1// Copyright 2023 Google LLC
2//
3// Licensed under the Apache License, Version 2.0 (the "License");
4// you may not use this file except in compliance with the License.
5// You may obtain a copy of the License at
6//
7// http://www.apache.org/licenses/LICENSE-2.0
8//
9// Unless required by applicable law or agreed to in writing, software
10// distributed under the License is distributed on an "AS IS" BASIS,
11// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12// See the License for the specific language governing permissions and
13// limitations under the License.
14
15package credentials
16
17import (
18 "context"
19 "encoding/json"
20 "errors"
21 "fmt"
22 "net/url"
23 "strings"
24 "time"
25
26 "cloud.google.com/go/auth"
27 "cloud.google.com/go/compute/metadata"
28)
29
30var (
31 computeTokenMetadata = map[string]interface{}{
32 "auth.google.tokenSource": "compute-metadata",
33 "auth.google.serviceAccount": "default",
34 }
35 computeTokenURI = "instance/service-accounts/default/token"
36)
37
38// computeTokenProvider creates a [cloud.google.com/go/auth.TokenProvider] that
39// uses the metadata service to retrieve tokens.
40func computeTokenProvider(opts *DetectOptions, client *metadata.Client) auth.TokenProvider {
41 return auth.NewCachedTokenProvider(&computeProvider{
42 scopes: opts.Scopes,
43 client: client,
44 }, &auth.CachedTokenProviderOptions{
45 ExpireEarly: opts.EarlyTokenRefresh,
46 DisableAsyncRefresh: opts.DisableAsyncRefresh,
47 })
48}
49
50// computeProvider fetches tokens from the google cloud metadata service.
51type computeProvider struct {
52 scopes []string
53 client *metadata.Client
54}
55
56type metadataTokenResp struct {
57 AccessToken string `json:"access_token"`
58 ExpiresInSec int `json:"expires_in"`
59 TokenType string `json:"token_type"`
60}
61
62func (cs *computeProvider) Token(ctx context.Context) (*auth.Token, error) {
63 tokenURI, err := url.Parse(computeTokenURI)
64 if err != nil {
65 return nil, err
66 }
67 if len(cs.scopes) > 0 {
68 v := url.Values{}
69 v.Set("scopes", strings.Join(cs.scopes, ","))
70 tokenURI.RawQuery = v.Encode()
71 }
72 tokenJSON, err := cs.client.GetWithContext(ctx, tokenURI.String())
73 if err != nil {
74 return nil, fmt.Errorf("credentials: cannot fetch token: %w", err)
75 }
76 var res metadataTokenResp
77 if err := json.NewDecoder(strings.NewReader(tokenJSON)).Decode(&res); err != nil {
78 return nil, fmt.Errorf("credentials: invalid token JSON from metadata: %w", err)
79 }
80 if res.ExpiresInSec == 0 || res.AccessToken == "" {
81 return nil, errors.New("credentials: incomplete token received from metadata")
82 }
83 return &auth.Token{
84 Value: res.AccessToken,
85 Type: res.TokenType,
86 Expiry: time.Now().Add(time.Duration(res.ExpiresInSec) * time.Second),
87 Metadata: computeTokenMetadata,
88 }, nil
89
90}