feat: add external authorization service (authzd) with JWT authentication

- Add new authzd gRPC service implementing Envoy's external authorization API
- Integrate JWT authentication filter in Envoy configuration with claim extraction
- Update middleware to support both cookie-based and header-based user authentication
- Add comprehensive test coverage for authorization service and server
- Configure proper service orchestration with authzd, sparkled, and Envoy
- Update build system and Docker configuration for multi-service deployment
- Add grpcurl tool for gRPC service debugging and testing

This enables fine-grained authorization control through Envoy's ext_authz filter
while maintaining backward compatibility with existing cookie-based authentication.

10 files changed, 1553 insertions, 0 deletions

diff --git a/vendor/cloud.google.com/go/compute/metadata/CHANGES.md b/vendor/cloud.google.com/go/compute/metadata/CHANGES.md
new file mode 100644
index 0000000..bcfb5d8
--- /dev/null
+++ b/vendor/cloud.google.com/go/compute/metadata/CHANGES.md
@@ -0,0 +1,66 @@
+# Changes
+
+## [0.6.0](https://github.com/googleapis/google-cloud-go/compare/compute/metadata/v0.5.2...compute/metadata/v0.6.0) (2024-12-13)
+
+
+### Features
+
+* **compute/metadata:** Add debug logging ([#11078](https://github.com/googleapis/google-cloud-go/issues/11078)) ([a816814](https://github.com/googleapis/google-cloud-go/commit/a81681463906e4473570a2f426eb0dc2de64e53f))
+
+## [0.5.2](https://github.com/googleapis/google-cloud-go/compare/compute/metadata/v0.5.1...compute/metadata/v0.5.2) (2024-09-20)
+
+
+### Bug Fixes
+
+* **compute/metadata:** Close Response Body for failed request ([#10891](https://github.com/googleapis/google-cloud-go/issues/10891)) ([e91d45e](https://github.com/googleapis/google-cloud-go/commit/e91d45e4757a9e354114509ba9800085d9e0ff1f))
+
+## [0.5.1](https://github.com/googleapis/google-cloud-go/compare/compute/metadata/v0.5.0...compute/metadata/v0.5.1) (2024-09-12)
+
+
+### Bug Fixes
+
+* **compute/metadata:** Check error chain for retryable error ([#10840](https://github.com/googleapis/google-cloud-go/issues/10840)) ([2bdedef](https://github.com/googleapis/google-cloud-go/commit/2bdedeff621b223d63cebc4355fcf83bc68412cd))
+
+## [0.5.0](https://github.com/googleapis/google-cloud-go/compare/compute/metadata/v0.4.0...compute/metadata/v0.5.0) (2024-07-10)
+
+
+### Features
+
+* **compute/metadata:** Add sys check for windows OnGCE ([#10521](https://github.com/googleapis/google-cloud-go/issues/10521)) ([3b9a830](https://github.com/googleapis/google-cloud-go/commit/3b9a83063960d2a2ac20beb47cc15818a68bd302))
+
+## [0.4.0](https://github.com/googleapis/google-cloud-go/compare/compute/metadata/v0.3.0...compute/metadata/v0.4.0) (2024-07-01)
+
+
+### Features
+
+* **compute/metadata:** Add context for all functions/methods ([#10370](https://github.com/googleapis/google-cloud-go/issues/10370)) ([66b8efe](https://github.com/googleapis/google-cloud-go/commit/66b8efe7ad877e052b2987bb4475477e38c67bb3))
+
+
+### Documentation
+
+* **compute/metadata:** Update OnGCE description ([#10408](https://github.com/googleapis/google-cloud-go/issues/10408)) ([6a46dca](https://github.com/googleapis/google-cloud-go/commit/6a46dca4eae4f88ec6f88822e01e5bf8aeca787f))
+
+## [0.3.0](https://github.com/googleapis/google-cloud-go/compare/compute/metadata/v0.2.3...compute/metadata/v0.3.0) (2024-04-15)
+
+
+### Features
+
+* **compute/metadata:** Add context aware functions  ([#9733](https://github.com/googleapis/google-cloud-go/issues/9733)) ([e4eb5b4](https://github.com/googleapis/google-cloud-go/commit/e4eb5b46ee2aec9d2fc18300bfd66015e25a0510))
+
+## [0.2.3](https://github.com/googleapis/google-cloud-go/compare/compute/metadata/v0.2.2...compute/metadata/v0.2.3) (2022-12-15)
+
+
+### Bug Fixes
+
+* **compute/metadata:** Switch DNS lookup to an absolute lookup ([119b410](https://github.com/googleapis/google-cloud-go/commit/119b41060c7895e45e48aee5621ad35607c4d021)), refs [#7165](https://github.com/googleapis/google-cloud-go/issues/7165)
+
+## [0.2.2](https://github.com/googleapis/google-cloud-go/compare/compute/metadata/v0.2.1...compute/metadata/v0.2.2) (2022-12-01)
+
+
+### Bug Fixes
+
+* **compute/metadata:** Set IdleConnTimeout for http.Client ([#7084](https://github.com/googleapis/google-cloud-go/issues/7084)) ([766516a](https://github.com/googleapis/google-cloud-go/commit/766516aaf3816bfb3159efeea65aa3d1d205a3e2)), refs [#5430](https://github.com/googleapis/google-cloud-go/issues/5430)
+
+## [0.1.0] (2022-10-26)
+
+Initial release of metadata being it's own module.
diff --git a/vendor/cloud.google.com/go/compute/metadata/LICENSE b/vendor/cloud.google.com/go/compute/metadata/LICENSE
new file mode 100644
index 0000000..d645695
--- /dev/null
+++ b/vendor/cloud.google.com/go/compute/metadata/LICENSE
@@ -0,0 +1,202 @@
+
+                                 Apache License
+                           Version 2.0, January 2004
+                        http://www.apache.org/licenses/
+
+   TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
+
+   1. Definitions.
+
+      "License" shall mean the terms and conditions for use, reproduction,
+      and distribution as defined by Sections 1 through 9 of this document.
+
+      "Licensor" shall mean the copyright owner or entity authorized by
+      the copyright owner that is granting the License.
+
+      "Legal Entity" shall mean the union of the acting entity and all
+      other entities that control, are controlled by, or are under common
+      control with that entity. For the purposes of this definition,
+      "control" means (i) the power, direct or indirect, to cause the
+      direction or management of such entity, whether by contract or
+      otherwise, or (ii) ownership of fifty percent (50%) or more of the
+      outstanding shares, or (iii) beneficial ownership of such entity.
+
+      "You" (or "Your") shall mean an individual or Legal Entity
+      exercising permissions granted by this License.
+
+      "Source" form shall mean the preferred form for making modifications,
+      including but not limited to software source code, documentation
+      source, and configuration files.
+
+      "Object" form shall mean any form resulting from mechanical
+      transformation or translation of a Source form, including but
+      not limited to compiled object code, generated documentation,
+      and conversions to other media types.
+
+      "Work" shall mean the work of authorship, whether in Source or
+      Object form, made available under the License, as indicated by a
+      copyright notice that is included in or attached to the work
+      (an example is provided in the Appendix below).
+
+      "Derivative Works" shall mean any work, whether in Source or Object
+      form, that is based on (or derived from) the Work and for which the
+      editorial revisions, annotations, elaborations, or other modifications
+      represent, as a whole, an original work of authorship. For the purposes
+      of this License, Derivative Works shall not include works that remain
+      separable from, or merely link (or bind by name) to the interfaces of,
+      the Work and Derivative Works thereof.
