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// Copyright 2021 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 (
"bytes"
"context"
"crypto/hmac"
"crypto/sha256"
"encoding/hex"
"encoding/json"
"errors"
"fmt"
"io"
"io/ioutil"
"net/http"
"net/url"
"os"
"path"
"sort"
"strings"
"time"
"golang.org/x/oauth2"
)
type awsSecurityCredentials struct {
AccessKeyID string `json:"AccessKeyID"`
SecretAccessKey string `json:"SecretAccessKey"`
SecurityToken string `json:"Token"`
}
// awsRequestSigner is a utility class to sign http requests using a AWS V4 signature.
type awsRequestSigner struct {
RegionName string
AwsSecurityCredentials awsSecurityCredentials
}
// getenv aliases os.Getenv for testing
var getenv = os.Getenv
const (
// AWS Signature Version 4 signing algorithm identifier.
awsAlgorithm = "AWS4-HMAC-SHA256"
// The termination string for the AWS credential scope value as defined in
// https://docs.aws.amazon.com/general/latest/gr/sigv4-create-string-to-sign.html
awsRequestType = "aws4_request"
// The AWS authorization header name for the security session token if available.
awsSecurityTokenHeader = "x-amz-security-token"
// The name of the header containing the session token for metadata endpoint calls
awsIMDSv2SessionTokenHeader = "X-aws-ec2-metadata-token"
awsIMDSv2SessionTtlHeader = "X-aws-ec2-metadata-token-ttl-seconds"
awsIMDSv2SessionTtl = "300"
// The AWS authorization header name for the auto-generated date.
awsDateHeader = "x-amz-date"
// Supported AWS configuration environment variables.
awsAccessKeyId = "AWS_ACCESS_KEY_ID"
awsDefaultRegion = "AWS_DEFAULT_REGION"
awsRegion = "AWS_REGION"
awsSecretAccessKey = "AWS_SECRET_ACCESS_KEY"
awsSessionToken = "AWS_SESSION_TOKEN"
awsTimeFormatLong = "20060102T150405Z"
awsTimeFormatShort = "20060102"
)
func getSha256(input []byte) (string, error) {
hash := sha256.New()
if _, err := hash.Write(input); err != nil {
return "", err
}
return hex.EncodeToString(hash.Sum(nil)), nil
}
func getHmacSha256(key, input []byte) ([]byte, error) {
hash := hmac.New(sha256.New, key)
if _, err := hash.Write(input); err != nil {
return nil, err
}
return hash.Sum(nil), nil
}
func cloneRequest(r *http.Request) *http.Request {
r2 := new(http.Request)
*r2 = *r
if r.Header != nil {
r2.Header = make(http.Header, len(r.Header))
// Find total number of values.
headerCount := 0
for _, headerValues := range r.Header {
headerCount += len(headerValues)
}
copiedHeaders := make([]string, headerCount) // shared backing array for headers' values
for headerKey, headerValues := range r.Header {
headerCount = copy(copiedHeaders, headerValues)
r2.Header[headerKey] = copiedHeaders[:headerCount:headerCount]
copiedHeaders = copiedHeaders[headerCount:]
}
}
return r2
}
func canonicalPath(req *http.Request) string {
result := req.URL.EscapedPath()
if result == "" {
return "/"
}
return path.Clean(result)
}
func canonicalQuery(req *http.Request) string {
queryValues := req.URL.Query()
for queryKey := range queryValues {
sort.Strings(queryValues[queryKey])
}
return queryValues.Encode()
}
func canonicalHeaders(req *http.Request) (string, string) {
// Header keys need to be sorted alphabetically.
var headers []string
lowerCaseHeaders := make(http.Header)
for k, v := range req.Header {
k := strings.ToLower(k)
if _, ok := lowerCaseHeaders[k]; ok {
// include additional values
lowerCaseHeaders[k] = append(lowerCaseHeaders[k], v...)
