diff --git a/google/google.go b/google/google.go
index e247491..2c8f1bd 100644
--- a/google/google.go
+++ b/google/google.go
@@ -115,14 +115,13 @@
 	RefreshToken string `json:"refresh_token"`
 
 	// External Account fields
-	Audience string `json:"audience"`
-	SubjectTokenType string `json:"subject_token_type"`
-	TokenURLExternal string `json:"token_url"`
-	TokenInfoURL string `json:"token_info_url"`
-	ServiceAccountImpersonationURL string `json:"service_account_impersonation_url"`
-	CredentialSource externalaccount.CredentialSource `json:"credential_source"`
-	QuotaProjectID string `json:"quota_project_id"`
-
+	Audience                       string                           `json:"audience"`
+	SubjectTokenType               string                           `json:"subject_token_type"`
+	TokenURLExternal               string                           `json:"token_url"`
+	TokenInfoURL                   string                           `json:"token_info_url"`
+	ServiceAccountImpersonationURL string                           `json:"service_account_impersonation_url"`
+	CredentialSource               externalaccount.CredentialSource `json:"credential_source"`
+	QuotaProjectID                 string                           `json:"quota_project_id"`
 }
 
 func (f *credentialsFile) jwtConfig(scopes []string) *jwt.Config {
@@ -155,16 +154,16 @@
 		return cfg.TokenSource(ctx, tok), nil
 	case externalAccountKey:
 		cfg := &externalaccount.Config{
-			Audience:	f.Audience,
-			SubjectTokenType: f.SubjectTokenType,
-			TokenURL: f.TokenURLExternal,
-			TokenInfoURL: f.TokenInfoURL,
+			Audience:                       f.Audience,
+			SubjectTokenType:               f.SubjectTokenType,
+			TokenURL:                       f.TokenURLExternal,
+			TokenInfoURL:                   f.TokenInfoURL,
 			ServiceAccountImpersonationURL: f.ServiceAccountImpersonationURL,
-			ClientSecret: f.ClientSecret,
-			ClientID: f.ClientID,
-			CredentialSource: f.CredentialSource,
-			QuotaProjectID: f.QuotaProjectID,
-			Scopes: scopes,
+			ClientSecret:                   f.ClientSecret,
+			ClientID:                       f.ClientID,
+			CredentialSource:               f.CredentialSource,
+			QuotaProjectID:                 f.QuotaProjectID,
+			Scopes:                         scopes,
 		}
 		return cfg.TokenSource(ctx), nil
 	case "":
diff --git a/google/internal/externalaccount/basecredentials.go b/google/internal/externalaccount/basecredentials.go
index 3291d46..dff0881 100644
--- a/google/internal/externalaccount/basecredentials.go
+++ b/google/internal/externalaccount/basecredentials.go
@@ -66,9 +66,11 @@
 }
 
 // parse determines the type of CredentialSource needed
-func (c *Config) parse() baseCredentialSource {
+func (c *Config) parse(ctx context.Context) baseCredentialSource {
 	if c.CredentialSource.File != "" {
 		return fileCredentialSource{File: c.CredentialSource.File, Format: c.CredentialSource.Format}
+	} else if c.CredentialSource.URL != "" {
+		return urlCredentialSource{URL: c.CredentialSource.URL, Format: c.CredentialSource.Format, ctx: ctx}
 	}
 	return nil
 }
@@ -87,7 +89,7 @@
 func (ts tokenSource) Token() (*oauth2.Token, error) {
 	conf := ts.conf
 
-	credSource := conf.parse()
+	credSource := conf.parse(ts.ctx)
 	if credSource == nil {
 		return nil, fmt.Errorf("oauth2/google: unable to parse credential source")
 	}
diff --git a/google/internal/externalaccount/filecredsource_test.go b/google/internal/externalaccount/filecredsource_test.go
index 0bc8048..56dd71e 100644
--- a/google/internal/externalaccount/filecredsource_test.go
+++ b/google/internal/externalaccount/filecredsource_test.go
@@ -5,6 +5,7 @@
 package externalaccount
 
 import (
+	"context"
 	"testing"
 )
 
