diff --git a/google/internal/externalaccount/aws.go b/google/internal/externalaccount/aws.go
new file mode 100644
index 0000000..906d1fe
--- /dev/null
+++ b/google/internal/externalaccount/aws.go
@@ -0,0 +1,230 @@
+// 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 (
+	"crypto/hmac"
+	"crypto/sha256"
+	"encoding/hex"
+	"errors"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"net/http"
+	"path"
+	"sort"
+	"strings"
+	"time"
+)
+
+// RequestSigner is a utility class to sign http requests using a AWS V4 signature.
+type awsRequestSigner struct {
+	RegionName             string
+	AwsSecurityCredentials map[string]string
+}
+
+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 AWS authorization header name for the auto-generated date.
+	awsDateHeader = "x-amz-date"
+
+	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 strings.Builder
+	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 securityToken, ok := rs.AwsSecurityCredentials["security_token"]; ok {
+		signedRequest.Header.Add(awsSecurityTokenHeader, 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) {
+	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)
+	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" + 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, accessKeyId, credentialScope, canonicalHeaderColumns, hex.EncodeToString(signingKey)), nil
+}
diff --git a/google/internal/externalaccount/aws_test.go b/google/internal/externalaccount/aws_test.go
new file mode 100644
index 0000000..206c3a1
--- /dev/null
+++ b/google/internal/externalaccount/aws_test.go
@@ -0,0 +1,396 @@
+// 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 (
+	"net/http"
+	"reflect"
+	"strings"
+	"testing"
+	"time"
+)
+
+var defaultTime = time.Date(2011, 9, 9, 23, 36, 0, 0, time.UTC)
+var secondDefaultTime = time.Date(2020, 8, 11, 6, 55, 22, 0, time.UTC)
+
+func setTime(testTime time.Time) func() time.Time {
+	return func() time.Time {
+		return testTime
+	}
+}
+
+var defaultRequestSigner = &awsRequestSigner{
+	RegionName: "us-east-1",
+	AwsSecurityCredentials: map[string]string{
+		"access_key_id":     "AKIDEXAMPLE",
+		"secret_access_key": "wJalrXUtnFEMI/K7MDENG+bPxRfiCYEXAMPLEKEY",
+	},
+}
+
+const accessKeyId = "ASIARD4OQDT6A77FR3CL"
+const secretAccessKey = "Y8AfSaucF37G4PpvfguKZ3/l7Id4uocLXxX0+VTx"
+const securityToken = "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"
+
+var requestSignerWithToken = &awsRequestSigner{
+	RegionName: "us-east-2",
+	AwsSecurityCredentials: map[string]string{
+		"access_key_id":     accessKeyId,
+		"secret_access_key": secretAccessKey,
+		"security_token":    securityToken,
+	},
+}
+
+func setDefaultTime(req *http.Request) {
+	// Don't use time.Format for this
+	// Our output signature expects this to be a Monday, even though Sept 9, 2011 is a Friday
+	req.Header.Add("date", "Mon, 09 Sep 2011 23:36:00 GMT")
+}
+
+func testRequestSigner(t *testing.T, rs *awsRequestSigner, input, expectedOutput *http.Request) {
+	t.Helper()
+
+	err := rs.SignRequest(input)
