789ea188..25ec1b88 100644
--- a/firebase_test.go
+++ b/firebase_test.go
@@ -18,7 +18,6 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
-	"io/ioutil"
 	"log"
 	"net/http"
 	"net/http/httptest"
@@ -688,7 +687,7 @@ func compareConfig(got *App, want *Config, t *testing.T) {
 // mockServiceAcct generates a service account configuration with the provided URL as the
 // token_url value.
 func mockServiceAcct(tokenURL string) ([]byte, error) {
-	b, err := ioutil.ReadFile("testdata/service_account.json")
+	b, err := os.ReadFile("testdata/service_account.json")
 	if err != nil {
 		return nil, err
 	}
diff --git a/integration/auth/auth_test.go b/integration/auth/auth_test.go
index 3bf43461..641cdbab 100644
--- a/integration/auth/auth_test.go
+++ b/integration/auth/auth_test.go
@@ -24,7 +24,7 @@ import (
 	"encoding/json"
 	"flag"
 	"fmt"
-	"io/ioutil"
+	"io"
 	"log"
 	"math/rand"
 	"net/http"
@@ -86,7 +86,7 @@ func TestCustomToken(t *testing.T) {
 func TestCustomTokenWithoutServiceAccount(t *testing.T) {
 	// Create a TokenSource from the service account. This makes the private key not accessible
 	// to the Firebase APIs.
-	b, err := ioutil.ReadFile(internal.Resource("integration_cert.json"))
+	b, err := os.ReadFile(internal.Resource("integration_cert.json"))
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -382,7 +382,7 @@ func postRequest(url string, req []byte) ([]byte, error) {
 	if resp.StatusCode != http.StatusOK {
 		return nil, fmt.Errorf("unexpected http status code: %d", resp.StatusCode)
 	}
-	return ioutil.ReadAll(resp.Body)
+	return io.ReadAll(resp.Body)
 }
 
 // deleteUser makes a best effort attempt to delete the given user.
diff --git a/integration/db/db_test.go b/integration/db/db_test.go
index 9a5d715a..32c64b45 100644
--- a/integration/db/db_test.go
+++ b/integration/db/db_test.go
@@ -21,7 +21,7 @@ import (
 	"encoding/json"
 	"flag"
 	"fmt"
-	"io/ioutil"
+	"io"
 	"log"
 	"net/http"
 	"os"
@@ -137,7 +137,7 @@ func initGuestClient(pid string) (*db.Client, error) {
 }
 
 func initRules() {
-	b, err := ioutil.ReadFile(internal.Resource("dinosaurs_index.json"))
+	b, err := os.ReadFile(internal.Resource("dinosaurs_index.json"))
 	if err != nil {
 		log.Fatalln(err)
 	}
@@ -162,7 +162,7 @@ func initRules() {
 	}
 	defer resp.Body.Close()
 
-	b, err = ioutil.ReadAll(resp.Body)
+	b, err = io.ReadAll(resp.Body)
 	if err != nil {
 		log.Fatalln(err)
 	} else if resp.StatusCode != http.StatusOK {
@@ -171,7 +171,7 @@ func initRules() {
 }
 
 func initData() {
-	b, err := ioutil.ReadFile(internal.Resource("dinosaurs.json"))
+	b, err := os.ReadFile(internal.Resource("dinosaurs.json"))
 	if err != nil {
 		log.Fatalln(err)
 	}
diff --git a/integration/internal/internal.go b/integration/internal/internal.go
index d57b3f91..828f803e 100644
--- a/integration/internal/internal.go
+++ b/integration/internal/internal.go
@@ -18,8 +18,8 @@ package internal
 import (
 	"context"
 	"encoding/json"
-	"io/ioutil"
 	"net/http"
+	"os"
 	"path/filepath"
 	"strings"
 
