v4.go

// 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/internal/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.Service.Config.Credentials == credentials.AnonymousCredentials {
		return
	}

	region := req.Service.SigningRegion
	if region == "" {
		region = aws.StringValue(req.Service.Config.Region)
	}

	name := req.Service.SigningName
	if name == "" {
		name = req.Service.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.Service.Config.Credentials,
		Debug:       req.Service.Config.LogLevel.Value(),
		Logger:      req.Service.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)
}