+	if err != nil {
+		t.Errorf("unexpected error: %q", err.Error())
+	}
+
+	if got, want := input.URL.String(), expectedOutput.URL.String(); !reflect.DeepEqual(got, want) {
+		t.Errorf("url = %q, want %q", got, want)
+	}
+	if got, want := input.Method, expectedOutput.Method; !reflect.DeepEqual(got, want) {
+		t.Errorf("method = %q, want %q", got, want)
+	}
+	for header := range expectedOutput.Header {
+		if got, want := input.Header[header], expectedOutput.Header[header]; !reflect.DeepEqual(got, want) {
+			t.Errorf("header[%q] = %q, want %q", header, got, want)
+		}
+	}
+}
+
+func TestAwsV4Signature_GetRequest(t *testing.T) {
+	input, _ := http.NewRequest("GET", "https://host.foo.com", nil)
+	setDefaultTime(input)
+
+	output, _ := http.NewRequest("GET", "https://host.foo.com", nil)
+	output.Header = http.Header{
+		"Host":          []string{"host.foo.com"},
+		"Date":          []string{"Mon, 09 Sep 2011 23:36:00 GMT"},
+		"Authorization": []string{"AWS4-HMAC-SHA256 Credential=AKIDEXAMPLE/20110909/us-east-1/host/aws4_request, SignedHeaders=date;host, Signature=b27ccfbfa7df52a200ff74193ca6e32d4b48b8856fab7ebf1c595d0670a7e470"},
+	}
+
+	oldNow := now
+	defer func() { now = oldNow }()
+	now = setTime(defaultTime)
+
+	testRequestSigner(t, defaultRequestSigner, input, output)
+}
+
+func TestAwsV4Signature_GetRequestWithRelativePath(t *testing.T) {
+	input, _ := http.NewRequest("GET", "https://host.foo.com/foo/bar/../..", nil)
+	setDefaultTime(input)
+
+	output, _ := http.NewRequest("GET", "https://host.foo.com/foo/bar/../..", nil)
+	output.Header = http.Header{
+		"Host":          []string{"host.foo.com"},
+		"Date":          []string{"Mon, 09 Sep 2011 23:36:00 GMT"},
+		"Authorization": []string{"AWS4-HMAC-SHA256 Credential=AKIDEXAMPLE/20110909/us-east-1/host/aws4_request, SignedHeaders=date;host, Signature=b27ccfbfa7df52a200ff74193ca6e32d4b48b8856fab7ebf1c595d0670a7e470"},
+	}
+
+	oldNow := now
+	defer func() { now = oldNow }()
+	now = setTime(defaultTime)
+
+	testRequestSigner(t, defaultRequestSigner, input, output)
+}
+
+func TestAwsV4Signature_GetRequestWithDotPath(t *testing.T) {
+	input, _ := http.NewRequest("GET", "https://host.foo.com/./", nil)
+	setDefaultTime(input)
+
+	output, _ := http.NewRequest("GET", "https://host.foo.com/./", nil)
+	output.Header = http.Header{
+		"Host":          []string{"host.foo.com"},
+		"Date":          []string{"Mon, 09 Sep 2011 23:36:00 GMT"},
+		"Authorization": []string{"AWS4-HMAC-SHA256 Credential=AKIDEXAMPLE/20110909/us-east-1/host/aws4_request, SignedHeaders=date;host, Signature=b27ccfbfa7df52a200ff74193ca6e32d4b48b8856fab7ebf1c595d0670a7e470"},
+	}
+
+	oldNow := now
+	defer func() { now = oldNow }()
+	now = setTime(defaultTime)
+
+	testRequestSigner(t, defaultRequestSigner, input, output)
+}
+
+func TestAwsV4Signature_GetRequestWithPointlessDotPath(t *testing.T) {
+	input, _ := http.NewRequest("GET", "https://host.foo.com/./foo", nil)
+	setDefaultTime(input)
+
+	output, _ := http.NewRequest("GET", "https://host.foo.com/./foo", nil)
