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// Copyright 2023 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 credentials
import (
"context"
"encoding/json"
"errors"
"fmt"
"net/url"
"strings"
"time"
"cloud.google.com/go/auth"
"cloud.google.com/go/compute/metadata"
)
var (
computeTokenMetadata = map[string]interface{}{
"auth.google.tokenSource": "compute-metadata",
"auth.google.serviceAccount": "default",
}
computeTokenURI = "instance/service-accounts/default/token"
)
// computeTokenProvider creates a [cloud.google.com/go/auth.TokenProvider] that
// uses the metadata service to retrieve tokens.
func computeTokenProvider(opts *DetectOptions, client *metadata.Client) auth.TokenProvider {
return auth.NewCachedTokenProvider(&computeProvider{
scopes: opts.Scopes,
client: client,
tokenBindingType: opts.TokenBindingType,
}, &auth.CachedTokenProviderOptions{
ExpireEarly: opts.EarlyTokenRefresh,
DisableAsyncRefresh: opts.DisableAsyncRefresh,
})
}
// computeProvider fetches tokens from the google cloud metadata service.
type computeProvider struct {
scopes []string
client *metadata.Client
tokenBindingType TokenBindingType
}
type metadataTokenResp struct {
AccessToken string `json:"access_token"`
ExpiresInSec int `json:"expires_in"`
TokenType string `json:"token_type"`
}
func (cs *computeProvider) Token(ctx context.Context) (*auth.Token, error) {
tokenURI, err := url.Parse(computeTokenURI)
if err != nil {
return nil, err
}
hasScopes := len(cs.scopes) > 0
if hasScopes || cs.tokenBindingType != NoBinding {
v := url.Values{}
if hasScopes {
v.Set("scopes", strings.Join(cs.scopes, ","))
}
switch cs.tokenBindingType {
case MTLSHardBinding:
v.Set("transport", "mtls")
v.Set("binding-enforcement", "on")
case ALTSHardBinding:
v.Set("transport", "alts")
}
tokenURI.RawQuery = v.Encode()
}
tokenJSON, err := cs.client.GetWithContext(ctx, tokenURI.String())
if err != nil {
return nil, fmt.Errorf("credentials: cannot fetch token: %w", err)
}
var res metadataTokenResp
if err := json.NewDecoder(strings.NewReader(tokenJSON)).Decode(&res); err != nil {
return nil, fmt.Errorf("credentials: invalid token JSON from metadata: %w", err)
}
if res.ExpiresInSec == 0 || res.AccessToken == "" {
return nil, errors.New("credentials: incomplete token received from metadata")
}
return &auth.Token{
Value: res.AccessToken,
Type: res.TokenType,
Expiry: time.Now().Add(time.Duration(res.ExpiresInSec) * time.Second),
Metadata: computeTokenMetadata,
}, nil
}
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