cloud.google.com/go/auth v0.18.2: NewCachedTokenProvider

Clean-room public code sample — generation instructions

Write a brand-new, minimal, self-contained code sample in this clean-room directory.
Do not copy, paraphrase, or reference any existing project source. Work only from this spec.

A csx.json manifest scaffold already exists. Do not recreate it from memory. Preserve its case.goal, packages and symbols; fill its empty case.contract with exact assertions and correct its environment, commands and verifierAdapter for the files you generate.

Goal: verify cloud.google.com/go/auth.NewCachedTokenProvider in pkg:golang/cloud.google.com/go/auth@v0.18.2
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/cloud.google.com/go/auth@v0.18.2
Demonstrate these symbols/APIs:
  - cloud.google.com/go/auth.NewCachedTokenProvider

Rules:
  - One focused purpose; the smallest project that proves the goal.
  - Include a contract test (test/contract.*) that runs OFFLINE and exits 0 exactly when the goal behavior works.
  - Pin every dependency with a lockfile so resolution is reproducible.
  - No secrets, credentials, or tokens. No real URLs (only example.com or localhost). No absolute paths.
  - No personal names, emails, company names, or project identifiers of any kind.
  - No binaries and no generated output (node_modules, dist, target, venv, .git, .env).
  - Keep it under 200 files and 256KB packed.

{"case":{"caseId":"case:sha256:cc97234857dab157b7caf31459779152ed392c5c655c5ce4fa89e1f997a9add4","contract":["NewCachedTokenProvider wraps a TokenProvider and caches valid tokens across calls","NewCachedTokenProvider returns the same provider instance if already cached","NewCachedTokenProvider refreshes an expired token when DisableAsyncRefresh is true","NewCachedTokenProvider with DisableAutoRefresh preserves and returns cached token even after expiry","NewCachedTokenProvider propagates errors from the underlying TokenProvider"],"goal":"verify cloud.google.com/go/auth.NewCachedTokenProvider in pkg:golang/cloud.google.com/go/auth@v0.18.2","kind":"HOW","packages":["pkg:golang/cloud.google.com/go/auth@v0.18.2"],"schemaVersion":1,"symbols":["cloud.google.com/go/auth.NewCachedTokenProvider"]},"contractCommand":["go","run","./test"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"golang","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"go","schemaVersion":1},"license":"MIT-0","packages":["pkg:golang/cloud.google.com/go/auth@v0.18.2"],"schemaVersion":1,"subject":"pkg:golang/cloud.google.com/go/auth@v0.18.2","symbols":["cloud.google.com/go/auth.NewCachedTokenProvider"],"verifierAdapter":"golang@1"}

module sample

go 1.24.0

require cloud.google.com/go/auth v0.18.2

require (
	cloud.google.com/go/compute/metadata v0.9.0 // indirect
	github.com/googleapis/gax-go/v2 v2.17.0 // indirect
	golang.org/x/sys v0.40.0 // indirect
)