+
+      "Contribution" shall mean any work of authorship, including
+      the original version of the Work and any modifications or additions
+      to that Work or Derivative Works thereof, that is intentionally
+      submitted to Licensor for inclusion in the Work by the copyright owner
+      or by an individual or Legal Entity authorized to submit on behalf of
+      the copyright owner. For the purposes of this definition, "submitted"
+      means any form of electronic, verbal, or written communication sent
+      to the Licensor or its representatives, including but not limited to
+      communication on electronic mailing lists, source code control systems,
+      and issue tracking systems that are managed by, or on behalf of, the
+      Licensor for the purpose of discussing and improving the Work, but
+      excluding communication that is conspicuously marked or otherwise
+      designated in writing by the copyright owner as "Not a Contribution."
+
+      "Contributor" shall mean Licensor and any individual or Legal Entity
+      on behalf of whom a Contribution has been received by Licensor and
+      subsequently incorporated within the Work.
+
+   2. Grant of Copyright License. Subject to the terms and conditions of
+      this License, each Contributor hereby grants to You a perpetual,
+      worldwide, non-exclusive, no-charge, royalty-free, irrevocable
+      copyright license to reproduce, prepare Derivative Works of,
+      publicly display, publicly perform, sublicense, and distribute the
+      Work and such Derivative Works in Source or Object form.
+
+   3. Grant of Patent License. Subject to the terms and conditions of
+      this License, each Contributor hereby grants to You a perpetual,
+      worldwide, non-exclusive, no-charge, royalty-free, irrevocable
+      (except as stated in this section) patent license to make, have made,
+      use, offer to sell, sell, import, and otherwise transfer the Work,
+      where such license applies only to those patent claims licensable
+      by such Contributor that are necessarily infringed by their
+      Contribution(s) alone or by combination of their Contribution(s)
+      with the Work to which such Contribution(s) was submitted. If You
+      institute patent litigation against any entity (including a
+      cross-claim or counterclaim in a lawsuit) alleging that the Work
+      or a Contribution incorporated within the Work constitutes direct
+      or contributory patent infringement, then any patent licenses
+      granted to You under this License for that Work shall terminate
+      as of the date such litigation is filed.
+
+   4. Redistribution. You may reproduce and distribute copies of the
+      Work or Derivative Works thereof in any medium, with or without
+      modifications, and in Source or Object form, provided that You
+      meet the following conditions:
+
+      (a) You must give any other recipients of the Work or
+          Derivative Works a copy of this License; and
+
+      (b) You must cause any modified files to carry prominent notices
+          stating that You changed the files; and
+
+      (c) You must retain, in the Source form of any Derivative Works
+          that You distribute, all copyright, patent, trademark, and
+          attribution notices from the Source form of the Work,
+          excluding those notices that do not pertain to any part of
+          the Derivative Works; and
+
+      (d) If the Work includes a "NOTICE" text file as part of its
+          distribution, then any Derivative Works that You distribute must
+          include a readable copy of the attribution notices contained
+          within such NOTICE file, excluding those notices that do not
+          pertain to any part of the Derivative Works, in at least one
+          of the following places: within a NOTICE text file distributed
+          as part of the Derivative Works; within the Source form or
+          documentation, if provided along with the Derivative Works; or,
+          within a display generated by the Derivative Works, if and
+          wherever such third-party notices normally appear. The contents
+          of the NOTICE file are for informational purposes only and
+          do not modify the License. You may add Your own attribution
+          notices within Derivative Works that You distribute, alongside
+          or as an addendum to the NOTICE text from the Work, provided
+          that such additional attribution notices cannot be construed
+          as modifying the License.
+
+      You may add Your own copyright statement to Your modifications and
+      may provide additional or different license terms and conditions
+      for use, reproduction, or distribution of Your modifications, or
+      for any such Derivative Works as a whole, provided Your use,
+      reproduction, and distribution of the Work otherwise complies with
+      the conditions stated in this License.
+
+   5. Submission of Contributions. Unless You explicitly state otherwise,
+      any Contribution intentionally submitted for inclusion in the Work
+      by You to the Licensor shall be under the terms and conditions of
+      this License, without any additional terms or conditions.
+      Notwithstanding the above, nothing herein shall supersede or modify
+      the terms of any separate license agreement you may have executed
+      with Licensor regarding such Contributions.
+
+   6. Trademarks. This License does not grant permission to use the trade
+      names, trademarks, service marks, or product names of the Licensor,
+      except as required for reasonable and customary use in describing the
+      origin of the Work and reproducing the content of the NOTICE file.
+
+   7. Disclaimer of Warranty. Unless required by applicable law or
+      agreed to in writing, Licensor provides the Work (and each
+      Contributor provides its Contributions) on an "AS IS" BASIS,
+      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+      implied, including, without limitation, any warranties or conditions
+      of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A
+      PARTICULAR PURPOSE. You are solely responsible for determining the
+      appropriateness of using or redistributing the Work and assume any
+      risks associated with Your exercise of permissions under this License.
+
+   8. Limitation of Liability. In no event and under no legal theory,
+      whether in tort (including negligence), contract, or otherwise,
+      unless required by applicable law (such as deliberate and grossly
+      negligent acts) or agreed to in writing, shall any Contributor be
+      liable to You for damages, including any direct, indirect, special,
+      incidental, or consequential damages of any character arising as a
+      result of this License or out of the use or inability to use the
+      Work (including but not limited to damages for loss of goodwill,
+      work stoppage, computer failure or malfunction, or any and all
+      other commercial damages or losses), even if such Contributor
+      has been advised of the possibility of such damages.
+
+   9. Accepting Warranty or Additional Liability. While redistributing
+      the Work or Derivative Works thereof, You may choose to offer,
+      and charge a fee for, acceptance of support, warranty, indemnity,
+      or other liability obligations and/or rights consistent with this
+      License. However, in accepting such obligations, You may act only
+      on Your own behalf and on Your sole responsibility, not on behalf
+      of any other Contributor, and only if You agree to indemnify,
+      defend, and hold each Contributor harmless for any liability
+      incurred by, or claims asserted against, such Contributor by reason
+      of your accepting any such warranty or additional liability.
+
+   END OF TERMS AND CONDITIONS
+
+   APPENDIX: How to apply the Apache License to your work.
+
+      To apply the Apache License to your work, attach the following
+      boilerplate notice, with the fields enclosed by brackets "[]"
+      replaced with your own identifying information. (Don't include
+      the brackets!)  The text should be enclosed in the appropriate
+      comment syntax for the file format. We also recommend that a
+      file or class name and description of purpose be included on the
+      same "printed page" as the copyright notice for easier
+      identification within third-party archives.
+
+   Copyright [yyyy] [name of copyright owner]
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
diff --git a/vendor/cloud.google.com/go/compute/metadata/README.md b/vendor/cloud.google.com/go/compute/metadata/README.md
new file mode 100644
index 0000000..f940fb2
--- /dev/null
+++ b/vendor/cloud.google.com/go/compute/metadata/README.md
@@ -0,0 +1,27 @@
+# Compute API
+
+[![Go Reference](https://pkg.go.dev/badge/cloud.google.com/go/compute.svg)](https://pkg.go.dev/cloud.google.com/go/compute/metadata)
+
+This is a utility library for communicating with Google Cloud metadata service
+on Google Cloud.