+	output.Header = http.Header{
+		"Host":          []string{"host.foo.com"},
+		"Date":          []string{"Mon, 09 Sep 2011 23:36:00 GMT"},
+		"Authorization": []string{"AWS4-HMAC-SHA256 Credential=AKIDEXAMPLE/20110909/us-east-1/host/aws4_request, SignedHeaders=date;host, Signature=910e4d6c9abafaf87898e1eb4c929135782ea25bb0279703146455745391e63a"},
+	}
+
+	oldNow := now
+	defer func() { now = oldNow }()
+	now = setTime(defaultTime)
+
+	testRequestSigner(t, defaultRequestSigner, input, output)
+}
+
+func TestAwsV4Signature_GetRequestWithUtf8Path(t *testing.T) {
+	input, _ := http.NewRequest("GET", "https://host.foo.com/%E1%88%B4", nil)
+	setDefaultTime(input)
+
+	output, _ := http.NewRequest("GET", "https://host.foo.com/%E1%88%B4", nil)
+	output.Header = http.Header{
+		"Host":          []string{"host.foo.com"},
+		"Date":          []string{"Mon, 09 Sep 2011 23:36:00 GMT"},
+		"Authorization": []string{"AWS4-HMAC-SHA256 Credential=AKIDEXAMPLE/20110909/us-east-1/host/aws4_request, SignedHeaders=date;host, Signature=8d6634c189aa8c75c2e51e106b6b5121bed103fdb351f7d7d4381c738823af74"},
+	}
+
+	oldNow := now
+	defer func() { now = oldNow }()
+	now = setTime(defaultTime)
+
+	testRequestSigner(t, defaultRequestSigner, input, output)
+}
+
+func TestAwsV4Signature_GetRequestWithDuplicateQuery(t *testing.T) {
+	input, _ := http.NewRequest("GET", "https://host.foo.com/?foo=Zoo&foo=aha", nil)
+	setDefaultTime(input)
+
+	output, _ := http.NewRequest("GET", "https://host.foo.com/?foo=Zoo&foo=aha", nil)
+	output.Header = http.Header{
+		"Host":          []string{"host.foo.com"},
+		"Date":          []string{"Mon, 09 Sep 2011 23:36:00 GMT"},
+		"Authorization": []string{"AWS4-HMAC-SHA256 Credential=AKIDEXAMPLE/20110909/us-east-1/host/aws4_request, SignedHeaders=date;host, Signature=be7148d34ebccdc6423b19085378aa0bee970bdc61d144bd1a8c48c33079ab09"},
+	}
+
+	oldNow := now
+	defer func() { now = oldNow }()
+	now = setTime(defaultTime)
+
+	testRequestSigner(t, defaultRequestSigner, input, output)
+}
+
+func TestAwsV4Signature_GetRequestWithMisorderedQuery(t *testing.T) {
+	input, _ := http.NewRequest("GET", "https://host.foo.com/?foo=b&foo=a", nil)
+	setDefaultTime(input)
+
+	output, _ := http.NewRequest("GET", "https://host.foo.com/?foo=b&foo=a", nil)
+	output.Header = http.Header{
+		"Host":          []string{"host.foo.com"},
+		"Date":          []string{"Mon, 09 Sep 2011 23:36:00 GMT"},
+		"Authorization": []string{"AWS4-HMAC-SHA256 Credential=AKIDEXAMPLE/20110909/us-east-1/host/aws4_request, SignedHeaders=date;host, Signature=feb926e49e382bec75c9d7dcb2a1b6dc8aa50ca43c25d2bc51143768c0875acc"},
+	}
+
+	oldNow := now
+	defer func() { now = oldNow }()
+	now = setTime(defaultTime)
+
+	testRequestSigner(t, defaultRequestSigner, input, output)
+}
+
+func TestAwsV4Signature_GetRequestWithUtf8Query(t *testing.T) {
+	input, _ := http.NewRequest("GET", "https://host.foo.com/?ሴ=bar", nil)
+	setDefaultTime(input)
+
+	output, _ := http.NewRequest("GET", "https://host.foo.com/?ሴ=bar", nil)