cloud.google.com/go/auth v0.18.2 h1:+Nbt5Ev0xEqxlNjd6c+yYUeosQ5TtEUaNcN/3FozlaM=
cloud.google.com/go/auth v0.18.2/go.mod h1:xD+oY7gcahcu7G2SG2DsBerfFxgPAJz17zz2joOFF3M=
cloud.google.com/go/compute/metadata v0.9.0 h1:pDUj4QMoPejqq20dK0Pg2N4yG9zIkYGdBtwLoEkH9Zs=
cloud.google.com/go/compute/metadata v0.9.0/go.mod h1:E0bWwX5wTnLPedCKqk3pJmVgCBSM6qQI1yTBdEb3C10=
github.com/cespare/xxhash/v2 v2.3.0 h1:UL815xU9SqsFlibzuggzjXhog7bL6oX9BbNZnL2UFvs=
github.com/cespare/xxhash/v2 v2.3.0/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XLFGgcrjCOs=
github.com/felixge/httpsnoop v1.0.4 h1:NFTV2Zj1bL4mc9sqWACXbQFVBBg2W3GPvqp8/ESS2Wg=
github.com/felixge/httpsnoop v1.0.4/go.mod h1:m8KPJKqk1gH5J9DgRY2ASl2lWCfGKXixSwevea8zH2U=
github.com/go-logr/logr v1.4.3 h1:CjnDlHq8ikf6E492q6eKboGOC0T8CDaOvkHCIg8idEI=
github.com/go-logr/logr v1.4.3/go.mod h1:9T104GzyrTigFIr8wt5mBrctHMim0Nb2HLGrmQ40KvY=
github.com/go-logr/stdr v1.2.2 h1:hSWxHoqTgW2S2qGc0LTAI563KZ5YKYRhT3MFKZMbjag=
github.com/go-logr/stdr v1.2.2/go.mod h1:mMo/vtBO5dYbehREoey6XUKy/eSumjCCveDpRre4VKE=
github.com/google/go-cmp v0.7.0 h1:wk8382ETsv4JYUZwIsn6YpYiWiBsYLSJiTsyBybVuN8=
github.com/google/go-cmp v0.7.0/go.mod h1:pXiqmnSA92OHEEa9HXL2W4E7lf9JzCmGVUdgjX3N/iU=
github.com/google/s2a-go v0.1.9 h1:LGD7gtMgezd8a/Xak7mEWL0PjoTQFvpRudN895yqKW0=
github.com/google/s2a-go v0.1.9/go.mod h1:YA0Ei2ZQL3acow2O62kdp9UlnvMmU7kA6Eutn0dXayM=
github.com/googleapis/enterprise-certificate-proxy v0.3.11 h1:vAe81Msw+8tKUxi2Dqh/NZMz7475yUvmRIkXr4oN2ao=
github.com/googleapis/enterprise-certificate-proxy v0.3.11/go.mod h1:RFV7MUdlb7AgEq2v7FmMCfeSMCllAzWxFgRdusoGks8=
github.com/googleapis/gax-go/v2 v2.17.0 h1:RksgfBpxqff0EZkDWYuz9q/uWsTVz+kf43LsZ1J6SMc=
github.com/googleapis/gax-go/v2 v2.17.0/go.mod h1:mzaqghpQp4JDh3HvADwrat+6M3MOIDp5YKHhb9PAgDY=
go.opentelemetry.io/auto/sdk v1.2.1 h1:jXsnJ4Lmnqd11kwkBV2LgLoFMZKizbCi5fNZ/ipaZ64=
go.opentelemetry.io/auto/sdk v1.2.1/go.mod h1:KRTj+aOaElaLi+wW1kO/DZRXwkF4C5xPbEe3ZiIhN7Y=
go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.61.0 h1:F7Jx+6hwnZ41NSFTO5q4LYDtJRXBf2PD0rNBkeB/lus=
go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.61.0/go.mod h1:UHB22Z8QsdRDrnAtX4PntOl36ajSxcdUMt1sF7Y6E7Q=
go.opentelemetry.io/otel v1.39.0 h1:8yPrr/S0ND9QEfTfdP9V+SiwT4E0G7Y5MO7p85nis48=
go.opentelemetry.io/otel v1.39.0/go.mod h1:kLlFTywNWrFyEdH0oj2xK0bFYZtHRYUdv1NklR/tgc8=
go.opentelemetry.io/otel/metric v1.39.0 h1:d1UzonvEZriVfpNKEVmHXbdf909uGTOQjA0HF0Ls5Q0=
go.opentelemetry.io/otel/metric v1.39.0/go.mod h1:jrZSWL33sD7bBxg1xjrqyDjnuzTUB0x1nBERXd7Ftcs=
go.opentelemetry.io/otel/trace v1.39.0 h1:2d2vfpEDmCJ5zVYz7ijaJdOF59xLomrvj7bjt6/qCJI=
go.opentelemetry.io/otel/trace v1.39.0/go.mod h1:88w4/PnZSazkGzz/w84VHpQafiU4EtqqlVdxWy+rNOA=
golang.org/x/crypto v0.47.0 h1:V6e3FRj+n4dbpw86FJ8Fv7XVOql7TEwpHapKoMJ/GO8=
golang.org/x/crypto v0.47.0/go.mod h1:ff3Y9VzzKbwSSEzWqJsJVBnWmRwRSHt/6Op5n9bQc4A=
golang.org/x/net v0.49.0 h1:eeHFmOGUTtaaPSGNmjBKpbng9MulQsJURQUAfUwY++o=
golang.org/x/net v0.49.0/go.mod h1:/ysNB2EvaqvesRkuLAyjI1ycPZlQHM3q01F02UY/MV8=
golang.org/x/sys v0.40.0 h1:DBZZqJ2Rkml6QMQsZywtnjnnGvHza6BTfYFWY9kjEWQ=
golang.org/x/sys v0.40.0/go.mod h1:OgkHotnGiDImocRcuBABYBEXf8A9a87e/uXjp9XT3ks=
golang.org/x/text v0.33.0 h1:B3njUFyqtHDUI5jMn1YIr5B0IE2U0qck04r6d4KPAxE=
golang.org/x/text v0.33.0/go.mod h1:LuMebE6+rBincTi9+xWTY8TztLzKHc/9C1uBCG27+q8=
google.golang.org/genproto v0.0.0-20260128011058-8636f8732409 h1:VQZ/yAbAtjkHgH80teYd2em3xtIkkHd7ZhqfH2N9CsM=
google.golang.org/genproto/googleapis/rpc v0.0.0-20260128011058-8636f8732409 h1:H86B94AW+VfJWDqFeEbBPhEtHzJwJfTbgE2lZa54ZAQ=
google.golang.org/genproto/googleapis/rpc v0.0.0-20260128011058-8636f8732409/go.mod h1:j9x/tPzZkyxcgEFkiKEEGxfvyumM01BEtsW8xzOahRQ=
google.golang.org/grpc v1.78.0 h1:K1XZG/yGDJnzMdd/uZHAkVqJE+xIDOcmdSFZkBUicNc=
google.golang.org/grpc v1.78.0/go.mod h1:I47qjTo4OKbMkjA/aOOwxDIiPSBofUtQUI5EfpWvW7U=
google.golang.org/protobuf v1.36.11 h1:fV6ZwhNocDyBLK0dj+fg8ektcVegBBuEolpbTQyBNVE=
google.golang.org/protobuf v1.36.11/go.mod h1:HTf+CrKn2C3g5S8VImy6tdcUvCska2kB7j23XfzDpco=

