cloud.google.com/go/auth v0.18.2: New2LOTokenProvider

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.New2LOTokenProvider 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.New2LOTokenProvider

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:a07ab2c03b23ce980bc831182c6611a5fb5f76edbcabd344d83fbce2cfd1cec8","contract":["New2LOTokenProvider returns an error when provided with nil Options2LO","New2LOTokenProvider returns an error when required configuration fields are missing","New2LOTokenProvider creates a valid TokenProvider when required fields are supplied","TokenProvider.Token retrieves a valid OAuth2 token using 2LO JWT authorization against a local token server","TokenProvider.Token returns an error when the token server returns an HTTP error response"],"goal":"verify cloud.google.com/go/auth.New2LOTokenProvider 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.New2LOTokenProvider"]},"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.New2LOTokenProvider"],"verifierAdapter":"golang@1"}

module sample

go 1.26.6

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 (
	"crypto/rand"
	"crypto/rsa"
	"crypto/x509"
	"encoding/pem"
	"fmt"
	"log"

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

func main() {
	key, err := rsa.GenerateKey(rand.Reader, 2048)
	if err != nil {
		log.Fatalf("failed to generate RSA key: %v", err)
	}
	keyBytes := pem.EncodeToMemory(&pem.Block{
		Type:  "RSA PRIVATE KEY",
		Bytes: x509.MarshalPKCS1PrivateKey(key),
	})

	opts := &auth.Options2LO{
		Email:      "service-account@example.com",
		PrivateKey: keyBytes,
		TokenURL:   "https://example.com/oauth2/token",
		Scopes:     []string{"https://example.com/auth/read"},
	}

	tp, err := auth.New2LOTokenProvider(opts)
	if err != nil {
		log.Fatalf("failed to create 2LO token provider: %v", err)
	}

	fmt.Printf("Created 2LO token provider: %T\n", tp)
}

{
  "schemaVersion": 1,
  "goal": "verify cloud.google.com/go/auth.New2LOTokenProvider 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.New2LOTokenProvider"
  ]
}

package main

import (
	"context"
	"crypto/rand"
	"crypto/rsa"
	"crypto/x509"
	"encoding/pem"
	"fmt"
	"net/http"
	"net/http/httptest"
	"os"
	"strings"

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

func generateTestKey() ([]byte, error) {
	key, err := rsa.GenerateKey(rand.Reader, 2048)
	if err != nil {
		return nil, fmt.Errorf("failed to generate test key: %w", err)
	}
	return pem.EncodeToMemory(&pem.Block{
		Type:  "RSA PRIVATE KEY",
		Bytes: x509.MarshalPKCS1PrivateKey(key),
	}), nil
}

func main() {
	keyPEM, err := generateTestKey()
	if err != nil {
		fmt.Fprintf(os.Stderr, "Setup failed: %v\n", err)
		os.Exit(1)
	}

	// Assertion 1: New2LOTokenProvider returns an error when provided with nil Options2LO
	{
		tp, err := auth.New2LOTokenProvider(nil)
		if err == nil {
			fmt.Fprintf(os.Stderr, "Assertion 1 failed: expected error for nil options, got provider: %v\n", tp)
			os.Exit(1)
		}
		if !strings.Contains(err.Error(), "options must be provided") {
			fmt.Fprintf(os.Stderr, "Assertion 1 failed: unexpected error message: %v\n", err)
			os.Exit(1)
		}
	}

	// Assertion 2: New2LOTokenProvider returns an error when required configuration fields are missing
	{
		// Missing Email
		if _, err := auth.New2LOTokenProvider(&auth.Options2LO{
			PrivateKey: keyPEM,
			TokenURL:   "https://example.com/token",
		}); err == nil || !strings.Contains(err.Error(), "email must be provided") {
			fmt.Fprintf(os.Stderr, "Assertion 2 failed (missing email): expected error, got %v\n", err)
			os.Exit(1)
		}

		// Missing PrivateKey
		if _, err := auth.New2LOTokenProvider(&auth.Options2LO{
			Email:    "service-account@example.com",
			TokenURL: "https://example.com/token",
		}); err == nil || !strings.Contains(err.Error(), "private key must be provided") {
			fmt.Fprintf(os.Stderr, "Assertion 2 failed (missing private key): expected error, got %v\n", err)
			os.Exit(1)
		}

		// Missing TokenURL
		if _, err := auth.New2LOTokenProvider(&auth.Options2LO{
			Email:      "service-account@example.com",
			PrivateKey: keyPEM,
		}); err == nil || !strings.Contains(err.Error(), "token URL must be provided") {
			fmt.Fprintf(os.Stderr, "Assertion 2 failed (missing token URL): expected error, got %v\n", err)
			os.Exit(1)
		}
	}