@@ -55,7 +56,7 @@
 		tfc.CredentialSource = test.cs
 
 		t.Run(test.name, func(t *testing.T) {
-			out, err := tfc.parse().subjectToken()
+			out, err := tfc.parse(context.Background()).subjectToken()
 			if err != nil {
 				t.Errorf("Method subjectToken() errored.")
 			} else if test.want != out {
diff --git a/google/internal/externalaccount/urlcredsource.go b/google/internal/externalaccount/urlcredsource.go
new file mode 100644
index 0000000..b0d5d35
--- /dev/null
+++ b/google/internal/externalaccount/urlcredsource.go
@@ -0,0 +1,71 @@
+// Copyright 2020 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 (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"golang.org/x/oauth2"
+	"io"
+	"io/ioutil"
+	"net/http"
+)
+
+type urlCredentialSource struct {
+	URL     string
+	Headers map[string]string
+	Format  format
+	ctx     context.Context
+}
+
+func (cs urlCredentialSource) subjectToken() (string, error) {
+	client := oauth2.NewClient(cs.ctx, nil)
+	req, err := http.NewRequest("GET", cs.URL, nil)
+	if err != nil {
+		return "", fmt.Errorf("oauth2/google: HTTP request for URL-sourced credential failed: %v", err)
+	}
+	req = req.WithContext(cs.ctx)
+
+	for key, val := range cs.Headers {
+		req.Header.Add(key, val)
+	}
+	resp, err := client.Do(req)
+	if err != nil {
+		return "", fmt.Errorf("oauth2/google: invalid response when retrieving subject token: %v", err)
+	}
+	defer resp.Body.Close()
+
+	tokenBytes, 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)
+	}
+
+	switch cs.Format.Type {
+	case "json":
+		jsonData := make(map[string]interface{})
+		err = json.Unmarshal(tokenBytes, &jsonData)
+		if err != nil {
+			return "", fmt.Errorf("oauth2/google: failed to unmarshal subject token file: %v", err)
+		}
+		val, ok := jsonData[cs.Format.SubjectTokenFieldName]
+		if !ok {
+			return "", errors.New("oauth2/google: provided subject_token_field_name not found in credentials")
+		}
+		token, ok := val.(string)
+		if !ok {
+			return "", errors.New("oauth2/google: improperly formatted subject token")
+		}
+		return token, nil
+	case "text":
+		return string(tokenBytes), nil
+	case "":
+		return string(tokenBytes), 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
new file mode 100644
index 0000000..592610f
--- /dev/null
+++ b/google/internal/externalaccount/urlcredsource_test.go
@@ -0,0 +1,92 @@
+// Copyright 2020 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 (
+	"context"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+var myURLToken = "testTokenValue"
+
+func TestRetrieveURLSubjectToken_Text(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.Method != "GET" {
+			t.Errorf("Unexpected request method, %v is found", r.Method)
+		}
+		w.Write([]byte("testTokenValue"))
+	}))
+	cs := CredentialSource{
+		URL:    ts.URL,
+		Format: format{Type: fileTypeText},
+	}
+	tfc := testFileConfig
+	tfc.CredentialSource = cs
+
+	out, err := tfc.parse(context.Background()).subjectToken()
+	if err != nil {
+		t.Fatalf("retrieveSubjectToken() failed: %v", err)
+	}
+	if out != myURLToken {
+		t.Errorf("got %v but want %v", out, myURLToken)
+	}
+}
+
+// Checking that retrieveSubjectToken properly defaults to type text
+func TestRetrieveURLSubjectToken_Untyped(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.Method != "GET" {
+			t.Errorf("Unexpected request method, %v is found", r.Method)
+		}
+		w.Write([]byte("testTokenValue"))
+	}))
+	cs := CredentialSource{
+		URL: ts.URL,
+	}
+	tfc := testFileConfig
+	tfc.CredentialSource = cs
+
+	out, err := tfc.parse(context.Background()).subjectToken()
+	if err != nil {
+		t.Fatalf("Failed to retrieve URL subject token: %v", err)
+	}
+	if out != myURLToken {
+		t.Errorf("got %v but want %v", out, myURLToken)
+	}
+}
+
+func TestRetrieveURLSubjectToken_JSON(t *testing.T) {
+	type tokenResponse struct {
+		TestToken string `json:"SubjToken"`
+	}
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if got, want := r.Method, "GET"; got != want {
+			t.Errorf("got %v, but want %v", r.Method, want)
+		}
+		resp := tokenResponse{TestToken: "testTokenValue"}
+		jsonResp, err := json.Marshal(resp)
+		if err != nil {
+			t.Errorf("Failed to marshal values: %v", err)
+		}
+		w.Write(jsonResp)
+	}))
+	cs := CredentialSource{
+		URL:    ts.URL,
+		Format: format{Type: fileTypeJSON, SubjectTokenFieldName: "SubjToken"},
+	}
+	tfc := testFileConfig
+	tfc.CredentialSource = cs
+
+	out, err := tfc.parse(context.Background()).subjectToken()
+	if err != nil {
+		t.Fatalf("%v", err)
+	}
+	if out != myURLToken {
+		t.Errorf("got %v but want %v", out, myURLToken)
+	}
+}