+
+## Install
+
+```bash
+go get cloud.google.com/go/compute/metadata
+```
+
+## Go Version Support
+
+See the [Go Versions Supported](https://github.com/googleapis/google-cloud-go#go-versions-supported)
+section in the root directory's README.
+
+## Contributing
+
+Contributions are welcome. Please, see the [CONTRIBUTING](https://github.com/GoogleCloudPlatform/google-cloud-go/blob/main/CONTRIBUTING.md)
+document for details.
+
+Please note that this project is released with a Contributor Code of Conduct.
+By participating in this project you agree to abide by its terms. See
+[Contributor Code of Conduct](https://github.com/GoogleCloudPlatform/google-cloud-go/blob/main/CONTRIBUTING.md#contributor-code-of-conduct)
+for more information.
diff --git a/vendor/cloud.google.com/go/compute/metadata/log.go b/vendor/cloud.google.com/go/compute/metadata/log.go
new file mode 100644
index 0000000..8ec673b
--- /dev/null
+++ b/vendor/cloud.google.com/go/compute/metadata/log.go
@@ -0,0 +1,149 @@
+// Copyright 2024 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package metadata
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"log/slog"
+	"net/http"
+	"strings"
+)
+
+// Code below this point is copied from github.com/googleapis/gax-go/v2/internallog
+// to avoid the dependency. The compute/metadata module is used by too many
+// non-client library modules that can't justify the dependency.
+
+// The handler returned if logging is not enabled.
+type noOpHandler struct{}
+
+func (h noOpHandler) Enabled(_ context.Context, _ slog.Level) bool {
+	return false
+}
+
+func (h noOpHandler) Handle(_ context.Context, _ slog.Record) error {
+	return nil
+}
+
+func (h noOpHandler) WithAttrs(_ []slog.Attr) slog.Handler {
+	return h
+}
+
+func (h noOpHandler) WithGroup(_ string) slog.Handler {
+	return h
+}
+
+// httpRequest returns a lazily evaluated [slog.LogValuer] for a
+// [http.Request] and the associated body.
+func httpRequest(req *http.Request, body []byte) slog.LogValuer {
+	return &request{
+		req:     req,
+		payload: body,
+	}
+}
+
+type request struct {
+	req     *http.Request
+	payload []byte
+}
+
+func (r *request) LogValue() slog.Value {
+	if r == nil || r.req == nil {
+		return slog.Value{}
+	}
+	var groupValueAttrs []slog.Attr
+	groupValueAttrs = append(groupValueAttrs, slog.String("method", r.req.Method))
+	groupValueAttrs = append(groupValueAttrs, slog.String("url", r.req.URL.String()))
+
+	var headerAttr []slog.Attr
+	for k, val := range r.req.Header {
+		headerAttr = append(headerAttr, slog.String(k, strings.Join(val, ",")))
+	}
+	if len(headerAttr) > 0 {
+		groupValueAttrs = append(groupValueAttrs, slog.Any("headers", headerAttr))
+	}
+
+	if len(r.payload) > 0 {
+		if attr, ok := processPayload(r.payload); ok {
+			groupValueAttrs = append(groupValueAttrs, attr)
+		}
+	}
+	return slog.GroupValue(groupValueAttrs...)
+}
+
+// httpResponse returns a lazily evaluated [slog.LogValuer] for a
+// [http.Response] and the associated body.
+func httpResponse(resp *http.Response, body []byte) slog.LogValuer {
+	return &response{
+		resp:    resp,
+		payload: body,
+	}
+}
+
+type response struct {
+	resp    *http.Response
+	payload []byte
+}
+
+func (r *response) LogValue() slog.Value {
+	if r == nil {
+		return slog.Value{}
+	}
+	var groupValueAttrs []slog.Attr
+	groupValueAttrs = append(groupValueAttrs, slog.String("status", fmt.Sprint(r.resp.StatusCode)))
+
+	var headerAttr []slog.Attr
+	for k, val := range r.resp.Header {
+		headerAttr = append(headerAttr, slog.String(k, strings.Join(val, ",")))
+	}
+	if len(headerAttr) > 0 {
+		groupValueAttrs = append(groupValueAttrs, slog.Any("headers", headerAttr))
+	}
+
+	if len(r.payload) > 0 {
+		if attr, ok := processPayload(r.payload); ok {
+			groupValueAttrs = append(groupValueAttrs, attr)
+		}
+	}
+	return slog.GroupValue(groupValueAttrs...)
+}
+
+func processPayload(payload []byte) (slog.Attr, bool) {
+	peekChar := payload[0]
+	if peekChar == '{' {
+		// JSON object
+		var m map[string]any
+		if err := json.Unmarshal(payload, &m); err == nil {
+			return slog.Any("payload", m), true
+		}
+	} else if peekChar == '[' {
+		// JSON array
+		var m []any
+		if err := json.Unmarshal(payload, &m); err == nil {
+			return slog.Any("payload", m), true
+		}
+	} else {
+		// Everything else
+		buf := &bytes.Buffer{}
+		if err := json.Compact(buf, payload); err != nil {
+			// Write raw payload incase of error
+			buf.Write(payload)
+		}
+		return slog.String("payload", buf.String()), true
+	}
+	return slog.Attr{}, false
+}
diff --git a/vendor/cloud.google.com/go/compute/metadata/metadata.go b/vendor/cloud.google.com/go/compute/metadata/metadata.go
new file mode 100644
index 0000000..4c18a38
--- /dev/null
+++ b/vendor/cloud.google.com/go/compute/metadata/metadata.go
@@ -0,0 +1,872 @@
+// Copyright 2014 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package metadata provides access to Google Compute Engine (GCE)
+// metadata and API service accounts.
+//
+// This package is a wrapper around the GCE metadata service,
+// as documented at https://cloud.google.com/compute/docs/metadata/overview.
+package metadata // import "cloud.google.com/go/compute/metadata"
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"log/slog"
+	"net"
+	"net/http"
+	"net/url"
+	"os"
+	"strings"
+	"sync"
+	"time"
+)
+
+const (
+	// metadataIP is the documented metadata server IP address.
+	metadataIP = "169.254.169.254"
+
+	// metadataHostEnv is the environment variable specifying the
+	// GCE metadata hostname.  If empty, the default value of
+	// metadataIP ("169.254.169.254") is used instead.
+	// This is variable name is not defined by any spec, as far as
+	// I know; it was made up for the Go package.
+	metadataHostEnv = "GCE_METADATA_HOST"
+
+	userAgent = "gcloud-golang/0.1"
+)
+
+type cachedValue struct {
+	k    string
+	trim bool
+	mu   sync.Mutex
+	v    string
+}
+
+var (
+	projID  = &cachedValue{k: "project/project-id", trim: true}
+	projNum = &cachedValue{k: "project/numeric-project-id", trim: true}
+	instID  = &cachedValue{k: "instance/id", trim: true}
+)
+
+var defaultClient = &Client{
+	hc:     newDefaultHTTPClient(),
+	logger: slog.New(noOpHandler{}),
+}
+
+func newDefaultHTTPClient() *http.Client {
+	return &http.Client{
+		Transport: &http.Transport{
+			Dial: (&net.Dialer{
+				Timeout:   2 * time.Second,
+				KeepAlive: 30 * time.Second,
+			}).Dial,
+			IdleConnTimeout: 60 * time.Second,
+		},
+		Timeout: 5 * time.Second,
+	}
+}
+
+// NotDefinedError is returned when requested metadata is not defined.
