diff --git a/google/internal/externalaccount/basecredentials.go b/google/internal/externalaccount/basecredentials.go
index 57a5870..2eb5c8e 100644
--- a/google/internal/externalaccount/basecredentials.go
+++ b/google/internal/externalaccount/basecredentials.go
@@ -96,7 +96,7 @@ func (c *Config) parse(ctx context.Context) (baseCredentialSource, error) {
 	} else if c.CredentialSource.File != "" {
 		return fileCredentialSource{File: c.CredentialSource.File, Format: c.CredentialSource.Format}, nil
 	} else if c.CredentialSource.URL != "" {
-		return urlCredentialSource{URL: c.CredentialSource.URL, Format: c.CredentialSource.Format, ctx: ctx}, nil
+		return urlCredentialSource{URL: c.CredentialSource.URL, Headers: c.CredentialSource.Headers, Format: c.CredentialSource.Format, ctx: ctx}, nil
 	}
 	return nil, fmt.Errorf("oauth2/google: unable to parse credential source")
 }
diff --git a/google/internal/externalaccount/sts_exchange.go b/google/internal/externalaccount/sts_exchange.go
index 1a1c9b4..fbb477d 100644
--- a/google/internal/externalaccount/sts_exchange.go
+++ b/google/internal/externalaccount/sts_exchange.go
@@ -9,6 +9,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
+	"io/ioutil"
 	"net/http"
 	"net/url"
 	"strconv"
@@ -63,9 +64,12 @@ func ExchangeToken(ctx context.Context, endpoint string, request *STSTokenExchan
 	}
 	defer resp.Body.Close()
 
-	bodyJson := json.NewDecoder(io.LimitReader(resp.Body, 1<<20))
+	body, err := ioutil.ReadAll(io.LimitReader(resp.Body, 1<<20))
+	if c := resp.StatusCode; c < 200 || c > 299 {
+		return nil, fmt.Errorf("oauth2/google: status code %d: %s", c, body)
+	}
 	var stsResp STSTokenExchangeResponse
-	err = bodyJson.Decode(&stsResp)
+	err = json.Unmarshal(body, &stsResp)
 	if err != nil {
 		return nil, fmt.Errorf("oauth2/google: failed to unmarshal response body from Secure Token Server: %v", err)
 
diff --git a/google/internal/externalaccount/urlcredsource.go b/google/internal/externalaccount/urlcredsource.go
index b0d5d35..91b8f20 100644
--- a/google/internal/externalaccount/urlcredsource.go
+++ b/google/internal/externalaccount/urlcredsource.go
@@ -39,15 +39,18 @@ func (cs urlCredentialSource) subjectToken() (string, error) {
 	}
 	defer resp.Body.Close()
 
-	tokenBytes, err := ioutil.ReadAll(io.LimitReader(resp.Body, 1<<20))
+	respBody, err := ioutil.ReadAll(io.LimitReader(resp.Body, 1<<20))
 	if err != nil {
 		return "", fmt.Errorf("oauth2/google: invalid body in subject token URL query: %v", err)
 	}
+	if c := resp.StatusCode; c < 200 || c > 299 {
+		return "", fmt.Errorf("oauth2/google: status code %d: %s", c, respBody)
+	}
 
 	switch cs.Format.Type {
 	case "json":
 		jsonData := make(map[string]interface{})
-		err = json.Unmarshal(tokenBytes, &jsonData)
+		err = json.Unmarshal(respBody, &jsonData)
 		if err != nil {
 			return "", fmt.Errorf("oauth2/google: failed to unmarshal subject token file: %v", err)
 		}
@@ -61,9 +64,9 @@ func (cs urlCredentialSource) subjectToken() (string, error) {
 		}
 		return token, nil
 	case "text":
-		return string(tokenBytes), nil
+		return string(respBody), nil
 	case "":
-		return string(tokenBytes), nil
+		return string(respBody), nil
 	default:
 		return "", errors.New("oauth2/google: invalid credential_source file format type")
 	}
diff --git a/google/internal/externalaccount/urlcredsource_test.go b/google/internal/externalaccount/urlcredsource_test.go
index 1b78e68..6874f11 100644
--- a/google/internal/externalaccount/urlcredsource_test.go
+++ b/google/internal/externalaccount/urlcredsource_test.go
@@ -7,6 +7,7 @@ package externalaccount
 import (
 	"context"
 	"encoding/json"
+	"fmt"
 	"net/http"
 	"net/http/httptest"
 	"testing"
@@ -19,11 +20,18 @@ func TestRetrieveURLSubjectToken_Text(t *testing.T) {
 		if r.Method != "GET" {
 			t.Errorf("Unexpected request method, %v is found", r.Method)
 		}
+		fmt.Println(r.Header)
+		if r.Header.Get("Metadata") != "True" {
+			t.Errorf("Metadata header not properly included.")
+		}
 		w.Write([]byte("testTokenValue"))
 	}))
+	heads := make(map[string]string)
+	heads["Metadata"] = "True"
 	cs := CredentialSource{
 		URL:    ts.URL,
 		Format: format{Type: fileTypeText},
+		Headers: heads,
 	}
 	tfc := testFileConfig
 	tfc.CredentialSource = cs