package main

import (
	"context"
	"fmt"
	"time"

	"cloud.google.com/go/auth"
)

type customTokenProvider struct {
	count int
}

func (p *customTokenProvider) Token(ctx context.Context) (*auth.Token, error) {
	p.count++
	return &auth.Token{
		Value:  fmt.Sprintf("sample-token-%d", p.count),
		Type:   "Bearer",
		Expiry: time.Now().Add(1 * time.Hour),
	}, nil
}

func main() {
	ctx := context.Background()
	rawProvider := &customTokenProvider{}
	cachedProvider := auth.NewCachedTokenProvider(rawProvider, nil)

	// Fetch token first time: underlying provider is called
	tok1, err := cachedProvider.Token(ctx)
	if err != nil {
		panic(err)
	}
	fmt.Printf("First token: %s (underlying calls: %d)\n", tok1.Value, rawProvider.count)

	// Fetch token second time: cached token is returned without calling provider
	tok2, err := cachedProvider.Token(ctx)
	if err != nil {
		panic(err)
	}
	fmt.Printf("Second token: %s (underlying calls: %d)\n", tok2.Value, rawProvider.count)
}

{
  "schemaVersion": 1,
  "goal": "verify cloud.google.com/go/auth.NewCachedTokenProvider in pkg:golang/cloud.google.com/go/auth@v0.18.2",
  "kind": "HOW",
  "packages": [
    "pkg:golang/cloud.google.com/go/auth@v0.18.2"
  ],
  "symbols": [
    "cloud.google.com/go/auth.NewCachedTokenProvider"
  ]
}

package main

import (
	"context"
	"errors"
	"fmt"
	"os"
	"sync"
	"time"

	"cloud.google.com/go/auth"
)

type mockProvider struct {
	mu     sync.Mutex
	calls  int
	tokens []*auth.Token
	errs   []error
}

func (m *mockProvider) Token(ctx context.Context) (*auth.Token, error) {
	m.mu.Lock()
	defer m.mu.Unlock()
	idx := m.calls
	m.calls++
	if idx < len(m.errs) && m.errs[idx] != nil {
		return nil, m.errs[idx]
	}
	if idx < len(m.tokens) {
		return m.tokens[idx], nil
	}
	return &auth.Token{Value: "default-val", Expiry: time.Now().Add(1 * time.Hour)}, nil
}

func main() {
	ctx := context.Background()

	// Assertion 1: NewCachedTokenProvider wraps a TokenProvider and caches valid tokens across calls
	{
		tok := &auth.Token{
			Value:  "tok-val-1",
			Type:   "Bearer",
			Expiry: time.Now().Add(1 * time.Hour),
		}
		mock := &mockProvider{tokens: []*auth.Token{tok}}
		cached := auth.NewCachedTokenProvider(mock, nil)

		t1, err := cached.Token(ctx)
		if err != nil {
			fmt.Fprintf(os.Stderr, "FAIL assertion 1: unexpected error on t1: %v\n", err)
			os.Exit(1)
		}
		if t1.Value != "tok-val-1" {
			fmt.Fprintf(os.Stderr, "FAIL assertion 1: got value %q, want %q\n", t1.Value, "tok-val-1")
			os.Exit(1)
		}

		t2, err := cached.Token(ctx)
		if err != nil {
			fmt.Fprintf(os.Stderr, "FAIL assertion 1: unexpected error on t2: %v\n", err)
			os.Exit(1)
		}
		if t2.Value != "tok-val-1" {
			fmt.Fprintf(os.Stderr, "FAIL assertion 1: got value %q, want %q\n", t2.Value, "tok-val-1")
			os.Exit(1)
		}
		if mock.calls != 1 {
			fmt.Fprintf(os.Stderr, "FAIL assertion 1: expected 1 call, got %d\n", mock.calls)
			os.Exit(1)
		}
	}