+//
+// The underlying string is the suffix after "/computeMetadata/v1/".
+//
+// This error is not returned if the value is defined to be the empty
+// string.
+type NotDefinedError string
+
+func (suffix NotDefinedError) Error() string {
+	return fmt.Sprintf("metadata: GCE metadata %q not defined", string(suffix))
+}
+
+func (c *cachedValue) get(ctx context.Context, cl *Client) (v string, err error) {
+	defer c.mu.Unlock()
+	c.mu.Lock()
+	if c.v != "" {
+		return c.v, nil
+	}
+	if c.trim {
+		v, err = cl.getTrimmed(ctx, c.k)
+	} else {
+		v, err = cl.GetWithContext(ctx, c.k)
+	}
+	if err == nil {
+		c.v = v
+	}
+	return
+}
+
+var (
+	onGCEOnce sync.Once
+	onGCE     bool
+)
+
+// OnGCE reports whether this process is running on Google Compute Platforms.
+// NOTE: True returned from `OnGCE` does not guarantee that the metadata server
+// is accessible from this process and have all the metadata defined.
+func OnGCE() bool {
+	onGCEOnce.Do(initOnGCE)
+	return onGCE
+}
+
+func initOnGCE() {
+	onGCE = testOnGCE()
+}
+
+func testOnGCE() bool {
+	// The user explicitly said they're on GCE, so trust them.
+	if os.Getenv(metadataHostEnv) != "" {
+		return true
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	resc := make(chan bool, 2)
+
+	// Try two strategies in parallel.
+	// See https://github.com/googleapis/google-cloud-go/issues/194
+	go func() {
+		req, _ := http.NewRequest("GET", "http://"+metadataIP, nil)
+		req.Header.Set("User-Agent", userAgent)
+		res, err := newDefaultHTTPClient().Do(req.WithContext(ctx))
+		if err != nil {
+			resc <- false
+			return
+		}
+		defer res.Body.Close()
+		resc <- res.Header.Get("Metadata-Flavor") == "Google"
+	}()
+
+	go func() {
+		resolver := &net.Resolver{}
+		addrs, err := resolver.LookupHost(ctx, "metadata.google.internal.")
+		if err != nil || len(addrs) == 0 {
+			resc <- false
+			return
+		}
+		resc <- strsContains(addrs, metadataIP)
+	}()
+
+	tryHarder := systemInfoSuggestsGCE()
+	if tryHarder {
+		res := <-resc
+		if res {
+			// The first strategy succeeded, so let's use it.
+			return true
+		}
+		// Wait for either the DNS or metadata server probe to
+		// contradict the other one and say we are running on
+		// GCE. Give it a lot of time to do so, since the system
+		// info already suggests we're running on a GCE BIOS.
+		timer := time.NewTimer(5 * time.Second)
+		defer timer.Stop()
+		select {
+		case res = <-resc:
+			return res
+		case <-timer.C:
+			// Too slow. Who knows what this system is.
+			return false
+		}
+	}
+
+	// There's no hint from the system info that we're running on
+	// GCE, so use the first probe's result as truth, whether it's
+	// true or false. The goal here is to optimize for speed for
+	// users who are NOT running on GCE. We can't assume that
+	// either a DNS lookup or an HTTP request to a blackholed IP
+	// address is fast. Worst case this should return when the
+	// metaClient's Transport.ResponseHeaderTimeout or
+	// Transport.Dial.Timeout fires (in two seconds).
+	return <-resc
+}
+
+// Subscribe calls Client.SubscribeWithContext on the default client.
+//
+// Deprecated: Please use the context aware variant [SubscribeWithContext].
+func Subscribe(suffix string, fn func(v string, ok bool) error) error {
+	return defaultClient.SubscribeWithContext(context.Background(), suffix, func(ctx context.Context, v string, ok bool) error { return fn(v, ok) })
+}
+
+// SubscribeWithContext calls Client.SubscribeWithContext on the default client.
+func SubscribeWithContext(ctx context.Context, suffix string, fn func(ctx context.Context, v string, ok bool) error) error {
+	return defaultClient.SubscribeWithContext(ctx, suffix, fn)
+}
+
+// Get calls Client.GetWithContext on the default client.
+//
+// Deprecated: Please use the context aware variant [GetWithContext].
+func Get(suffix string) (string, error) {
+	return defaultClient.GetWithContext(context.Background(), suffix)
+}
+
+// GetWithContext calls Client.GetWithContext on the default client.
+func GetWithContext(ctx context.Context, suffix string) (string, error) {
+	return defaultClient.GetWithContext(ctx, suffix)
+}
+
+// ProjectID returns the current instance's project ID string.
+//
+// Deprecated: Please use the context aware variant [ProjectIDWithContext].
+func ProjectID() (string, error) {
+	return defaultClient.ProjectIDWithContext(context.Background())
+}
+
+// ProjectIDWithContext returns the current instance's project ID string.
+func ProjectIDWithContext(ctx context.Context) (string, error) {
+	return defaultClient.ProjectIDWithContext(ctx)
+}
+
+// NumericProjectID returns the current instance's numeric project ID.
+//
+// Deprecated: Please use the context aware variant [NumericProjectIDWithContext].
+func NumericProjectID() (string, error) {
+	return defaultClient.NumericProjectIDWithContext(context.Background())
+}
+
+// NumericProjectIDWithContext returns the current instance's numeric project ID.
+func NumericProjectIDWithContext(ctx context.Context) (string, error) {
+	return defaultClient.NumericProjectIDWithContext(ctx)
+}
+
+// InternalIP returns the instance's primary internal IP address.
+//
+// Deprecated: Please use the context aware variant [InternalIPWithContext].
+func InternalIP() (string, error) {
+	return defaultClient.InternalIPWithContext(context.Background())
+}
+
+// InternalIPWithContext returns the instance's primary internal IP address.
+func InternalIPWithContext(ctx context.Context) (string, error) {
+	return defaultClient.InternalIPWithContext(ctx)
+}
+
+// ExternalIP returns the instance's primary external (public) IP address.
+//
+// Deprecated: Please use the context aware variant [ExternalIPWithContext].
+func ExternalIP() (string, error) {
+	return defaultClient.ExternalIPWithContext(context.Background())
+}
+
+// ExternalIPWithContext returns the instance's primary external (public) IP address.
+func ExternalIPWithContext(ctx context.Context) (string, error) {
+	return defaultClient.ExternalIPWithContext(ctx)
+}
+
+// Email calls Client.EmailWithContext on the default client.
+//
+// Deprecated: Please use the context aware variant [EmailWithContext].
+func Email(serviceAccount string) (string, error) {
+	return defaultClient.EmailWithContext(context.Background(), serviceAccount)
+}
+
+// EmailWithContext calls Client.EmailWithContext on the default client.
+func EmailWithContext(ctx context.Context, serviceAccount string) (string, error) {
+	return defaultClient.EmailWithContext(ctx, serviceAccount)
+}
+
+// Hostname returns the instance's hostname. This will be of the form
+// "<instanceID>.c.<projID>.internal".
+//
+// Deprecated: Please use the context aware variant [HostnameWithContext].