@@ -52,7 +52,7 @@ func NewTestApp(ctx context.Context, conf *firebase.Config) (*firebase.App, erro
 // APIKey reads the API key string from a file named integration_apikey.txt
 // in the testdata directory.
 func APIKey() (string, error) {
-	b, err := ioutil.ReadFile(Resource(apiKeyPath))
+	b, err := os.ReadFile(Resource(apiKeyPath))
 	if err != nil {
 		return "", err
 	}
@@ -61,7 +61,7 @@ func APIKey() (string, error) {
 
 // ProjectID fetches a Google Cloud project ID for integration tests.
 func ProjectID() (string, error) {
-	b, err := ioutil.ReadFile(Resource(certPath))
+	b, err := os.ReadFile(Resource(certPath))
 	if err != nil {
 		return "", err
 	}
diff --git a/integration/storage/storage_test.go b/integration/storage/storage_test.go
index 860288bc..d641bb97 100644
--- a/integration/storage/storage_test.go
+++ b/integration/storage/storage_test.go
@@ -18,7 +18,7 @@ import (
 	"context"
 	"flag"
 	"fmt"
-	"io/ioutil"
+	"io"
 	"log"
 	"os"
 	"testing"
@@ -115,7 +115,7 @@ func verifyBucket(bucket *gcs.BucketHandle) error {
 		return err
 	}
 	defer r.Close()
-	b, err := ioutil.ReadAll(r)
+	b, err := io.ReadAll(r)
 	if err != nil {
 		return err
 	}
diff --git a/internal/errors_test.go b/internal/errors_test.go
index ccd38f20..d4c41612 100644
--- a/internal/errors_test.go
+++ b/internal/errors_test.go
@@ -19,7 +19,7 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
-	"io/ioutil"
+	"io"
 	"net"
 	"net/http"
 	"net/http/httptest"
@@ -321,7 +321,7 @@ func TestErrorHTTPResponse(t *testing.T) {
 		t.Errorf("Do() Response.StatusCode = %d; want = %d", hr.StatusCode, http.StatusInternalServerError)
 	}
 
-	b, err := ioutil.ReadAll(hr.Body)
+	b, err := io.ReadAll(hr.Body)
 	if err != nil {
 		t.Fatalf("ReadAll(Response.Body) = %v", err)
 	}
diff --git a/internal/http_client.go b/internal/http_client.go
index 9d1257bc..6f70d753 100644
--- a/internal/http_client.go
+++ b/internal/http_client.go
@@ -20,7 +20,6 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"math"
 	"net/http"
 	"runtime"
@@ -121,7 +120,7 @@ func (r *Response) LowLevelResponse() *http.Response {
 	}
 
 	resp := *r.resp
-	resp.Body = ioutil.NopCloser(bytes.NewBuffer(r.Body))
+	resp.Body = io.NopCloser(bytes.NewBuffer(r.Body))
 	return &resp
 }
 
