google: support AWS 3rd party credentials

Change-Id: I655b38f7fb8023866bb284c7ce80ab9888682e73
GitHub-Last-Rev: 648f0b3
GitHub-Pull-Request: #471
Reviewed-on: https://go-review.googlesource.com/c/oauth2/+/287752
Reviewed-by: Cody Oss <codyoss@google.com>
Run-TryBot: Cody Oss <codyoss@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Tyler Bui-Palsulich <tbp@google.com>
Trust: Cody Oss <codyoss@google.com>

Author: Ryan Kohler

google/internal/externalaccount/aws.go

@@ -5,41 +5,54 @@
 package externalaccount
 
 import (
+	"context"
 	"crypto/hmac"
 	"crypto/sha256"
 	"encoding/hex"
+	"encoding/json"
 	"errors"
 	"fmt"
+	"golang.org/x/oauth2"
 	"io"
 	"io/ioutil"
 	"net/http"
+	"os"
 	"path"
 	"sort"
 	"strings"
 	"time"
 )
 
-// RequestSigner is a utility class to sign http requests using a AWS V4 signature.
+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 map[string]string
+	AwsSecurityCredentials awsSecurityCredentials
 }
 
+// getenv aliases os.Getenv for testing
+var getenv = os.Getenv
+
 const (
-// AWS Signature Version 4 signing algorithm identifier.
+	// 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
+	// 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.
+	// The AWS authorization header name for the security session token if available.
 	awsSecurityTokenHeader = "x-amz-security-token"
 
-// The AWS authorization header name for the auto-generated date.
+	// The AWS authorization header name for the auto-generated date.
 	awsDateHeader = "x-amz-date"
 
-	awsTimeFormatLong = "20060102T150405Z"
+	awsTimeFormatLong  = "20060102T150405Z"
 	awsTimeFormatShort = "20060102"
 )
 
@@ -167,8 +180,8 @@ func (rs *awsRequestSigner) SignRequest(req *http.Request) error {
 
 	signedRequest.Header.Add("host", requestHost(req))
 
-	if securityToken, ok := rs.AwsSecurityCredentials["security_token"]; ok {
-		signedRequest.Header.Add(awsSecurityTokenHeader, securityToken)
+	if rs.AwsSecurityCredentials.SecurityToken != "" {
+		signedRequest.Header.Add(awsSecurityTokenHeader, rs.AwsSecurityCredentials.SecurityToken)
 	}
 
 	if signedRequest.Header.Get("date") == "" {
@@ -186,15 +199,6 @@ func (rs *awsRequestSigner) SignRequest(req *http.Request) error {
 }
 
 func (rs *awsRequestSigner) generateAuthentication(req *http.Request, timestamp time.Time) (string, error) {
-	secretAccessKey, ok := rs.AwsSecurityCredentials["secret_access_key"]
-	if !ok {
-		return "", errors.New("oauth2/google: missing secret_access_key header")
-	}
-	accessKeyId, ok := rs.AwsSecurityCredentials["access_key_id"]
-	if !ok {
-		return "", errors.New("oauth2/google: missing access_key_id header")
-	}
-
 	canonicalHeaderColumns, canonicalHeaderData := canonicalHeaders(req)
 
 	dateStamp := timestamp.Format(awsTimeFormatShort)
@@ -203,28 +207,258 @@ func (rs *awsRequestSigner) generateAuthentication(req *http.Request, timestamp
 		serviceName = splitHost[0]
 	}
 
-	credentialScope := fmt.Sprintf("%s/%s/%s/%s",dateStamp, rs.RegionName, serviceName, awsRequestType)
+	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{
+	if err != nil {
 		return "", err
 	}
 
 	stringToSign := fmt.Sprintf("%s\n%s\n%s\n%s", awsAlgorithm, timestamp.Format(awsTimeFormatLong), credentialScope, requestHash)
 
-	signingKey := []byte("AWS4" + secretAccessKey)
+	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{
+		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
+	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) 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 (cs awsCredentialSource) subjectToken() (string, error) {
+	if cs.requestSigner == nil {
+		awsSecurityCredentials, err := cs.getSecurityCredentials()
+		if err != nil {
 			return "", err
 		}
+
+		if cs.region, err = cs.getRegion(); 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 string(result), nil
+}
+
+func (cs *awsCredentialSource) getRegion() (string, error) {
+	if envAwsRegion := getenv("AWS_REGION"); envAwsRegion != "" {
+		return envAwsRegion, 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
+	}
+
+	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() (result awsSecurityCredentials, err error) {
+	if accessKeyID := getenv("AWS_ACCESS_KEY_ID"); accessKeyID != "" {
+		if secretAccessKey := getenv("AWS_SECRET_ACCESS_KEY"); secretAccessKey != "" {
+			return awsSecurityCredentials{
+				AccessKeyID:     accessKeyID,
+				SecretAccessKey: secretAccessKey,
+				SecurityToken:   getenv("AWS_SESSION_TOKEN"),
+			}, nil
+		}
+	}
+
+	roleName, err := cs.getMetadataRoleName()
+	if err != nil {
+		return
+	}
+
+	credentials, err := cs.getMetadataSecurityCredentials(roleName)
+	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) (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")
+
+	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() (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
+	}
+
+	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 fmt.Sprintf("%s Credential=%s/%s, SignedHeaders=%s, Signature=%s", awsAlgorithm, accessKeyId, credentialScope, canonicalHeaderColumns, hex.EncodeToString(signingKey)), nil
+	return string(respBody), nil
 }