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

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.Style 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.Style

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:sha256:532f5ae2cccefc182b7225a6a90217280a1608f73f34595da173a3c7f672375c","contract":["auth.Style is an integer type representing OAuth 2.0 client authentication styles","auth.Style zero-value is auth.StyleUnknown","auth.Style constants StyleUnknown, StyleInParams, and StyleInHeader are distinct","auth.Options3LO uses auth.Style in its AuthStyle field and defaults to StyleUnknown","auth.New3LOTokenProvider accepts auth.StyleInParams and auth.StyleInHeader, but rejects auth.StyleUnknown"],"goal":"verify cloud.google.com/go/auth.Style 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.Style"]},"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.Style"],"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 sample

import (
	"errors"

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

// ValidateAuthStyle checks if the provided Style is supported and configured.
// It returns an error if the style is StyleUnknown or an unrecognized value.
func ValidateAuthStyle(s auth.Style) error {
	switch s {
	case auth.StyleInParams, auth.StyleInHeader:
		return nil
	case auth.StyleUnknown:
		return errors.New("auth: auth style must be provided")
	default:
		return errors.New("auth: unknown auth style")
	}
}

// New3LOOptions creates an Options3LO struct configured with the given auth.Style.
func New3LOOptions(clientID, clientSecret, authURL, tokenURL, refreshToken string, style auth.Style) *auth.Options3LO {
	return &auth.Options3LO{
		ClientID:     clientID,
		ClientSecret: clientSecret,
		AuthURL:      authURL,
		TokenURL:     tokenURL,
		AuthStyle:    style,
		RefreshToken: refreshToken,
	}
}

// CreateTokenProvider creates a TokenProvider from the given options.
func CreateTokenProvider(opts *auth.Options3LO) (auth.TokenProvider, error) {
	return auth.New3LOTokenProvider(opts)
}

{
  "schemaVersion": 1,
  "goal": "verify cloud.google.com/go/auth.Style 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.Style"
  ]
}

package main

import (
	"fmt"
	"os"
	"strings"

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

func main() {
	if err := runContractTests(); err != nil {
		fmt.Fprintf(os.Stderr, "Contract test failed: %v\n", err)
		os.Exit(1)
	}
	fmt.Println("PASS: cloud.google.com/go/auth.Style contract verified")
}

func runContractTests() error {
	// Assertion 1: auth.Style is an integer type representing OAuth 2.0 client authentication styles
	var s0, s1, s2 auth.Style = auth.Style(0), auth.Style(1), auth.Style(2)
	if s0 != auth.StyleUnknown {
		return fmt.Errorf("expected auth.Style(0) == StyleUnknown, got %v", s0)
	}
	if s1 != auth.StyleInParams {
		return fmt.Errorf("expected auth.Style(1) == StyleInParams, got %v", s1)
	}
	if s2 != auth.StyleInHeader {
		return fmt.Errorf("expected auth.Style(2) == StyleInHeader, got %v", s2)
	}

	// Assertion 2: auth.Style zero-value is auth.StyleUnknown
	var defaultStyle auth.Style
	if defaultStyle != auth.StyleUnknown {
		return fmt.Errorf("expected zero-valued auth.Style to be StyleUnknown, got %v", defaultStyle)
	}

	// Assertion 3: auth.Style constants StyleUnknown, StyleInParams, and StyleInHeader are distinct
	if auth.StyleUnknown == auth.StyleInParams {
		return fmt.Errorf("auth.StyleUnknown equals auth.StyleInParams")
	}
	if auth.StyleUnknown == auth.StyleInHeader {
		return fmt.Errorf("auth.StyleUnknown equals auth.StyleInHeader")
	}
	if auth.StyleInParams == auth.StyleInHeader {
		return fmt.Errorf("auth.StyleInParams equals auth.StyleInHeader")
	}

	// Assertion 4: auth.Options3LO uses auth.Style in its AuthStyle field and defaults to StyleUnknown
	defaultOpts := &auth.Options3LO{}
	if defaultOpts.AuthStyle != auth.StyleUnknown {
		return fmt.Errorf("expected default Options3LO.AuthStyle to be StyleUnknown, got %v", defaultOpts.AuthStyle)
	}
	if err := sample.ValidateAuthStyle(defaultOpts.AuthStyle); err == nil {
		return fmt.Errorf("expected ValidateAuthStyle to reject default StyleUnknown")
	}

	// Assertion 5: auth.New3LOTokenProvider accepts auth.StyleInParams and auth.StyleInHeader, but rejects auth.StyleUnknown
	optsUnknown := sample.New3LOOptions("client-id", "client-secret", "http://localhost/auth", "http://localhost/token", "refresh-token", auth.StyleUnknown)
	tpUnknown, err := sample.CreateTokenProvider(optsUnknown)
	if err == nil {
		return fmt.Errorf("expected New3LOTokenProvider to fail with StyleUnknown, got provider: %v", tpUnknown)
	}
	if !strings.Contains(err.Error(), "auth style must be provided") {
		return fmt.Errorf("expected 'auth style must be provided' error, got: %v", err)
	}

	optsParams := sample.New3LOOptions("client-id", "client-secret", "http://localhost/auth", "http://localhost/token", "refresh-token", auth.StyleInParams)
	if err := sample.ValidateAuthStyle(optsParams.AuthStyle); err != nil {
		return fmt.Errorf("ValidateAuthStyle rejected StyleInParams: %w", err)
	}
	tpParams, err := sample.CreateTokenProvider(optsParams)
	if err != nil {
		return fmt.Errorf("failed to create TokenProvider with StyleInParams: %w", err)
	}
	if tpParams == nil {
		return fmt.Errorf("expected non-nil TokenProvider with StyleInParams")
	}

	optsHeader := sample.New3LOOptions("client-id", "client-secret", "http://localhost/auth", "http://localhost/token", "refresh-token", auth.StyleInHeader)
	if err := sample.ValidateAuthStyle(optsHeader.AuthStyle); err != nil {
		return fmt.Errorf("ValidateAuthStyle rejected StyleInHeader: %w", err)
	}
	tpHeader, err := sample.CreateTokenProvider(optsHeader)
	if err != nil {
		return fmt.Errorf("failed to create TokenProvider with StyleInHeader: %w", err)
	}
	if tpHeader == nil {
		return fmt.Errorf("expected non-nil TokenProvider with StyleInHeader")
	}

	return nil
}