+func Hostname() (string, error) {
+	return defaultClient.HostnameWithContext(context.Background())
+}
+
+// HostnameWithContext returns the instance's hostname. This will be of the form
+// "<instanceID>.c.<projID>.internal".
+func HostnameWithContext(ctx context.Context) (string, error) {
+	return defaultClient.HostnameWithContext(ctx)
+}
+
+// InstanceTags returns the list of user-defined instance tags,
+// assigned when initially creating a GCE instance.
+//
+// Deprecated: Please use the context aware variant [InstanceTagsWithContext].
+func InstanceTags() ([]string, error) {
+	return defaultClient.InstanceTagsWithContext(context.Background())
+}
+
+// InstanceTagsWithContext returns the list of user-defined instance tags,
+// assigned when initially creating a GCE instance.
+func InstanceTagsWithContext(ctx context.Context) ([]string, error) {
+	return defaultClient.InstanceTagsWithContext(ctx)
+}
+
+// InstanceID returns the current VM's numeric instance ID.
+//
+// Deprecated: Please use the context aware variant [InstanceIDWithContext].
+func InstanceID() (string, error) {
+	return defaultClient.InstanceIDWithContext(context.Background())
+}
+
+// InstanceIDWithContext returns the current VM's numeric instance ID.
+func InstanceIDWithContext(ctx context.Context) (string, error) {
+	return defaultClient.InstanceIDWithContext(ctx)
+}
+
+// InstanceName returns the current VM's instance ID string.
+//
+// Deprecated: Please use the context aware variant [InstanceNameWithContext].
+func InstanceName() (string, error) {
+	return defaultClient.InstanceNameWithContext(context.Background())
+}
+
+// InstanceNameWithContext returns the current VM's instance ID string.
+func InstanceNameWithContext(ctx context.Context) (string, error) {
+	return defaultClient.InstanceNameWithContext(ctx)
+}
+
+// Zone returns the current VM's zone, such as "us-central1-b".
+//
+// Deprecated: Please use the context aware variant [ZoneWithContext].
+func Zone() (string, error) {
+	return defaultClient.ZoneWithContext(context.Background())
+}
+
+// ZoneWithContext returns the current VM's zone, such as "us-central1-b".
+func ZoneWithContext(ctx context.Context) (string, error) {
+	return defaultClient.ZoneWithContext(ctx)
+}
+
+// InstanceAttributes calls Client.InstanceAttributesWithContext on the default client.
+//
+// Deprecated: Please use the context aware variant [InstanceAttributesWithContext.
+func InstanceAttributes() ([]string, error) {
+	return defaultClient.InstanceAttributesWithContext(context.Background())
+}
+
+// InstanceAttributesWithContext calls Client.ProjectAttributesWithContext on the default client.
+func InstanceAttributesWithContext(ctx context.Context) ([]string, error) {
+	return defaultClient.InstanceAttributesWithContext(ctx)
+}
+
+// ProjectAttributes calls Client.ProjectAttributesWithContext on the default client.
+//
+// Deprecated: Please use the context aware variant [ProjectAttributesWithContext].
+func ProjectAttributes() ([]string, error) {
+	return defaultClient.ProjectAttributesWithContext(context.Background())
+}
+
+// ProjectAttributesWithContext calls Client.ProjectAttributesWithContext on the default client.
+func ProjectAttributesWithContext(ctx context.Context) ([]string, error) {
+	return defaultClient.ProjectAttributesWithContext(ctx)
+}
+
+// InstanceAttributeValue calls Client.InstanceAttributeValueWithContext on the default client.
+//
+// Deprecated: Please use the context aware variant [InstanceAttributeValueWithContext].
+func InstanceAttributeValue(attr string) (string, error) {
+	return defaultClient.InstanceAttributeValueWithContext(context.Background(), attr)
+}
+
+// InstanceAttributeValueWithContext calls Client.InstanceAttributeValueWithContext on the default client.
+func InstanceAttributeValueWithContext(ctx context.Context, attr string) (string, error) {
+	return defaultClient.InstanceAttributeValueWithContext(ctx, attr)
+}
+
+// ProjectAttributeValue calls Client.ProjectAttributeValueWithContext on the default client.
+//
+// Deprecated: Please use the context aware variant [ProjectAttributeValueWithContext].
+func ProjectAttributeValue(attr string) (string, error) {
+	return defaultClient.ProjectAttributeValueWithContext(context.Background(), attr)
+}
+
+// ProjectAttributeValueWithContext calls Client.ProjectAttributeValueWithContext on the default client.
+func ProjectAttributeValueWithContext(ctx context.Context, attr string) (string, error) {
+	return defaultClient.ProjectAttributeValueWithContext(ctx, attr)
+}
+
+// Scopes calls Client.ScopesWithContext on the default client.
+//
+// Deprecated: Please use the context aware variant [ScopesWithContext].
+func Scopes(serviceAccount string) ([]string, error) {
+	return defaultClient.ScopesWithContext(context.Background(), serviceAccount)
+}
+
+// ScopesWithContext calls Client.ScopesWithContext on the default client.
+func ScopesWithContext(ctx context.Context, serviceAccount string) ([]string, error) {
+	return defaultClient.ScopesWithContext(ctx, serviceAccount)
+}
+
+func strsContains(ss []string, s string) bool {
+	for _, v := range ss {
+		if v == s {
+			return true
+		}
+	}
+	return false
+}
+
+// A Client provides metadata.
+type Client struct {
+	hc     *http.Client
+	logger *slog.Logger
+}
+
+// Options for configuring a [Client].
+type Options struct {
+	// Client is the HTTP client used to make requests. Optional.
+	Client *http.Client
+	// Logger is used to log information about HTTP request and responses.
+	// If not provided, nothing will be logged. Optional.
+	Logger *slog.Logger
+}
+
+// NewClient returns a Client that can be used to fetch metadata.
+// Returns the client that uses the specified http.Client for HTTP requests.
+// If nil is specified, returns the default client.
+func NewClient(c *http.Client) *Client {
+	return NewWithOptions(&Options{
+		Client: c,
+	})
+}
+
+// NewWithOptions returns a Client that is configured with the provided Options.
+func NewWithOptions(opts *Options) *Client {
+	if opts == nil {
+		return defaultClient
+	}
+	client := opts.Client
+	if client == nil {
+		client = newDefaultHTTPClient()
+	}
+	logger := opts.Logger
+	if logger == nil {
+		logger = slog.New(noOpHandler{})
+	}
+	return &Client{hc: client, logger: logger}
+}
+
+// getETag returns a value from the metadata service as well as the associated ETag.
+// This func is otherwise equivalent to Get.
+func (c *Client) getETag(ctx context.Context, suffix string) (value, etag string, err error) {
+	// Using a fixed IP makes it very difficult to spoof the metadata service in
+	// a container, which is an important use-case for local testing of cloud
+	// deployments. To enable spoofing of the metadata service, the environment
+	// variable GCE_METADATA_HOST is first inspected to decide where metadata
+	// requests shall go.
+	host := os.Getenv(metadataHostEnv)
+	if host == "" {
+		// Using 169.254.169.254 instead of "metadata" here because Go
+		// binaries built with the "netgo" tag and without cgo won't
+		// know the search suffix for "metadata" is
+		// ".google.internal", and this IP address is documented as
+		// being stable anyway.