+	output.Header = http.Header{
+		"Host":          []string{"host.foo.com"},
+		"Date":          []string{"Mon, 09 Sep 2011 23:36:00 GMT"},
+		"Authorization": []string{"AWS4-HMAC-SHA256 Credential=AKIDEXAMPLE/20110909/us-east-1/host/aws4_request, SignedHeaders=date;host, Signature=6fb359e9a05394cc7074e0feb42573a2601abc0c869a953e8c5c12e4e01f1a8c"},
+	}
+
+	oldNow := now
+	defer func() { now = oldNow }()
+	now = setTime(defaultTime)
+
+	testRequestSigner(t, defaultRequestSigner, input, output)
+}
+
+func TestAwsV4Signature_PostRequest(t *testing.T) {
+	input, _ := http.NewRequest("POST", "https://host.foo.com/", nil)
+	setDefaultTime(input)
+	input.Header.Add("ZOO", "zoobar")
+
+	output, _ := http.NewRequest("POST", "https://host.foo.com/", nil)
+	output.Header = http.Header{
+		"Host":          []string{"host.foo.com"},
+		"Date":          []string{"Mon, 09 Sep 2011 23:36:00 GMT"},
+		"Authorization": []string{"AWS4-HMAC-SHA256 Credential=AKIDEXAMPLE/20110909/us-east-1/host/aws4_request, SignedHeaders=date;host;zoo, Signature=b7a95a52518abbca0964a999a880429ab734f35ebbf1235bd79a5de87756dc4a"},
+		"Zoo":           []string{"zoobar"},
+	}
+
+	oldNow := now
+	defer func() { now = oldNow }()
+	now = setTime(defaultTime)
+
+	testRequestSigner(t, defaultRequestSigner, input, output)
+}
+
+func TestAwsV4Signature_PostRequestWithCapitalizedHeaderValue(t *testing.T) {
+	input, _ := http.NewRequest("POST", "https://host.foo.com/", nil)
+	setDefaultTime(input)
+	input.Header.Add("zoo", "ZOOBAR")
+
+	output, _ := http.NewRequest("POST", "https://host.foo.com/", nil)
+	output.Header = http.Header{
+		"Host":          []string{"host.foo.com"},
+		"Date":          []string{"Mon, 09 Sep 2011 23:36:00 GMT"},
+		"Authorization": []string{"AWS4-HMAC-SHA256 Credential=AKIDEXAMPLE/20110909/us-east-1/host/aws4_request, SignedHeaders=date;host;zoo, Signature=273313af9d0c265c531e11db70bbd653f3ba074c1009239e8559d3987039cad7"},
+		"Zoo":           []string{"ZOOBAR"},
+	}
+
+	oldNow := now
+	defer func() { now = oldNow }()
+	now = setTime(defaultTime)
+
+	testRequestSigner(t, defaultRequestSigner, input, output)
+}
+
+func TestAwsV4Signature_PostRequestPhfft(t *testing.T) {
+	input, _ := http.NewRequest("POST", "https://host.foo.com/", nil)
+	setDefaultTime(input)
+	input.Header.Add("p", "phfft")
+
+	output, _ := http.NewRequest("POST", "https://host.foo.com/", nil)
+	output.Header = http.Header{
+		"Host":          []string{"host.foo.com"},
+		"Date":          []string{"Mon, 09 Sep 2011 23:36:00 GMT"},
+		"Authorization": []string{"AWS4-HMAC-SHA256 Credential=AKIDEXAMPLE/20110909/us-east-1/host/aws4_request, SignedHeaders=date;host;p, Signature=debf546796015d6f6ded8626f5ce98597c33b47b9164cf6b17b4642036fcb592"},
+		"P":             []string{"phfft"},
+	}
+
+	oldNow := now
+	defer func() { now = oldNow }()
+	now = setTime(defaultTime)
+
+	testRequestSigner(t, defaultRequestSigner, input, output)
+}
+
+func TestAwsV4Signature_PostRequestWithBody(t *testing.T) {