@@ -305,7 +304,7 @@ func (e *jsonEntity) Mime() string {
 
 func newResponse(resp *http.Response) (*Response, error) {
 	defer resp.Body.Close()
-	b, err := ioutil.ReadAll(resp.Body)
+	b, err := io.ReadAll(resp.Body)
 	if err != nil {
 		return nil, err
 	}
diff --git a/internal/http_client_test.go b/internal/http_client_test.go
index 22b498cf..03dccabc 100644
--- a/internal/http_client_test.go
+++ b/internal/http_client_test.go
@@ -18,7 +18,7 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
-	"io/ioutil"
+	"io"
 	"net/http"
 	"net/http/httptest"
 	"reflect"
@@ -147,7 +147,7 @@ func TestHTTPClient(t *testing.T) {
 				t.Errorf("[%d] Content-Type = %q; want = %q", idx, h, "application/json")
 			}
 			wb := []byte(want.body)
-			gb, err := ioutil.ReadAll(r.Body)
+			gb, err := io.ReadAll(r.Body)
 			if err != nil {
 				t.Fatal(err)
 			}
diff --git a/internal/json_http_client_test.go b/internal/json_http_client_test.go
index be827b75..06a503f4 100644
--- a/internal/json_http_client_test.go
+++ b/internal/json_http_client_test.go
@@ -18,7 +18,7 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
-	"io/ioutil"
+	"io"
 	"net/http"
 	"net/http/httptest"
 	"strings"
@@ -72,7 +72,7 @@ func TestDoAndUnmarshalPost(t *testing.T) {
 	var b []byte
 	handler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		req = r
-		b, _ = ioutil.ReadAll(r.Body)
+		b, _ = io.ReadAll(r.Body)
 		resp := `{
 			"name": "test"
 		}`
diff --git a/messaging/messaging_batch.go b/messaging/messaging_batch.go
index 7dc6c110..dcf3af9c 100644
--- a/messaging/messaging_batch.go
+++ b/messaging/messaging_batch.go
@@ -22,7 +22,6 @@ import (
 	"errors"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"mime"
 	"mime/multipart"
 	"net/http"
@@ -466,7 +465,7 @@ func newSendResponse(part *multipart.Part) (*SendResponse, error) {
 		return nil, fmt.Errorf("error parsing multipart body: %v", err)
 	}
 
-	b, err := ioutil.ReadAll(hr.Body)
+	b, err := io.ReadAll(hr.Body)
 	if err != nil {
 		return nil, err
 	}
diff --git a/messaging/messaging_batch_test.go b/messaging/messaging_batch_test.go
index 25ac5a11..f0099d49 100644
--- a/messaging/messaging_batch_test.go
+++ b/messaging/messaging_batch_test.go
@@ -21,7 +21,6 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"mime/multipart"
 	"net/http"
 	"net/http/httptest"
@@ -474,7 +473,7 @@ func TestSendEachInvalidMessage(t *testing.T) {
 
 func TestSendEach(t *testing.T) {
 	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		req, _ := ioutil.ReadAll(r.Body)
+		req, _ := io.ReadAll(r.Body)
 		w.Header().Set("Content-Type", "application/json")
 		for idx, testMessage := range testMessages {
 			if strings.Contains(string(req), testMessage.Topic) {
@@ -502,7 +501,7 @@ func TestSendEach(t *testing.T) {
 
 func TestSendEachDryRun(t *testing.T) {
 	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		req, _ := ioutil.ReadAll(r.Body)
+		req, _ := io.ReadAll(r.Body)
 		w.Header().Set("Content-Type", "application/json")
 		for idx, testMessage := range testMessages {
 			if strings.Contains(string(req), testMessage.Topic) {
@@ -548,7 +547,7 @@ func TestSendEachPartialFailure(t *testing.T) {
 			mu.Lock()
 			serverHitCount++
 			mu.Unlock()
-			reqBody, _ := ioutil.ReadAll(r.Body)
+			reqBody, _ := io.ReadAll(r.Body)
 			var msgIn fcmRequest
 			json.Unmarshal(reqBody, &msgIn)
 
@@ -739,7 +738,7 @@ func TestSendEachForMulticastInvalidMessage(t *testing.T) {
 
 func TestSendEachForMulticast(t *testing.T) {
 	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		req, _ := ioutil.ReadAll(r.Body)
+		req, _ := io.ReadAll(r.Body)
 		w.Header().Set("Content-Type", "application/json")
 		for idx, token := range testMulticastMessage.Tokens {
 			if strings.Contains(string(req), token) {
@@ -767,7 +766,7 @@ func TestSendEachForMulticast(t *testing.T) {
 
 func TestSendEachForMulticastFids(t *testing.T) {
 	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		req, _ := ioutil.ReadAll(r.Body)
+		req, _ := io.ReadAll(r.Body)
 		w.Header().Set("Content-Type", "application/json")
 		for idx, fid := range testFidMulticastMessage.Fids {
 			if strings.Contains(string(req), fid) {
@@ -795,7 +794,7 @@ func TestSendEachForMulticastFids(t *testing.T) {
 