	// Assertion 3: New2LOTokenProvider creates a valid TokenProvider when required fields are supplied
	{
		opts := &auth.Options2LO{
			Email:      "service-account@example.com",
			PrivateKey: keyPEM,
			TokenURL:   "https://example.com/token",
		}
		tp, err := auth.New2LOTokenProvider(opts)
		if err != nil {
			fmt.Fprintf(os.Stderr, "Assertion 3 failed: unexpected error: %v\n", err)
			os.Exit(1)
		}
		if tp == nil {
			fmt.Fprintf(os.Stderr, "Assertion 3 failed: expected non-nil TokenProvider\n")
			os.Exit(1)
		}
	}

	// Assertion 4: TokenProvider.Token retrieves a valid OAuth2 token using 2LO JWT authorization against a local token server
	{
		var receivedAssertion string
		var receivedGrantType string
		ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			if r.Method != http.MethodPost {
				http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
				return
			}
			_ = r.ParseForm()
			receivedGrantType = r.Form.Get("grant_type")
			receivedAssertion = r.Form.Get("assertion")

			w.Header().Set("Content-Type", "application/json")
			_, _ = w.Write([]byte(`{
				"access_token": "mock-access-token-xyz123",
				"token_type": "Bearer",
				"expires_in": 3600
			}`))
		}))
		defer ts.Close()

		opts := &auth.Options2LO{
			Email:        "service-account@example.com",
			PrivateKey:   keyPEM,
			PrivateKeyID: "test-key-id",
			TokenURL:     ts.URL,
			Scopes:       []string{"https://example.com/auth/read"},
			Audience:     ts.URL,
		}
		tp, err := auth.New2LOTokenProvider(opts)
		if err != nil {
			fmt.Fprintf(os.Stderr, "Assertion 4 failed: create provider: %v\n", err)
			os.Exit(1)
		}

		tok, err := tp.Token(context.Background())
		if err != nil {
			fmt.Fprintf(os.Stderr, "Assertion 4 failed: fetch token: %v\n", err)
			os.Exit(1)
		}
		if tok == nil {
			fmt.Fprintf(os.Stderr, "Assertion 4 failed: nil token returned\n")
			os.Exit(1)
		}
		if tok.Value != "mock-access-token-xyz123" {
			fmt.Fprintf(os.Stderr, "Assertion 4 failed: expected token value 'mock-access-token-xyz123', got %q\n", tok.Value)
			os.Exit(1)
		}
		if tok.Type != "Bearer" {
			fmt.Fprintf(os.Stderr, "Assertion 4 failed: expected token type 'Bearer', got %q\n", tok.Type)
			os.Exit(1)
		}
		if !tok.IsValid() {
			fmt.Fprintf(os.Stderr, "Assertion 4 failed: expected token to be valid\n")
			os.Exit(1)
		}
		if receivedGrantType != "urn:ietf:params:oauth:grant-type:jwt-bearer" {
			fmt.Fprintf(os.Stderr, "Assertion 4 failed: expected grant_type urn:ietf:params:oauth:grant-type:jwt-bearer, got %q\n", receivedGrantType)
			os.Exit(1)
		}
		if receivedAssertion == "" {
			fmt.Fprintf(os.Stderr, "Assertion 4 failed: expected non-empty JWT assertion\n")
			os.Exit(1)
		}
	}

	// Assertion 5: TokenProvider.Token returns an error when the token server returns an HTTP error response
	{
		ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			w.Header().Set("Content-Type", "application/json")
			w.WriteHeader(http.StatusBadRequest)
			_, _ = w.Write([]byte(`{"error": "invalid_grant"}`))
		}))
		defer ts.Close()

		opts := &auth.Options2LO{
			Email:      "service-account@example.com",
			PrivateKey: keyPEM,
			TokenURL:   ts.URL,
		}
		tp, err := auth.New2LOTokenProvider(opts)
		if err != nil {
			fmt.Fprintf(os.Stderr, "Assertion 5 failed: create provider: %v\n", err)
			os.Exit(1)
		}

		_, err = tp.Token(context.Background())
		if err == nil {
			fmt.Fprintf(os.Stderr, "Assertion 5 failed: expected error on 400 Bad Request, got nil\n")
			os.Exit(1)
		}
	}

	fmt.Println("PASS: all New2LOTokenProvider contract assertions passed")
}