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selfsignedjwt.go
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selfsignedjwt.go
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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"
"crypto/rsa"
"fmt"
"strings"
"time"
"cloud.google.com/go/auth"
"cloud.google.com/go/auth/internal"
"cloud.google.com/go/auth/internal/credsfile"
"cloud.google.com/go/auth/internal/jwt"
)
var (
// for testing
now func() time.Time = time.Now
)
// configureSelfSignedJWT uses the private key in the service account to create
// a JWT without making a network call.
func configureSelfSignedJWT(f *credsfile.ServiceAccountFile, opts *DetectOptions) (auth.TokenProvider, error) {
pk, err := internal.ParseKey([]byte(f.PrivateKey))
if err != nil {
return nil, fmt.Errorf("credentials: could not parse key: %w", err)
}
return &selfSignedTokenProvider{
email: f.ClientEmail,
audience: opts.Audience,
scopes: opts.scopes(),
pk: pk,
pkID: f.PrivateKeyID,
}, nil
}
type selfSignedTokenProvider struct {
email string
audience string
scopes []string
pk *rsa.PrivateKey
pkID string
}
func (tp *selfSignedTokenProvider) Token(context.Context) (*auth.Token, error) {
iat := now()
exp := iat.Add(time.Hour)
scope := strings.Join(tp.scopes, " ")
c := &jwt.Claims{
Iss: tp.email,
Sub: tp.email,
Aud: tp.audience,
Scope: scope,
Iat: iat.Unix(),
Exp: exp.Unix(),
}
h := &jwt.Header{
Algorithm: jwt.HeaderAlgRSA256,
Type: jwt.HeaderType,
KeyID: string(tp.pkID),
}
msg, err := jwt.EncodeJWS(h, c, tp.pk)
if err != nil {
return nil, fmt.Errorf("credentials: could not encode JWT: %w", err)
}
return &auth.Token{Value: msg, Type: internal.TokenTypeBearer, Expiry: exp}, nil
}