+		host = metadataIP
+	}
+	suffix = strings.TrimLeft(suffix, "/")
+	u := "http://" + host + "/computeMetadata/v1/" + suffix
+	req, err := http.NewRequestWithContext(ctx, "GET", u, nil)
+	if err != nil {
+		return "", "", err
+	}
+	req.Header.Set("Metadata-Flavor", "Google")
+	req.Header.Set("User-Agent", userAgent)
+	var res *http.Response
+	var reqErr error
+	var body []byte
+	retryer := newRetryer()
+	for {
+		c.logger.DebugContext(ctx, "metadata request", "request", httpRequest(req, nil))
+		res, reqErr = c.hc.Do(req)
+		var code int
+		if res != nil {
+			code = res.StatusCode
+			body, err = io.ReadAll(res.Body)
+			if err != nil {
+				res.Body.Close()
+				return "", "", err
+			}
+			c.logger.DebugContext(ctx, "metadata response", "response", httpResponse(res, body))
+			res.Body.Close()
+		}
+		if delay, shouldRetry := retryer.Retry(code, reqErr); shouldRetry {
+			if res != nil && res.Body != nil {
+				res.Body.Close()
+			}
+			if err := sleep(ctx, delay); err != nil {
+				return "", "", err
+			}
+			continue
+		}
+		break
+	}
+	if reqErr != nil {
+		return "", "", reqErr
+	}
+	if res.StatusCode == http.StatusNotFound {
+		return "", "", NotDefinedError(suffix)
+	}
+	if res.StatusCode != 200 {
+		return "", "", &Error{Code: res.StatusCode, Message: string(body)}
+	}
+	return string(body), res.Header.Get("Etag"), nil
+}
+
+// Get returns a value from the metadata service.
+// The suffix is appended to "http://${GCE_METADATA_HOST}/computeMetadata/v1/".
+//
+// If the GCE_METADATA_HOST environment variable is not defined, a default of
+// 169.254.169.254 will be used instead.
+//
+// If the requested metadata is not defined, the returned error will
+// be of type NotDefinedError.
+//
+// Deprecated: Please use the context aware variant [Client.GetWithContext].
+func (c *Client) Get(suffix string) (string, error) {
+	return c.GetWithContext(context.Background(), suffix)
+}
+
+// GetWithContext returns a value from the metadata service.
+// The suffix is appended to "http://${GCE_METADATA_HOST}/computeMetadata/v1/".
+//
+// If the GCE_METADATA_HOST environment variable is not defined, a default of
+// 169.254.169.254 will be used instead.
+//
+// If the requested metadata is not defined, the returned error will
+// be of type NotDefinedError.
+//
+// NOTE: Without an extra deadline in the context this call can take in the
+// worst case, with internal backoff retries, up to 15 seconds (e.g. when server
+// is responding slowly). Pass context with additional timeouts when needed.
+func (c *Client) GetWithContext(ctx context.Context, suffix string) (string, error) {
+	val, _, err := c.getETag(ctx, suffix)
+	return val, err
+}
+
+func (c *Client) getTrimmed(ctx context.Context, suffix string) (s string, err error) {
+	s, err = c.GetWithContext(ctx, suffix)
+	s = strings.TrimSpace(s)
+	return
+}
+
+func (c *Client) lines(ctx context.Context, suffix string) ([]string, error) {
+	j, err := c.GetWithContext(ctx, suffix)
+	if err != nil {
+		return nil, err
+	}
+	s := strings.Split(strings.TrimSpace(j), "\n")
+	for i := range s {
+		s[i] = strings.TrimSpace(s[i])
+	}
+	return s, nil
+}
+
+// ProjectID returns the current instance's project ID string.
+//
+// Deprecated: Please use the context aware variant [Client.ProjectIDWithContext].
+func (c *Client) ProjectID() (string, error) { return c.ProjectIDWithContext(context.Background()) }
+
+// ProjectIDWithContext returns the current instance's project ID string.
+func (c *Client) ProjectIDWithContext(ctx context.Context) (string, error) { return projID.get(ctx, c) }
+
+// NumericProjectID returns the current instance's numeric project ID.
+//
+// Deprecated: Please use the context aware variant [Client.NumericProjectIDWithContext].
+func (c *Client) NumericProjectID() (string, error) {
+	return c.NumericProjectIDWithContext(context.Background())
+}
+
+// NumericProjectIDWithContext returns the current instance's numeric project ID.
+func (c *Client) NumericProjectIDWithContext(ctx context.Context) (string, error) {
+	return projNum.get(ctx, c)
+}
+
+// InstanceID returns the current VM's numeric instance ID.
+//
+// Deprecated: Please use the context aware variant [Client.InstanceIDWithContext].
+func (c *Client) InstanceID() (string, error) {
+	return c.InstanceIDWithContext(context.Background())
+}
+
+// InstanceIDWithContext returns the current VM's numeric instance ID.
+func (c *Client) InstanceIDWithContext(ctx context.Context) (string, error) {
+	return instID.get(ctx, c)
+}
+
+// InternalIP returns the instance's primary internal IP address.
+//
+// Deprecated: Please use the context aware variant [Client.InternalIPWithContext].
+func (c *Client) InternalIP() (string, error) {
+	return c.InternalIPWithContext(context.Background())
+}
+
+// InternalIPWithContext returns the instance's primary internal IP address.
+func (c *Client) InternalIPWithContext(ctx context.Context) (string, error) {
+	return c.getTrimmed(ctx, "instance/network-interfaces/0/ip")
+}
+
+// Email returns the email address associated with the service account.
+//
+// Deprecated: Please use the context aware variant [Client.EmailWithContext].
+func (c *Client) Email(serviceAccount string) (string, error) {
+	return c.EmailWithContext(context.Background(), serviceAccount)
+}
+
+// EmailWithContext returns the email address associated with the service account.
+// The serviceAccount parameter default value (empty string or "default" value)
+// will use the instance's main account.
+func (c *Client) EmailWithContext(ctx context.Context, serviceAccount string) (string, error) {
+	if serviceAccount == "" {
+		serviceAccount = "default"
+	}
+	return c.getTrimmed(ctx, "instance/service-accounts/"+serviceAccount+"/email")
+}
+
+// ExternalIP returns the instance's primary external (public) IP address.
+//
+// Deprecated: Please use the context aware variant [Client.ExternalIPWithContext].
+func (c *Client) ExternalIP() (string, error) {
+	return c.ExternalIPWithContext(context.Background())
+}
+
+// ExternalIPWithContext returns the instance's primary external (public) IP address.
+func (c *Client) ExternalIPWithContext(ctx context.Context) (string, error) {
+	return c.getTrimmed(ctx, "instance/network-interfaces/0/access-configs/0/external-ip")
+}
+
+// Hostname returns the instance's hostname. This will be of the form
+// "<instanceID>.c.<projID>.internal".
+//
+// Deprecated: Please use the context aware variant [Client.HostnameWithContext].
+func (c *Client) Hostname() (string, error) {
+	return c.HostnameWithContext(context.Background())
+}
+
+// HostnameWithContext returns the instance's hostname. This will be of the form
+// "<instanceID>.c.<projID>.internal".
+func (c *Client) HostnameWithContext(ctx context.Context) (string, error) {
+	return c.getTrimmed(ctx, "instance/hostname")
+}
+
+// InstanceTags returns the list of user-defined instance tags.