 func TestSendEachForMulticastMixed(t *testing.T) {
 	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		req, _ := ioutil.ReadAll(r.Body)
+		req, _ := io.ReadAll(r.Body)
 		w.Header().Set("Content-Type", "application/json")
 		for idx, token := range testMixedMulticastMessage.Tokens {
 			if strings.Contains(string(req), token) {
@@ -828,7 +827,7 @@ func TestSendEachForMulticastMixed(t *testing.T) {
 
 func TestSendEachForMulticastWithCustomEndpoint(t *testing.T) {
 	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		req, _ := ioutil.ReadAll(r.Body)
+		req, _ := io.ReadAll(r.Body)
 		w.Header().Set("Content-Type", "application/json")
 		for idx, token := range testMulticastMessage.Tokens {
 			if strings.Contains(string(req), token) {
@@ -861,7 +860,7 @@ func TestSendEachForMulticastWithCustomEndpoint(t *testing.T) {
 
 func TestSendEachForMulticastDryRun(t *testing.T) {
 	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		req, _ := ioutil.ReadAll(r.Body)
+		req, _ := io.ReadAll(r.Body)
 		w.Header().Set("Content-Type", "application/json")
 		for idx, token := range testMulticastMessage.Tokens {
 			if strings.Contains(string(req), token) {
@@ -894,7 +893,7 @@ func TestSendEachForMulticastPartialFailure(t *testing.T) {
 
 	var failures []string
 	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		req, _ := ioutil.ReadAll(r.Body)
+		req, _ := io.ReadAll(r.Body)
 
 		for idx, token := range testMulticastMessage.Tokens {
 			if strings.Contains(string(req), token) {
@@ -992,7 +991,7 @@ func TestSendAll(t *testing.T) {
 
 	var req []byte
 	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		req, _ = ioutil.ReadAll(r.Body)
+		req, _ = io.ReadAll(r.Body)
 		w.Header().Set("Content-Type", wantMime)
 		w.Write(resp)
 	}))
@@ -1023,7 +1022,7 @@ func TestSendAllDryRun(t *testing.T) {
 
 	var req []byte
 	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		req, _ = ioutil.ReadAll(r.Body)
+		req, _ = io.ReadAll(r.Body)
 		w.Header().Set("Content-Type", wantMime)
 		w.Write(resp)
 	}))
@@ -1053,7 +1052,7 @@ func TestSendAllPartialFailure(t *testing.T) {
 
 	var req, resp []byte
 	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		req, _ = ioutil.ReadAll(r.Body)
+		req, _ = io.ReadAll(r.Body)
 		w.Header().Set("Content-Type", wantMime)
 		w.Write(resp)
 	}))
@@ -1296,7 +1295,7 @@ func TestSendMulticast(t *testing.T) {
 
 	var req []byte
 	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		req, _ = ioutil.ReadAll(r.Body)
+		req, _ = io.ReadAll(r.Body)
 		w.Header().Set("Content-Type", wantMime)
 		w.Write(resp)
 	}))
@@ -1327,7 +1326,7 @@ func TestSendMulticastWithCustomEndpoint(t *testing.T) {
 
 	var req []byte
 	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		req, _ = ioutil.ReadAll(r.Body)
+		req, _ = io.ReadAll(r.Body)
 		w.Header().Set("Content-Type", wantMime)
 		w.Write(resp)
 	}))
@@ -1367,7 +1366,7 @@ func TestSendMulticastDryRun(t *testing.T) {
 
 	var req []byte
 	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		req, _ = ioutil.ReadAll(r.Body)
+		req, _ = io.ReadAll(r.Body)
 		w.Header().Set("Content-Type", wantMime)
 		w.Write(resp)
 	}))
@@ -1587,7 +1586,7 @@ func checkRequestPart(part *multipart.Part, dryRun bool) error {
 		return fmt.Errorf("X-FIREBASE-CLIENT = %q; want = %q", h, clientVersion)
 	}
 