+	input, _ := http.NewRequest("POST", "https://host.foo.com/", strings.NewReader("foo=bar"))
+	setDefaultTime(input)
+	input.Header.Add("Content-Type", "application/x-www-form-urlencoded")
+
+	output, _ := http.NewRequest("POST", "https://host.foo.com/", nil)
+	output.Header = http.Header{
+		"Host":          []string{"host.foo.com"},
+		"Date":          []string{"Mon, 09 Sep 2011 23:36:00 GMT"},
+		"Content-Type":  []string{"application/x-www-form-urlencoded"},
+		"Authorization": []string{"AWS4-HMAC-SHA256 Credential=AKIDEXAMPLE/20110909/us-east-1/host/aws4_request, SignedHeaders=content-type;date;host, Signature=5a15b22cf462f047318703b92e6f4f38884e4a7ab7b1d6426ca46a8bd1c26cbc"},
+	}
+
+	oldNow := now
+	defer func() { now = oldNow }()
+	now = setTime(defaultTime)
+
+	testRequestSigner(t, defaultRequestSigner, input, output)
+}
+
+func TestAwsV4Signature_PostRequestWithQueryString(t *testing.T) {
+	input, _ := http.NewRequest("POST", "https://host.foo.com/?foo=bar", nil)
+	setDefaultTime(input)
+
+	output, _ := http.NewRequest("POST", "https://host.foo.com/?foo=bar", nil)
+	output.Header = http.Header{
+		"Host":          []string{"host.foo.com"},
+		"Date":          []string{"Mon, 09 Sep 2011 23:36:00 GMT"},
+		"Authorization": []string{"AWS4-HMAC-SHA256 Credential=AKIDEXAMPLE/20110909/us-east-1/host/aws4_request, SignedHeaders=date;host, Signature=b6e3b79003ce0743a491606ba1035a804593b0efb1e20a11cba83f8c25a57a92"},
+	}
+
+	oldNow := now
+	defer func() { now = oldNow }()
+	now = setTime(defaultTime)
+
+	testRequestSigner(t, defaultRequestSigner, input, output)
+}
+
+func TestAwsV4Signature_GetRequestWithSecurityToken(t *testing.T) {
+	input, _ := http.NewRequest("GET", "https://ec2.us-east-2.amazonaws.com?Action=DescribeRegions&Version=2013-10-15", nil)
+
+	output, _ := http.NewRequest("GET", "https://ec2.us-east-2.amazonaws.com?Action=DescribeRegions&Version=2013-10-15", nil)
+	output.Header = http.Header{
+		"Host":                 []string{"ec2.us-east-2.amazonaws.com"},
+		"Authorization":        []string{"AWS4-HMAC-SHA256 Credential=" + accessKeyId + "/20200811/us-east-2/ec2/aws4_request, SignedHeaders=host;x-amz-date;x-amz-security-token, Signature=631ea80cddfaa545fdadb120dc92c9f18166e38a5c47b50fab9fce476e022855"},
+		"X-Amz-Date":           []string{"20200811T065522Z"},
+		"X-Amz-Security-Token": []string{securityToken},
+	}
+
+	oldNow := now
+	defer func() { now = oldNow }()
+	now = setTime(secondDefaultTime)
+
+	testRequestSigner(t, requestSignerWithToken, input, output)
+}
+
+func TestAwsV4Signature_PostRequestWithSecurityToken(t *testing.T) {
+	input, _ := http.NewRequest("POST", "https://sts.us-east-2.amazonaws.com?Action=GetCallerIdentity&Version=2011-06-15", nil)
+
+	output, _ := http.NewRequest("POST", "https://sts.us-east-2.amazonaws.com?Action=GetCallerIdentity&Version=2011-06-15", nil)
+	output.Header = http.Header{
+		"Authorization":        []string{"AWS4-HMAC-SHA256 Credential=" + accessKeyId + "/20200811/us-east-2/sts/aws4_request, SignedHeaders=host;x-amz-date;x-amz-security-token, Signature=73452984e4a880ffdc5c392355733ec3f5ba310d5e0609a89244440cadfe7a7a"},