+//
+// Deprecated: Please use the context aware variant [Client.InstanceTagsWithContext].
+func (c *Client) InstanceTags() ([]string, error) {
+	return c.InstanceTagsWithContext(context.Background())
+}
+
+// InstanceTagsWithContext returns the list of user-defined instance tags,
+// assigned when initially creating a GCE instance.
+func (c *Client) InstanceTagsWithContext(ctx context.Context) ([]string, error) {
+	var s []string
+	j, err := c.GetWithContext(ctx, "instance/tags")
+	if err != nil {
+		return nil, err
+	}
+	if err := json.NewDecoder(strings.NewReader(j)).Decode(&s); err != nil {
+		return nil, err
+	}
+	return s, nil
+}
+
+// InstanceName returns the current VM's instance ID string.
+//
+// Deprecated: Please use the context aware variant [Client.InstanceNameWithContext].
+func (c *Client) InstanceName() (string, error) {
+	return c.InstanceNameWithContext(context.Background())
+}
+
+// InstanceNameWithContext returns the current VM's instance ID string.
+func (c *Client) InstanceNameWithContext(ctx context.Context) (string, error) {
+	return c.getTrimmed(ctx, "instance/name")
+}
+
+// Zone returns the current VM's zone, such as "us-central1-b".
+//
+// Deprecated: Please use the context aware variant [Client.ZoneWithContext].
+func (c *Client) Zone() (string, error) {
+	return c.ZoneWithContext(context.Background())
+}
+
+// ZoneWithContext returns the current VM's zone, such as "us-central1-b".
+func (c *Client) ZoneWithContext(ctx context.Context) (string, error) {
+	zone, err := c.getTrimmed(ctx, "instance/zone")
+	// zone is of the form "projects/<projNum>/zones/<zoneName>".
+	if err != nil {
+		return "", err
+	}
+	return zone[strings.LastIndex(zone, "/")+1:], nil
+}
+
+// InstanceAttributes returns the list of user-defined attributes,
+// assigned when initially creating a GCE VM instance. The value of an
+// attribute can be obtained with InstanceAttributeValue.
+//
+// Deprecated: Please use the context aware variant [Client.InstanceAttributesWithContext].
+func (c *Client) InstanceAttributes() ([]string, error) {
+	return c.InstanceAttributesWithContext(context.Background())
+}
+
+// InstanceAttributesWithContext returns the list of user-defined attributes,
+// assigned when initially creating a GCE VM instance. The value of an
+// attribute can be obtained with InstanceAttributeValue.
+func (c *Client) InstanceAttributesWithContext(ctx context.Context) ([]string, error) {
+	return c.lines(ctx, "instance/attributes/")
+}
+
+// ProjectAttributes returns the list of user-defined attributes
+// applying to the project as a whole, not just this VM.  The value of
+// an attribute can be obtained with ProjectAttributeValue.
+//
+// Deprecated: Please use the context aware variant [Client.ProjectAttributesWithContext].
+func (c *Client) ProjectAttributes() ([]string, error) {
+	return c.ProjectAttributesWithContext(context.Background())
+}
+
+// ProjectAttributesWithContext returns the list of user-defined attributes
+// applying to the project as a whole, not just this VM.  The value of
+// an attribute can be obtained with ProjectAttributeValue.
+func (c *Client) ProjectAttributesWithContext(ctx context.Context) ([]string, error) {
+	return c.lines(ctx, "project/attributes/")
+}
+
+// InstanceAttributeValue returns the value of the provided VM
+// instance attribute.
+//
+// If the requested attribute is not defined, the returned error will
+// be of type NotDefinedError.
+//
+// InstanceAttributeValue may return ("", nil) if the attribute was
+// defined to be the empty string.
+//
+// Deprecated: Please use the context aware variant [Client.InstanceAttributeValueWithContext].
+func (c *Client) InstanceAttributeValue(attr string) (string, error) {
+	return c.InstanceAttributeValueWithContext(context.Background(), attr)
+}
+
+// InstanceAttributeValueWithContext returns the value of the provided VM
+// instance attribute.
+//
+// If the requested attribute is not defined, the returned error will
+// be of type NotDefinedError.
+//
+// InstanceAttributeValue may return ("", nil) if the attribute was
+// defined to be the empty string.
+func (c *Client) InstanceAttributeValueWithContext(ctx context.Context, attr string) (string, error) {
+	return c.GetWithContext(ctx, "instance/attributes/"+attr)
+}
+
+// ProjectAttributeValue returns the value of the provided
+// project attribute.
+//
+// If the requested attribute is not defined, the returned error will
+// be of type NotDefinedError.
+//
+// ProjectAttributeValue may return ("", nil) if the attribute was
+// defined to be the empty string.
+//
+// Deprecated: Please use the context aware variant [Client.ProjectAttributeValueWithContext].
+func (c *Client) ProjectAttributeValue(attr string) (string, error) {
+	return c.ProjectAttributeValueWithContext(context.Background(), attr)
+}
+
+// ProjectAttributeValueWithContext returns the value of the provided
+// project attribute.
+//
+// If the requested attribute is not defined, the returned error will
+// be of type NotDefinedError.
+//
+// ProjectAttributeValue may return ("", nil) if the attribute was
+// defined to be the empty string.
+func (c *Client) ProjectAttributeValueWithContext(ctx context.Context, attr string) (string, error) {
+	return c.GetWithContext(ctx, "project/attributes/"+attr)
+}
+
+// Scopes returns the service account scopes for the given account.
+// The account may be empty or the string "default" to use the instance's
+// main account.
+//
+// Deprecated: Please use the context aware variant [Client.ScopesWithContext].
+func (c *Client) Scopes(serviceAccount string) ([]string, error) {
+	return c.ScopesWithContext(context.Background(), serviceAccount)
+}
+
+// ScopesWithContext returns the service account scopes for the given account.
+// The account may be empty or the string "default" to use the instance's
+// main account.
+func (c *Client) ScopesWithContext(ctx context.Context, serviceAccount string) ([]string, error) {
+	if serviceAccount == "" {
+		serviceAccount = "default"
+	}
+	return c.lines(ctx, "instance/service-accounts/"+serviceAccount+"/scopes")
+}
+
+// Subscribe subscribes to a value from the metadata service.
+// The suffix is appended to "http://${GCE_METADATA_HOST}/computeMetadata/v1/".
+// The suffix may contain query parameters.
+//
+// Deprecated: Please use the context aware variant [Client.SubscribeWithContext].
+func (c *Client) Subscribe(suffix string, fn func(v string, ok bool) error) error {
+	return c.SubscribeWithContext(context.Background(), suffix, func(ctx context.Context, v string, ok bool) error { return fn(v, ok) })
+}
+
+// SubscribeWithContext subscribes to a value from the metadata service.
+// The suffix is appended to "http://${GCE_METADATA_HOST}/computeMetadata/v1/".
+// The suffix may contain query parameters.
+//
+// SubscribeWithContext calls fn with the latest metadata value indicated by the
+// provided suffix. If the metadata value is deleted, fn is called with the
+// empty string and ok false. Subscribe blocks until fn returns a non-nil error
+// or the value is deleted. Subscribe returns the error value returned from the
+// last call to fn, which may be nil when ok == false.
+func (c *Client) SubscribeWithContext(ctx context.Context, suffix string, fn func(ctx context.Context, v string, ok bool) error) error {
+	const failedSubscribeSleep = time.Second * 5
+
+	// First check to see if the metadata value exists at all.