} else {
headers = append(headers, k)
lowerCaseHeaders[k] = v
}
}
sort.Strings(headers)
var fullHeaders bytes.Buffer
for _, header := range headers {
headerValue := strings.Join(lowerCaseHeaders[header], ",")
fullHeaders.WriteString(header)
fullHeaders.WriteRune(':')
fullHeaders.WriteString(headerValue)
fullHeaders.WriteRune('\n')
}
return strings.Join(headers, ";"), fullHeaders.String()
}
func requestDataHash(req *http.Request) (string, error) {
var requestData []byte
if req.Body != nil {
requestBody, err := req.GetBody()
if err != nil {
return "", err
}
defer requestBody.Close()
requestData, err = ioutil.ReadAll(io.LimitReader(requestBody, 1<<20))
if err != nil {
return "", err
}
}
return getSha256(requestData)
}
func requestHost(req *http.Request) string {
if req.Host != "" {
return req.Host
}
return req.URL.Host
}
func canonicalRequest(req *http.Request, canonicalHeaderColumns, canonicalHeaderData string) (string, error) {
dataHash, err := requestDataHash(req)
if err != nil {
return "", err
}
return fmt.Sprintf("%s\n%s\n%s\n%s\n%s\n%s", req.Method, canonicalPath(req), canonicalQuery(req), canonicalHeaderData, canonicalHeaderColumns, dataHash), nil
}
// SignRequest adds the appropriate headers to an http.Request
// or returns an error if something prevented this.
func (rs *awsRequestSigner) SignRequest(req *http.Request) error {
signedRequest := cloneRequest(req)
timestamp := now()
signedRequest.Header.Add("host", requestHost(req))
if rs.AwsSecurityCredentials.SecurityToken != "" {
signedRequest.Header.Add(awsSecurityTokenHeader, rs.AwsSecurityCredentials.SecurityToken)
}
if signedRequest.Header.Get("date") == "" {
signedRequest.Header.Add(awsDateHeader, timestamp.Format(awsTimeFormatLong))
}
authorizationCode, err := rs.generateAuthentication(signedRequest, timestamp)
if err != nil {
return err
}
signedRequest.Header.Set("Authorization", authorizationCode)
req.Header = signedRequest.Header
return nil
}
func (rs *awsRequestSigner) generateAuthentication(req *http.Request, timestamp time.Time) (string, error) {
canonicalHeaderColumns, canonicalHeaderData := canonicalHeaders(req)
dateStamp := timestamp.Format(awsTimeFormatShort)
serviceName := ""
if splitHost := strings.Split(requestHost(req), "."); len(splitHost) > 0 {
serviceName = splitHost[0]
}
credentialScope := fmt.Sprintf("%s/%s/%s/%s", dateStamp, rs.RegionName, serviceName, awsRequestType)
requestString, err := canonicalRequest(req, canonicalHeaderColumns, canonicalHeaderData)
if err != nil {
return "", err
}
requestHash, err := getSha256([]byte(requestString))
if err != nil {
return "", err
}
stringToSign := fmt.Sprintf("%s\n%s\n%s\n%s", awsAlgorithm, timestamp.Format(awsTimeFormatLong), credentialScope, requestHash)
signingKey := []byte("AWS4" + rs.AwsSecurityCredentials.SecretAccessKey)
for _, signingInput := range []string{
dateStamp, rs.RegionName, serviceName, awsRequestType, stringToSign,
} {
signingKey, err = getHmacSha256(signingKey, []byte(signingInput))
if err != nil {
return "", err
}
}
return fmt.Sprintf("%s Credential=%s/%s, SignedHeaders=%s, Signature=%s", awsAlgorithm, rs.AwsSecurityCredentials.AccessKeyID, credentialScope, canonicalHeaderColumns, hex.EncodeToString(signingKey)), nil
}
type awsCredentialSource struct {
EnvironmentID string
RegionURL string
RegionalCredVerificationURL string
CredVerificationURL string
IMDSv2SessionTokenURL string
TargetResource string
requestSigner *awsRequestSigner
region string
ctx context.Context
client *http.Client
}
type awsRequestHeader struct {
Key string `json:"key"`
Value string `json:"value"`
}
type awsRequest struct {
URL string `json:"url"`
Method string `json:"method"`
Headers []awsRequestHeader `json:"headers"`
}
func (cs awsCredentialSource) validateMetadataServers() error {
if err := cs.validateMetadataServer(cs.RegionURL, "region_url"); err != nil {
return err
}
if err := cs.validateMetadataServer(cs.CredVerificationURL, "url"); err != nil {
return err
}
return cs.validateMetadataServer(cs.IMDSv2SessionTokenURL, "imdsv2_session_token_url")
}
var validHostnames []string = []string{"169.254.169.254", "fd00:ec2::254"}
func (cs awsCredentialSource) isValidMetadataServer(metadataUrl string) bool {
if metadataUrl == "" {
// Zero value means use default, which is valid.
