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v4.go
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v4.go
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// Package v4 implements signing for AWS V4 signer
package v4
import (
"crypto/hmac"
"crypto/sha256"
"encoding/hex"
"fmt"
"io"
"net/http"
"net/url"
"sort"
"strconv"
"strings"
"time"
"github.com/aws/aws-sdk-go/aws"
"github.com/aws/aws-sdk-go/aws/credentials"
"github.com/aws/aws-sdk-go/aws/request"
"github.com/aws/aws-sdk-go/private/protocol/rest"
)
const (
authHeaderPrefix = "AWS4-HMAC-SHA256"
timeFormat = "20060102T150405Z"
shortTimeFormat = "20060102"
)
var ignoredHeaders = map[string]bool{
"Authorization": true,
"Content-Type": true,
"Content-Length": true,
"User-Agent": true,
}
type signer struct {
Request *http.Request
Time time.Time
ExpireTime time.Duration
ServiceName string
Region string
CredValues credentials.Value
Credentials *credentials.Credentials
Query url.Values
Body io.ReadSeeker
Debug aws.LogLevelType
Logger aws.Logger
isPresign bool
formattedTime string
formattedShortTime string
signedHeaders string
canonicalHeaders string
canonicalString string
credentialString string
stringToSign string
signature string
authorization string
}
// Sign requests with signature version 4.
//
// Will sign the requests with the service config's Credentials object
// Signing is skipped if the credentials is the credentials.AnonymousCredentials
// object.
func Sign(req *request.Request) {
// If the request does not need to be signed ignore the signing of the
// request if the AnonymousCredentials object is used.
if req.Config.Credentials == credentials.AnonymousCredentials {
return
}
region := req.ClientInfo.SigningRegion
if region == "" {
region = aws.StringValue(req.Config.Region)
}
name := req.ClientInfo.SigningName
if name == "" {
name = req.ClientInfo.ServiceName
}
s := signer{
Request: req.HTTPRequest,
Time: req.Time,
ExpireTime: req.ExpireTime,
Query: req.HTTPRequest.URL.Query(),
Body: req.Body,
ServiceName: name,
Region: region,
Credentials: req.Config.Credentials,
Debug: req.Config.LogLevel.Value(),
Logger: req.Config.Logger,
}
req.Error = s.sign()
}
func (v4 *signer) sign() error {
if v4.ExpireTime != 0 {
v4.isPresign = true
}
if v4.isRequestSigned() {
if !v4.Credentials.IsExpired() {
// If the request is already signed, and the credentials have not
// expired yet ignore the signing request.
return nil
}
// The credentials have expired for this request. The current signing
// is invalid, and needs to be request because the request will fail.
if v4.isPresign {
v4.removePresign()
// Update the request's query string to ensure the values stays in
// sync in the case retrieving the new credentials fails.
v4.Request.URL.RawQuery = v4.Query.Encode()
}
}
var err error
v4.CredValues, err = v4.Credentials.Get()
if err != nil {
return err
}
if v4.isPresign {
v4.Query.Set("X-Amz-Algorithm", authHeaderPrefix)
if v4.CredValues.SessionToken != "" {
v4.Query.Set("X-Amz-Security-Token", v4.CredValues.SessionToken)
} else {
v4.Query.Del("X-Amz-Security-Token")
}
} else if v4.CredValues.SessionToken != "" {
v4.Request.Header.Set("X-Amz-Security-Token", v4.CredValues.SessionToken)
}
v4.build()
if v4.Debug.Matches(aws.LogDebugWithSigning) {
v4.logSigningInfo()
}
return nil
}
const logSignInfoMsg = `DEBUG: Request Signiture:
---[ CANONICAL STRING ]-----------------------------
%s
---[ STRING TO SIGN ]--------------------------------
%s%s
-----------------------------------------------------`
const logSignedURLMsg = `
---[ SIGNED URL ]------------------------------------
%s`
func (v4 *signer) logSigningInfo() {
signedURLMsg := ""
if v4.isPresign {
signedURLMsg = fmt.Sprintf(logSignedURLMsg, v4.Request.URL.String())
}
msg := fmt.Sprintf(logSignInfoMsg, v4.canonicalString, v4.stringToSign, signedURLMsg)
v4.Logger.Log(msg)
}
func (v4 *signer) build() {
v4.buildTime() // no depends
v4.buildCredentialString() // no depends
if v4.isPresign {
v4.buildQuery() // no depends
}
v4.buildCanonicalHeaders() // depends on cred string
v4.buildCanonicalString() // depends on canon headers / signed headers
v4.buildStringToSign() // depends on canon string
v4.buildSignature() // depends on string to sign
if v4.isPresign {
v4.Request.URL.RawQuery += "&X-Amz-Signature=" + v4.signature
} else {
parts := []string{
authHeaderPrefix + " Credential=" + v4.CredValues.AccessKeyID + "/" + v4.credentialString,
