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// Copyright 2020 Google LLC.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package idtoken
import (
"context"
"encoding/json"
"fmt"
"net/http"
"cloud.google.com/go/compute/metadata"
"golang.org/x/oauth2"
"golang.org/x/oauth2/google"
"google.golang.org/api/internal"
"google.golang.org/api/option"
"google.golang.org/api/option/internaloption"
htransport "google.golang.org/api/transport/http"
)
// ClientOption is aliased so relevant options are easily found in the docs.
// ClientOption is for configuring a Google API client or transport.
type ClientOption = option.ClientOption
// NewClient creates a HTTP Client that automatically adds an ID token to each
// request via an Authorization header. The token will have have the audience
// provided and be configured with the supplied options. The parameter audience
// may not be empty.
func NewClient(ctx context.Context, audience string, opts ...ClientOption) (*http.Client, error) {
var ds internal.DialSettings
for _, opt := range opts {
opt.Apply(&ds)
}
if err := ds.Validate(); err != nil {
return nil, err
}
if ds.NoAuth {
return nil, fmt.Errorf("idtoken: option.WithoutAuthentication not supported")
}
if ds.APIKey != "" {
return nil, fmt.Errorf("idtoken: option.WithAPIKey not supported")
}
if ds.TokenSource != nil {
return nil, fmt.Errorf("idtoken: option.WithTokenSource not supported")
}
ts, err := NewTokenSource(ctx, audience, opts...)
if err != nil {
return nil, err
}
// Skip DialSettings validation so added TokenSource will not conflict with user
// provided credentials.
opts = append(opts, option.WithTokenSource(ts), internaloption.SkipDialSettingsValidation())
t, err := htransport.NewTransport(ctx, http.DefaultTransport, opts...)
if err != nil {
return nil, err
}
return &http.Client{Transport: t}, nil
}
// NewTokenSource creates a TokenSource that returns ID tokens with the audience
// provided and configured with the supplied options. The parameter audience may
// not be empty.
func NewTokenSource(ctx context.Context, audience string, opts ...ClientOption) (oauth2.TokenSource, error) {
if audience == "" {
return nil, fmt.Errorf("idtoken: must supply a non-empty audience")
}
var ds internal.DialSettings
for _, opt := range opts {
opt.Apply(&ds)
}
if err := ds.Validate(); err != nil {
return nil, err
}
if ds.TokenSource != nil {
return nil, fmt.Errorf("idtoken: option.WithTokenSource not supported")
}
if ds.ImpersonationConfig != nil {
return nil, fmt.Errorf("idtoken: option.WithImpersonatedCredentials not supported")
}
return newTokenSource(ctx, audience, &ds)
}
func newTokenSource(ctx context.Context, audience string, ds *internal.DialSettings) (oauth2.TokenSource, error) {
creds, err := internal.Creds(ctx, ds)
if err != nil {
return nil, err
}
if len(creds.JSON) > 0 {
return tokenSourceFromBytes(ctx, creds.JSON, audience, ds)
}
// If internal.Creds did not return a response with JSON fallback to the
// metadata service as the creds.TokenSource is not an ID token.
if metadata.OnGCE() {
return computeTokenSource(audience, ds)
}
return nil, fmt.Errorf("idtoken: couldn't find any credentials")
}
func tokenSourceFromBytes(ctx context.Context, data []byte, audience string, ds *internal.DialSettings) (oauth2.TokenSource, error) {
if err := isServiceAccount(data); err != nil {
return nil, err
}
cfg, err := google.JWTConfigFromJSON(data, ds.GetScopes()...)
if err != nil {
return nil, err
}
customClaims := ds.CustomClaims
if customClaims == nil {
customClaims = make(map[string]interface{})
}
customClaims["target_audience"] = audience
cfg.PrivateClaims = customClaims
cfg.UseIDToken = true
ts := cfg.TokenSource(ctx)
tok, err := ts.Token()
if err != nil {
return nil, err
}
return oauth2.ReuseTokenSource(tok, ts), nil
}
func isServiceAccount(data []byte) error {
if len(data) == 0 {
return fmt.Errorf("idtoken: credential provided is 0 bytes")
}
var f struct {
Type string `json:"type"`
}
if err := json.Unmarshal(data, &f); err != nil {
return err
}
if f.Type != "service_account" {
return fmt.Errorf("idtoken: credential must be service_account, found %q", f.Type)
}
return nil
}
// WithCustomClaims optionally specifies custom private claims for an ID token.
func WithCustomClaims(customClaims map[string]interface{}) ClientOption {
return withCustomClaims(customClaims)
}
type withCustomClaims map[string]interface{}
func (w withCustomClaims) Apply(o *internal.DialSettings) {
o.CustomClaims = w
}
// WithCredentialsFile returns a ClientOption that authenticates
// API calls with the given service account or refresh token JSON
// credentials file.
func WithCredentialsFile(filename string) ClientOption {
return option.WithCredentialsFile(filename)
}
// WithCredentialsJSON returns a ClientOption that authenticates
// API calls with the given service account or refresh token JSON
// credentials.
func WithCredentialsJSON(p []byte) ClientOption {
return option.WithCredentialsJSON(p)
}
// WithHTTPClient returns a ClientOption that specifies the HTTP client to use
// as the basis of communications. This option may only be used with services
// that support HTTP as their communication transport. When used, the
// WithHTTPClient option takes precedent over all other supplied options.
func WithHTTPClient(client *http.Client) ClientOption {
return option.WithHTTPClient(client)
}
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