return true
}
u, err := url.Parse(metadataUrl)
if err != nil {
// Unparseable URL means invalid
return false
}
for _, validHostname := range validHostnames {
if u.Hostname() == validHostname {
// If it's one of the valid hostnames, everything is good
return true
}
}
// hostname not found in our allowlist, so not valid
return false
}
func (cs awsCredentialSource) validateMetadataServer(metadataUrl, urlName string) error {
if !cs.isValidMetadataServer(metadataUrl) {
return fmt.Errorf("oauth2/google: invalid hostname %s for %s", metadataUrl, urlName)
}
return nil
}
func (cs awsCredentialSource) doRequest(req *http.Request) (*http.Response, error) {
if cs.client == nil {
cs.client = oauth2.NewClient(cs.ctx, nil)
}
return cs.client.Do(req.WithContext(cs.ctx))
}
func canRetrieveRegionFromEnvironment() bool {
// The AWS region can be provided through AWS_REGION or AWS_DEFAULT_REGION. Only one is
// required.
return getenv(awsRegion) != "" || getenv(awsDefaultRegion) != ""
}
func canRetrieveSecurityCredentialFromEnvironment() bool {
// Check if both AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY are available.
return getenv(awsAccessKeyId) != "" && getenv(awsSecretAccessKey) != ""
}
func shouldUseMetadataServer() bool {
return !canRetrieveRegionFromEnvironment() || !canRetrieveSecurityCredentialFromEnvironment()
}
func (cs awsCredentialSource) subjectToken() (string, error) {
if cs.requestSigner == nil {
headers := make(map[string]string)
if shouldUseMetadataServer() {
awsSessionToken, err := cs.getAWSSessionToken()
if err != nil {
return "", err
}
if awsSessionToken != "" {
headers[awsIMDSv2SessionTokenHeader] = awsSessionToken
}
}
awsSecurityCredentials, err := cs.getSecurityCredentials(headers)
if err != nil {
return "", err
}
if cs.region, err = cs.getRegion(headers); err != nil {
return "", err
}
cs.requestSigner = &awsRequestSigner{
RegionName: cs.region,
AwsSecurityCredentials: awsSecurityCredentials,
}
}
// Generate the signed request to AWS STS GetCallerIdentity API.
// Use the required regional endpoint. Otherwise, the request will fail.
req, err := http.NewRequest("POST", strings.Replace(cs.RegionalCredVerificationURL, "{region}", cs.region, 1), nil)
if err != nil {
return "", err
}
// The full, canonical resource name of the workload identity pool
// provider, with or without the HTTPS prefix.
// Including this header as part of the signature is recommended to
// ensure data integrity.
if cs.TargetResource != "" {
req.Header.Add("x-goog-cloud-target-resource", cs.TargetResource)
}
cs.requestSigner.SignRequest(req)
/*
The GCP STS endpoint expects the headers to be formatted as:
