forked from TrueCloudLab/distribution
127 lines
3.8 KiB
Go
127 lines
3.8 KiB
Go
// Copyright 2020 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package impersonate is used to impersonate Google Credentials.
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package impersonate
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import (
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"bytes"
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"context"
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"encoding/json"
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"fmt"
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"io"
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"net/http"
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"time"
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"golang.org/x/oauth2"
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)
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// Config for generating impersonated credentials.
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type Config struct {
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// Target is the service account to impersonate. Required.
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Target string
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// Scopes the impersonated credential should have. Required.
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Scopes []string
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// Delegates are the service accounts in a delegation chain. Each service
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// account must be granted roles/iam.serviceAccountTokenCreator on the next
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// service account in the chain. Optional.
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Delegates []string
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}
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// TokenSource returns an impersonated TokenSource configured with the provided
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// config using ts as the base credential provider for making requests.
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func TokenSource(ctx context.Context, ts oauth2.TokenSource, config *Config) (oauth2.TokenSource, error) {
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if len(config.Scopes) == 0 {
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return nil, fmt.Errorf("impersonate: scopes must be provided")
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}
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its := impersonatedTokenSource{
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ctx: ctx,
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ts: ts,
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name: formatIAMServiceAccountName(config.Target),
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// Default to the longest acceptable value of one hour as the token will
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// be refreshed automatically.
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lifetime: "3600s",
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}
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its.delegates = make([]string, len(config.Delegates))
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for i, v := range config.Delegates {
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its.delegates[i] = formatIAMServiceAccountName(v)
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}
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its.scopes = make([]string, len(config.Scopes))
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copy(its.scopes, config.Scopes)
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return oauth2.ReuseTokenSource(nil, its), nil
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}
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func formatIAMServiceAccountName(name string) string {
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return fmt.Sprintf("projects/-/serviceAccounts/%s", name)
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}
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type generateAccessTokenReq struct {
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Delegates []string `json:"delegates,omitempty"`
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Lifetime string `json:"lifetime,omitempty"`
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Scope []string `json:"scope,omitempty"`
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}
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type generateAccessTokenResp struct {
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AccessToken string `json:"accessToken"`
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ExpireTime string `json:"expireTime"`
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}
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type impersonatedTokenSource struct {
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ctx context.Context
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ts oauth2.TokenSource
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name string
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lifetime string
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scopes []string
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delegates []string
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}
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// Token returns an impersonated Token.
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func (i impersonatedTokenSource) Token() (*oauth2.Token, error) {
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hc := oauth2.NewClient(i.ctx, i.ts)
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reqBody := generateAccessTokenReq{
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Delegates: i.delegates,
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Lifetime: i.lifetime,
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Scope: i.scopes,
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}
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b, err := json.Marshal(reqBody)
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if err != nil {
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return nil, fmt.Errorf("impersonate: unable to marshal request: %v", err)
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}
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url := fmt.Sprintf("https://iamcredentials.googleapis.com/v1/%s:generateAccessToken", i.name)
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req, err := http.NewRequest("POST", url, bytes.NewReader(b))
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if err != nil {
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return nil, fmt.Errorf("impersonate: unable to create request: %v", err)
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}
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req = req.WithContext(i.ctx)
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req.Header.Set("Content-Type", "application/json")
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resp, err := hc.Do(req)
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if err != nil {
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return nil, fmt.Errorf("impersonate: unable to generate access token: %v", err)
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}
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defer resp.Body.Close()
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body, err := io.ReadAll(io.LimitReader(resp.Body, 1<<20))
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if err != nil {
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return nil, fmt.Errorf("impersonate: unable to read body: %v", err)
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}
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if c := resp.StatusCode; c < 200 || c > 299 {
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return nil, fmt.Errorf("impersonate: status code %d: %s", c, body)
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}
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var accessTokenResp generateAccessTokenResp
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if err := json.Unmarshal(body, &accessTokenResp); err != nil {
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return nil, fmt.Errorf("impersonate: unable to parse response: %v", err)
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}
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expiry, err := time.Parse(time.RFC3339, accessTokenResp.ExpireTime)
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if err != nil {
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return nil, fmt.Errorf("impersonate: unable to parse expiry: %v", err)
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}
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return &oauth2.Token{
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AccessToken: accessTokenResp.AccessToken,
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Expiry: expiry,
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}, nil
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}
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