"SignedHeaders=" + v4.signedHeaders,
"Signature=" + v4.signature,
}
v4.Request.Header.Set("Authorization", strings.Join(parts, ", "))
}
}
func (v4 *signer) buildTime() {
v4.formattedTime = v4.Time.UTC().Format(timeFormat)
v4.formattedShortTime = v4.Time.UTC().Format(shortTimeFormat)
if v4.isPresign {
duration := int64(v4.ExpireTime / time.Second)
v4.Query.Set("X-Amz-Date", v4.formattedTime)
v4.Query.Set("X-Amz-Expires", strconv.FormatInt(duration, 10))
} else {
v4.Request.Header.Set("X-Amz-Date", v4.formattedTime)
}
}
func (v4 *signer) buildCredentialString() {
v4.credentialString = strings.Join([]string{
v4.formattedShortTime,
v4.Region,
v4.ServiceName,
"aws4_request",
}, "/")
if v4.isPresign {
v4.Query.Set("X-Amz-Credential", v4.CredValues.AccessKeyID+"/"+v4.credentialString)
}
}
func (v4 *signer) buildQuery() {
for k, h := range v4.Request.Header {
if strings.HasPrefix(http.CanonicalHeaderKey(k), "X-Amz-") {
continue // never hoist x-amz-* headers, they must be signed
}
if _, ok := ignoredHeaders[http.CanonicalHeaderKey(k)]; ok {
continue // never hoist ignored headers
}
v4.Request.Header.Del(k)
v4.Query.Del(k)
for _, v := range h {
v4.Query.Add(k, v)
}
}
}
func (v4 *signer) buildCanonicalHeaders() {
var headers []string
headers = append(headers, "host")
for k := range v4.Request.Header {
if _, ok := ignoredHeaders[http.CanonicalHeaderKey(k)]; ok {
continue // ignored header
}
headers = append(headers, strings.ToLower(k))
}
sort.Strings(headers)
v4.signedHeaders = strings.Join(headers, ";")
if v4.isPresign {
v4.Query.Set("X-Amz-SignedHeaders", v4.signedHeaders)
}
headerValues := make([]string, len(headers))
for i, k := range headers {
if k == "host" {
headerValues[i] = "host:" + v4.Request.URL.Host
} else {
headerValues[i] = k + ":" +
strings.Join(v4.Request.Header[http.CanonicalHeaderKey(k)], ",")
}
}
v4.canonicalHeaders = strings.Join(headerValues, "\n")
}
func (v4 *signer) buildCanonicalString() {
v4.Request.URL.RawQuery = strings.Replace(v4.Query.Encode(), "+", "%20", -1)
uri := v4.Request.URL.Opaque
if uri != "" {
uri = "/" + strings.Join(strings.Split(uri, "/")[3:], "/")
} else {
uri = v4.Request.URL.Path
}
if uri == "" {
uri = "/"
}
if v4.ServiceName != "s3" {
uri = rest.EscapePath(uri, false)
}
v4.canonicalString = strings.Join([]string{
v4.Request.Method,
uri,
v4.Request.URL.RawQuery,
v4.canonicalHeaders + "\n",
v4.signedHeaders,
v4.bodyDigest(),
}, "\n")
}
func (v4 *signer) buildStringToSign() {
v4.stringToSign = strings.Join([]string{
authHeaderPrefix,
v4.formattedTime,
v4.credentialString,
hex.EncodeToString(makeSha256([]byte(v4.canonicalString))),
}, "\n")
}
func (v4 *signer) buildSignature() {
secret := v4.CredValues.SecretAccessKey
date := makeHmac([]byte("AWS4"+secret), []byte(v4.formattedShortTime))
region := makeHmac(date, []byte(v4.Region))
service := makeHmac(region, []byte(v4.ServiceName))
credentials := makeHmac(service, []byte("aws4_request"))
signature := makeHmac(credentials, []byte(v4.stringToSign))
v4.signature = hex.EncodeToString(signature)
}
func (v4 *signer) bodyDigest() string {
hash := v4.Request.Header.Get("X-Amz-Content-Sha256")
if hash == "" {
if v4.isPresign && v4.ServiceName == "s3" {
hash = "UNSIGNED-PAYLOAD"
} else if v4.Body == nil {
hash = hex.EncodeToString(makeSha256([]byte{}))
} else {
hash = hex.EncodeToString(makeSha256Reader(v4.Body))
}
v4.Request.Header.Add("X-Amz-Content-Sha256", hash)
}
return hash
}
// isRequestSigned returns if the request is currently signed or presigned
func (v4 *signer) isRequestSigned() bool {
if v4.isPresign && v4.Query.Get("X-Amz-Signature") != "" {
return true
}
if v4.Request.Header.Get("Authorization") != "" {
return true
}
return false
}
// unsign removes signing flags for both signed and presigned requests.
func (v4 *signer) removePresign() {
v4.Query.Del("X-Amz-Algorithm")
v4.Query.Del("X-Amz-Signature")
v4.Query.Del("X-Amz-Security-Token")
v4.Query.Del("X-Amz-Date")
v4.Query.Del("X-Amz-Expires")
v4.Query.Del("X-Amz-Credential")
v4.Query.Del("X-Amz-SignedHeaders")
}
func makeHmac(key []byte, data []byte) []byte {
hash := hmac.New(sha256.New, key)
hash.Write(data)
return hash.Sum(nil)
}
func makeSha256(data []byte) []byte {
hash := sha256.New()
hash.Write(data)
return hash.Sum(nil)
}
func makeSha256Reader(reader io.ReadSeeker) []byte {
hash := sha256.New()
start, _ := reader.Seek(0, 1)
defer reader.Seek(start, 0)
io.Copy(hash, reader)
return hash.Sum(nil)
}