# [
# {key: 'x-amz-date', value: '...'},
# {key: 'Authorization', value: '...'},
# ...
# ]
# And then serialized as:
# quote(json.dumps({
# url: '...',
# method: 'POST',
# headers: [{key: 'x-amz-date', value: '...'}, ...]
# }))
*/
awsSignedReq := awsRequest{
URL: req.URL.String(),
Method: "POST",
}
for headerKey, headerList := range req.Header {
for _, headerValue := range headerList {
awsSignedReq.Headers = append(awsSignedReq.Headers, awsRequestHeader{
Key: headerKey,
Value: headerValue,
})
}
}
sort.Slice(awsSignedReq.Headers, func(i, j int) bool {
headerCompare := strings.Compare(awsSignedReq.Headers[i].Key, awsSignedReq.Headers[j].Key)
if headerCompare == 0 {
return strings.Compare(awsSignedReq.Headers[i].Value, awsSignedReq.Headers[j].Value) < 0
}
return headerCompare < 0
})
result, err := json.Marshal(awsSignedReq)
if err != nil {
return "", err
}
return url.QueryEscape(string(result)), nil
}
func (cs *awsCredentialSource) getAWSSessionToken() (string, error) {
if cs.IMDSv2SessionTokenURL == "" {
return "", nil
}
req, err := http.NewRequest("PUT", cs.IMDSv2SessionTokenURL, nil)
if err != nil {
return "", err
}
req.Header.Add(awsIMDSv2SessionTtlHeader, awsIMDSv2SessionTtl)
resp, err := cs.doRequest(req)
if err != nil {
return "", err
}
defer resp.Body.Close()
respBody, err := ioutil.ReadAll(io.LimitReader(resp.Body, 1<<20))
if err != nil {
return "", err
}
if resp.StatusCode != 200 {
return "", fmt.Errorf("oauth2/google: unable to retrieve AWS session token - %s", string(respBody))
}
return string(respBody), nil
}
func (cs *awsCredentialSource) getRegion(headers map[string]string) (string, error) {
if canRetrieveRegionFromEnvironment() {
if envAwsRegion := getenv(awsRegion); envAwsRegion != "" {
return envAwsRegion, nil
}
return getenv("AWS_DEFAULT_REGION"), nil
}
if cs.RegionURL == "" {
return "", errors.New("oauth2/google: unable to determine AWS region")
}
req, err := http.NewRequest("GET", cs.RegionURL, nil)
if err != nil {
return "", err
}
for name, value := range headers {
req.Header.Add(name, value)
}
resp, err := cs.doRequest(req)
if err != nil {
return "", err
}
defer resp.Body.Close()
respBody, err := ioutil.ReadAll(io.LimitReader(resp.Body, 1<<20))
if err != nil {
return "", err
}
if resp.StatusCode != 200 {
return "", fmt.Errorf("oauth2/google: unable to retrieve AWS region - %s", string(respBody))
}
// This endpoint will return the region in format: us-east-2b.
// Only the us-east-2 part should be used.
respBodyEnd := 0
if len(respBody) > 1 {
respBodyEnd = len(respBody) - 1
}
return string(respBody[:respBodyEnd]), nil
}
func (cs *awsCredentialSource) getSecurityCredentials(headers map[string]string) (result awsSecurityCredentials, err error) {
if canRetrieveSecurityCredentialFromEnvironment() {
return awsSecurityCredentials{
AccessKeyID: getenv(awsAccessKeyId),
SecretAccessKey: getenv(awsSecretAccessKey),
SecurityToken: getenv(awsSessionToken),
}, nil
}
roleName, err := cs.getMetadataRoleName(headers)
if err != nil {
return
}
credentials, err := cs.getMetadataSecurityCredentials(roleName, headers)
if err != nil {
return
}
if credentials.AccessKeyID == "" {
return result, errors.New("oauth2/google: missing AccessKeyId credential")
}
if credentials.SecretAccessKey == "" {
return result, errors.New("oauth2/google: missing SecretAccessKey credential")
}
return credentials, nil
}
func (cs *awsCredentialSource) getMetadataSecurityCredentials(roleName string, headers map[string]string) (awsSecurityCredentials, error) {
var result awsSecurityCredentials
req, err := http.NewRequest("GET", fmt.Sprintf("%s/%s", cs.CredVerificationURL, roleName), nil)
if err != nil {
return result, err
}
req.Header.Add("Content-Type", "application/json")
for name, value := range headers {
req.Header.Add(name, value)
}
resp, err := cs.doRequest(req)
if err != nil {
return result, err
}
defer resp.Body.Close()
respBody, err := ioutil.ReadAll(io.LimitReader(resp.Body, 1<<20))
if err != nil {
return result, err
}
if resp.StatusCode != 200 {
return result, fmt.Errorf("oauth2/google: unable to retrieve AWS security credentials - %s", string(respBody))
}
err = json.Unmarshal(respBody, &result)
return result, err
}
func (cs *awsCredentialSource) getMetadataRoleName(headers map[string]string) (string, error) {
if cs.CredVerificationURL == "" {
return "", errors.New("oauth2/google: unable to determine the AWS metadata server security credentials endpoint")
}
req, err := http.NewRequest("GET", cs.CredVerificationURL, nil)
if err != nil {
return "", err
}
for name, value := range headers {
req.Header.Add(name, value)
}
resp, err := cs.doRequest(req)
if err != nil {
return "", err
}
defer resp.Body.Close()
respBody, err := ioutil.ReadAll(io.LimitReader(resp.Body, 1<<20))
if err != nil {
return "", err
}
if resp.StatusCode != 200 {
return "", fmt.Errorf("oauth2/google: unable to retrieve AWS role name - %s", string(respBody))
}
return string(respBody), nil
}