+	val, lastETag, err := c.getETag(ctx, suffix)
+	if err != nil {
+		return err
+	}
+
+	if err := fn(ctx, val, true); err != nil {
+		return err
+	}
+
+	ok := true
+	if strings.ContainsRune(suffix, '?') {
+		suffix += "&wait_for_change=true&last_etag="
+	} else {
+		suffix += "?wait_for_change=true&last_etag="
+	}
+	for {
+		val, etag, err := c.getETag(ctx, suffix+url.QueryEscape(lastETag))
+		if err != nil {
+			if _, deleted := err.(NotDefinedError); !deleted {
+				time.Sleep(failedSubscribeSleep)
+				continue // Retry on other errors.
+			}
+			ok = false
+		}
+		lastETag = etag
+
+		if err := fn(ctx, val, ok); err != nil || !ok {
+			return err
+		}
+	}
+}
+
+// Error contains an error response from the server.
+type Error struct {
+	// Code is the HTTP response status code.
+	Code int
+	// Message is the server response message.
+	Message string
+}
+
+func (e *Error) Error() string {
+	return fmt.Sprintf("compute: Received %d `%s`", e.Code, e.Message)
+}
diff --git a/vendor/cloud.google.com/go/compute/metadata/retry.go b/vendor/cloud.google.com/go/compute/metadata/retry.go
new file mode 100644
index 0000000..3d4bc75
--- /dev/null
+++ b/vendor/cloud.google.com/go/compute/metadata/retry.go
@@ -0,0 +1,114 @@
+// Copyright 2021 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package metadata
+
+import (
+	"context"
+	"io"
+	"math/rand"
+	"net/http"
+	"time"
+)
+
+const (
+	maxRetryAttempts = 5
+)
+
+var (
+	syscallRetryable = func(error) bool { return false }
+)
+
+// defaultBackoff is basically equivalent to gax.Backoff without the need for
+// the dependency.
+type defaultBackoff struct {
+	max time.Duration
+	mul float64
+	cur time.Duration
+}
+
+func (b *defaultBackoff) Pause() time.Duration {
+	d := time.Duration(1 + rand.Int63n(int64(b.cur)))
+	b.cur = time.Duration(float64(b.cur) * b.mul)
+	if b.cur > b.max {
+		b.cur = b.max
+	}
+	return d
+}
+
+// sleep is the equivalent of gax.Sleep without the need for the dependency.
+func sleep(ctx context.Context, d time.Duration) error {
+	t := time.NewTimer(d)
+	select {
+	case <-ctx.Done():
+		t.Stop()
+		return ctx.Err()
+	case <-t.C:
+		return nil
+	}
+}
+
+func newRetryer() *metadataRetryer {
+	return &metadataRetryer{bo: &defaultBackoff{
+		cur: 100 * time.Millisecond,
+		max: 30 * time.Second,
+		mul: 2,
+	}}
+}
+
+type backoff interface {
+	Pause() time.Duration
+}
+
+type metadataRetryer struct {
+	bo       backoff
+	attempts int
+}
+
+func (r *metadataRetryer) Retry(status int, err error) (time.Duration, bool) {
+	if status == http.StatusOK {
+		return 0, false
+	}
+	retryOk := shouldRetry(status, err)
+	if !retryOk {
+		return 0, false
+	}
+	if r.attempts == maxRetryAttempts {
+		return 0, false
+	}
+	r.attempts++
+	return r.bo.Pause(), true
+}
+
+func shouldRetry(status int, err error) bool {
+	if 500 <= status && status <= 599 {
+		return true
+	}
+	if err == io.ErrUnexpectedEOF {
+		return true
+	}
+	// Transient network errors should be retried.
+	if syscallRetryable(err) {
+		return true
+	}
+	if err, ok := err.(interface{ Temporary() bool }); ok {
+		if err.Temporary() {
+			return true
+		}
+	}
+	if err, ok := err.(interface{ Unwrap() error }); ok {
+		return shouldRetry(status, err.Unwrap())
+	}
+	return false
+}
diff --git a/vendor/cloud.google.com/go/compute/metadata/retry_linux.go b/vendor/cloud.google.com/go/compute/metadata/retry_linux.go
new file mode 100644
index 0000000..2e53f01
--- /dev/null
+++ b/vendor/cloud.google.com/go/compute/metadata/retry_linux.go
@@ -0,0 +1,31 @@
+// Copyright 2021 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//go:build linux
+// +build linux
+
+package metadata
+
+import (
+	"errors"
+	"syscall"
+)
+
+func init() {
+	// Initialize syscallRetryable to return true on transient socket-level
+	// errors. These errors are specific to Linux.
+	syscallRetryable = func(err error) bool {
+		return errors.Is(err, syscall.ECONNRESET) || errors.Is(err, syscall.ECONNREFUSED)
+	}
+}
diff --git a/vendor/cloud.google.com/go/compute/metadata/syscheck.go b/vendor/cloud.google.com/go/compute/metadata/syscheck.go
new file mode 100644
index 0000000..e0704fa
--- /dev/null
+++ b/vendor/cloud.google.com/go/compute/metadata/syscheck.go
@@ -0,0 +1,26 @@
+// Copyright 2024 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//go:build !windows && !linux
+
+package metadata
+
+// systemInfoSuggestsGCE reports whether the local system (without
+// doing network requests) suggests that we're running on GCE. If this
+// returns true, testOnGCE tries a bit harder to reach its metadata
+// server.
+func systemInfoSuggestsGCE() bool {
+	// We don't currently have checks for other GOOS
+	return false
+}
diff --git a/vendor/cloud.google.com/go/compute/metadata/syscheck_linux.go b/vendor/cloud.google.com/go/compute/metadata/syscheck_linux.go
new file mode 100644
index 0000000..74689ac
--- /dev/null
+++ b/vendor/cloud.google.com/go/compute/metadata/syscheck_linux.go
@@ -0,0 +1,28 @@
+// Copyright 2024 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//go:build linux
+
+package metadata
+
+import (
+	"os"
+	"strings"
+)
+
+func systemInfoSuggestsGCE() bool {
+	b, _ := os.ReadFile("/sys/class/dmi/id/product_name")
+	name := strings.TrimSpace(string(b))
+	return name == "Google" || name == "Google Compute Engine"
+}
diff --git a/vendor/cloud.google.com/go/compute/metadata/syscheck_windows.go b/vendor/cloud.google.com/go/compute/metadata/syscheck_windows.go
new file mode 100644
index 0000000..c0ce627
--- /dev/null
+++ b/vendor/cloud.google.com/go/compute/metadata/syscheck_windows.go
@@ -0,0 +1,38 @@
+// Copyright 2024 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//go:build windows
+
+package metadata
+
+import (
+	"strings"
+
+	"golang.org/x/sys/windows/registry"
+)
+
+func systemInfoSuggestsGCE() bool {
+	k, err := registry.OpenKey(registry.LOCAL_MACHINE, `SYSTEM\HardwareConfig\Current`, registry.QUERY_VALUE)
+	if err != nil {
+		return false
+	}
+	defer k.Close()
+
+	s, _, err := k.GetStringValue("SystemProductName")
+	if err != nil {
+		return false
+	}
+	s = strings.TrimSpace(s)
+	return strings.HasPrefix(s, "Google")
+}