	// Assertion 2: NewCachedTokenProvider returns the same provider instance if already cached
	{
		mock := &mockProvider{}
		cached1 := auth.NewCachedTokenProvider(mock, nil)
		cached2 := auth.NewCachedTokenProvider(cached1, nil)
		if cached1 != cached2 {
			fmt.Fprintf(os.Stderr, "FAIL assertion 2: expected idempotent wrapper to return identical instance\n")
			os.Exit(1)
		}
	}

	// Assertion 3: NewCachedTokenProvider refreshes an expired token when DisableAsyncRefresh is true
	{
		expiredTok := &auth.Token{
			Value:  "expired-val",
			Type:   "Bearer",
			Expiry: time.Now().Add(-10 * time.Minute),
		}
		freshTok := &auth.Token{
			Value:  "fresh-val",
			Type:   "Bearer",
			Expiry: time.Now().Add(1 * time.Hour),
		}
		mock := &mockProvider{tokens: []*auth.Token{expiredTok, freshTok}}
		opts := &auth.CachedTokenProviderOptions{
			DisableAsyncRefresh: true,
		}
		cached := auth.NewCachedTokenProvider(mock, opts)

		t1, err := cached.Token(ctx)
		if err != nil {
			fmt.Fprintf(os.Stderr, "FAIL assertion 3: unexpected error on t1: %v\n", err)
			os.Exit(1)
		}
		if t1.Value != "expired-val" {
			fmt.Fprintf(os.Stderr, "FAIL assertion 3: got %q, want %q\n", t1.Value, "expired-val")
			os.Exit(1)
		}

		// Second call should detect expired token and perform blocking refresh to fetch freshTok
		t2, err := cached.Token(ctx)
		if err != nil {
			fmt.Fprintf(os.Stderr, "FAIL assertion 3: unexpected error on t2: %v\n", err)
			os.Exit(1)
		}
		if t2.Value != "fresh-val" {
			fmt.Fprintf(os.Stderr, "FAIL assertion 3: got %q, want %q\n", t2.Value, "fresh-val")
			os.Exit(1)
		}
		if mock.calls != 2 {
			fmt.Fprintf(os.Stderr, "FAIL assertion 3: expected 2 calls, got %d\n", mock.calls)
			os.Exit(1)
		}
	}

	// Assertion 4: NewCachedTokenProvider with DisableAutoRefresh preserves and returns cached token even after expiry
	{
		expiredTok := &auth.Token{
			Value:  "fixed-val",
			Type:   "Bearer",
			Expiry: time.Now().Add(-10 * time.Minute),
		}
		freshTok := &auth.Token{
			Value:  "ignored-val",
			Type:   "Bearer",
			Expiry: time.Now().Add(1 * time.Hour),
		}
		mock := &mockProvider{tokens: []*auth.Token{expiredTok, freshTok}}
		opts := &auth.CachedTokenProviderOptions{
			DisableAutoRefresh: true,
		}
		cached := auth.NewCachedTokenProvider(mock, opts)

		t1, err := cached.Token(ctx)
		if err != nil {
			fmt.Fprintf(os.Stderr, "FAIL assertion 4: unexpected error on t1: %v\n", err)
			os.Exit(1)
		}
		t2, err := cached.Token(ctx)
		if err != nil {
			fmt.Fprintf(os.Stderr, "FAIL assertion 4: unexpected error on t2: %v\n", err)
			os.Exit(1)
		}
		if t1.Value != "fixed-val" || t2.Value != "fixed-val" {
			fmt.Fprintf(os.Stderr, "FAIL assertion 4: tokens did not match fixed value\n")
			os.Exit(1)
		}
		if mock.calls != 1 {
			fmt.Fprintf(os.Stderr, "FAIL assertion 4: expected 1 call with DisableAutoRefresh, got %d\n", mock.calls)
			os.Exit(1)
		}
	}

	// Assertion 5: NewCachedTokenProvider propagates errors from the underlying TokenProvider
	{
		testErr := errors.New("underlying provider failure")
		mock := &mockProvider{errs: []error{testErr}}
		cached := auth.NewCachedTokenProvider(mock, nil)

		_, err := cached.Token(ctx)
		if err == nil {
			fmt.Fprintf(os.Stderr, "FAIL assertion 5: expected error, got nil\n")
			os.Exit(1)
		}
		if !errors.Is(err, testErr) {
			fmt.Fprintf(os.Stderr, "FAIL assertion 5: expected error %v, got %v\n", testErr, err)
			os.Exit(1)
		}
	}

	fmt.Println("All NewCachedTokenProvider contract assertions passed.")
}