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// Copyright 2020 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package externalaccount
import (
"context"
"encoding/json"
"fmt"
"io"
"io/ioutil"
"net/http"
"net/url"
"strconv"
"strings"
"golang.org/x/oauth2"
)
// exchangeToken performs an oauth2 token exchange with the provided endpoint.
// The first 4 fields are all mandatory. headers can be used to pass additional
// headers beyond the bare minimum required by the token exchange. options can
// be used to pass additional JSON-structured options to the remote server.
func exchangeToken(ctx context.Context, endpoint string, request *stsTokenExchangeRequest, authentication clientAuthentication, headers http.Header, options map[string]interface{}) (*stsTokenExchangeResponse, error) {
client := oauth2.NewClient(ctx, nil)
data := url.Values{}
data.Set("audience", request.Audience)
data.Set("grant_type", "urn:ietf:params:oauth:grant-type:token-exchange")
data.Set("requested_token_type", "urn:ietf:params:oauth:token-type:access_token")
data.Set("subject_token_type", request.SubjectTokenType)
data.Set("subject_token", request.SubjectToken)
data.Set("scope", strings.Join(request.Scope, " "))
if options != nil {
opts, err := json.Marshal(options)
if err != nil {
return nil, fmt.Errorf("oauth2/google: failed to marshal additional options: %v", err)
}
data.Set("options", string(opts))
}
authentication.InjectAuthentication(data, headers)
encodedData := data.Encode()
req, err := http.NewRequest("POST", endpoint, strings.NewReader(encodedData))
if err != nil {
return nil, fmt.Errorf("oauth2/google: failed to properly build http request: %v", err)
}
req = req.WithContext(ctx)
for key, list := range headers {
for _, val := range list {
req.Header.Add(key, val)
}
}
req.Header.Add("Content-Length", strconv.Itoa(len(encodedData)))
resp, err := client.Do(req)
if err != nil {
return nil, fmt.Errorf("oauth2/google: invalid response from Secure Token Server: %v", err)
}
defer resp.Body.Close()
body, err := ioutil.ReadAll(io.LimitReader(resp.Body, 1<<20))
if err != nil {
return nil, err
}
if c := resp.StatusCode; c < 200 || c > 299 {
return nil, fmt.Errorf("oauth2/google: status code %d: %s", c, body)
}
var stsResp stsTokenExchangeResponse
err = json.Unmarshal(body, &stsResp)
if err != nil {
return nil, fmt.Errorf("oauth2/google: failed to unmarshal response body from Secure Token Server: %v", err)
}
return &stsResp, nil
}
// stsTokenExchangeRequest contains fields necessary to make an oauth2 token exchange.
type stsTokenExchangeRequest struct {
ActingParty struct {
ActorToken string
ActorTokenType string
}
GrantType string
Resource string
Audience string
Scope []string
RequestedTokenType string
SubjectToken string
SubjectTokenType string
}
// stsTokenExchangeResponse is used to decode the remote server response during an oauth2 token exchange.
type stsTokenExchangeResponse struct {
AccessToken string `json:"access_token"`
IssuedTokenType string `json:"issued_token_type"`
TokenType string `json:"token_type"`
ExpiresIn int `json:"expires_in"`
Scope string `json:"scope"`
RefreshToken string `json:"refresh_token"`
}
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