-	b, _ := ioutil.ReadAll(r.Body)
+	b, _ := io.ReadAll(r.Body)
 	var parsed map[string]interface{}
 	if err := json.Unmarshal(b, &parsed); err != nil {
 		return err
diff --git a/messaging/messaging_test.go b/messaging/messaging_test.go
index 00d4fee9..747a005a 100644
--- a/messaging/messaging_test.go
+++ b/messaging/messaging_test.go
@@ -17,7 +17,7 @@ package messaging
 import (
 	"context"
 	"encoding/json"
-	"io/ioutil"
+	"io"
 	"net/http"
 	"net/http/httptest"
 	"reflect"
@@ -1316,7 +1316,7 @@ func TestSend(t *testing.T) {
 	var b []byte
 	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		tr = r
-		b, _ = ioutil.ReadAll(r.Body)
+		b, _ = io.ReadAll(r.Body)
 		w.Header().Set("Content-Type", "application/json")
 		w.Write([]byte("{ \"name\":\"" + testMessageID + "\" }"))
 	}))
@@ -1345,7 +1345,7 @@ func TestSendWithCustomEndpoint(t *testing.T) {
 	var b []byte
 	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		tr = r
-		b, _ = ioutil.ReadAll(r.Body)
+		b, _ = io.ReadAll(r.Body)
 		w.Header().Set("Content-Type", "application/json")
 		w.Write([]byte("{ \"name\":\"" + testMessageID + "\" }"))
 	}))
@@ -1382,7 +1382,7 @@ func TestSendDryRun(t *testing.T) {
 	var b []byte
 	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		tr = r
-		b, _ = ioutil.ReadAll(r.Body)
+		b, _ = io.ReadAll(r.Body)
 		w.Header().Set("Content-Type", "application/json")
 		w.Write([]byte("{ \"name\":\"" + testMessageID + "\" }"))
 	}))
diff --git a/messaging/topic_mgt_test.go b/messaging/topic_mgt_test.go
index 1b0adba9..c0703022 100644
--- a/messaging/topic_mgt_test.go
+++ b/messaging/topic_mgt_test.go
@@ -17,7 +17,7 @@ package messaging
 import (
 	"context"
 	"encoding/json"
-	"io/ioutil"
+	"io"
 	"net/http"
 	"net/http/httptest"
 	"reflect"
@@ -33,7 +33,7 @@ func TestSubscribe(t *testing.T) {
 	var b []byte
 	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		tr = r
-		b, _ = ioutil.ReadAll(r.Body)
+		b, _ = io.ReadAll(r.Body)
 		w.Header().Set("Content-Type", "application/json")
 		w.Write([]byte("{\"results\": [{}, {\"error\": \"error_reason\"}]}"))
 	}))
@@ -76,7 +76,7 @@ func TestUnsubscribe(t *testing.T) {
 	var b []byte
 	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		tr = r
-		b, _ = ioutil.ReadAll(r.Body)
+		b, _ = io.ReadAll(r.Body)
 		w.Header().Set("Content-Type", "application/json")
 		w.Write([]byte("{\"results\": [{}, {\"error\": \"error_reason\"}]}"))
 	}))
diff --git a/snippets/auth.go b/snippets/auth.go
index a3f8cd8a..11004a9f 100644
--- a/snippets/auth.go
+++ b/snippets/auth.go
@@ -18,7 +18,7 @@ import (
 	"context"
 	"encoding/base64"
 	"encoding/json"
-	"io/ioutil"
+	"io"
 	"log"
 	"net/http"
 	"time"
@@ -809,7 +809,7 @@ func sessionLogoutHandlerWithRevocation(client *auth.Client) http.HandlerFunc {
 }
 
 func getIDTokenFromBody(r *http.Request) (string, error) {
-	b, err := ioutil.ReadAll(r.Body)
+	b, err := io.ReadAll(r.Body)
 	if err != nil {
 		return "", err
 	}