+		"Host":                 []string{"sts.us-east-2.amazonaws.com"},
+		"X-Amz-Date":           []string{"20200811T065522Z"},
+		"X-Amz-Security-Token": []string{securityToken},
+	}
+
+	oldNow := now
+	defer func() { now = oldNow }()
+	now = setTime(secondDefaultTime)
+
+	testRequestSigner(t, requestSignerWithToken, input, output)
+}
+
+func TestAwsV4Signature_PostRequestWithSecurityTokenAndAdditionalHeaders(t *testing.T) {
+	requestParams := "{\"KeySchema\":[{\"KeyType\":\"HASH\",\"AttributeName\":\"Id\"}],\"TableName\":\"TestTable\",\"AttributeDefinitions\":[{\"AttributeName\":\"Id\",\"AttributeType\":\"S\"}],\"ProvisionedThroughput\":{\"WriteCapacityUnits\":5,\"ReadCapacityUnits\":5}}"
+	input, _ := http.NewRequest("POST", "https://dynamodb.us-east-2.amazonaws.com/", strings.NewReader(requestParams))
+	input.Header.Add("Content-Type", "application/x-amz-json-1.0")
+	input.Header.Add("x-amz-target", "DynamoDB_20120810.CreateTable")
+
+	output, _ := http.NewRequest("POST", "https://dynamodb.us-east-2.amazonaws.com/", strings.NewReader(requestParams))
+	output.Header = http.Header{
+		"Authorization":        []string{"AWS4-HMAC-SHA256 Credential=" + accessKeyId + "/20200811/us-east-2/dynamodb/aws4_request, SignedHeaders=content-type;host;x-amz-date;x-amz-security-token;x-amz-target, Signature=fdaa5b9cc9c86b80fe61eaf504141c0b3523780349120f2bd8145448456e0385"},
+		"Host":                 []string{"dynamodb.us-east-2.amazonaws.com"},
+		"X-Amz-Date":           []string{"20200811T065522Z"},
+		"Content-Type":         []string{"application/x-amz-json-1.0"},
+		"X-Amz-Target":         []string{"DynamoDB_20120810.CreateTable"},
+		"X-Amz-Security-Token": []string{securityToken},
+	}
+
+	oldNow := now
+	defer func() { now = oldNow }()
+	now = setTime(secondDefaultTime)
+
+	testRequestSigner(t, requestSignerWithToken, input, output)
+}
+
+func TestAwsV4Signature_PostRequestWithAmzDateButNoSecurityToken(t *testing.T) {
+	var requestSigner = &awsRequestSigner{
+		RegionName: "us-east-2",
+		AwsSecurityCredentials: map[string]string{
+			"access_key_id":     accessKeyId,
+			"secret_access_key": secretAccessKey,
+		},
+	}
+
+	input, _ := http.NewRequest("POST", "https://sts.us-east-2.amazonaws.com?Action=GetCallerIdentity&Version=2011-06-15", nil)
+
+	output, _ := http.NewRequest("POST", "https://sts.us-east-2.amazonaws.com?Action=GetCallerIdentity&Version=2011-06-15", nil)
+	output.Header = http.Header{
+		"Authorization": []string{"AWS4-HMAC-SHA256 Credential=" + accessKeyId + "/20200811/us-east-2/sts/aws4_request, SignedHeaders=host;x-amz-date, Signature=d095ba304919cd0d5570ba8a3787884ee78b860f268ed040ba23831d55536d56"},
+		"Host":          []string{"sts.us-east-2.amazonaws.com"},
+		"X-Amz-Date":    []string{"20200811T065522Z"},
+	}
+
+	oldNow := now
+	defer func() { now = oldNow }()
+	now = setTime(secondDefaultTime)
+
+	testRequestSigner(t, requestSigner, input, output)
+}