google/externalaccount: moves externalaccount package out of internal and exports it

go/programmable-auth-design for context. Adds support for user defined
 supplier methods to return subject tokens and AWS security credentials.

Change-Id: I7bc41f8c5202ae933fce516632f5049bbeb3d378
GitHub-Last-Rev: ac519b242f8315df572f1b205b0670f139bfc6c3
GitHub-Pull-Request: golang/oauth2#690
Reviewed-on: https://go-review.googlesource.com/c/oauth2/+/550835
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Leo Siracusa <leosiracusa@google.com>
Reviewed-by: Chris Smith <chrisdsmith@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cody Oss <codyoss@google.com>

google/externalaccount/urlcredsource_test.go

@@ -0,0 +1,131 @@
+// 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)
+		}
+		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
+
+	base, err := tfc.parse(context.Background())
+	if err != nil {
+		t.Fatalf("parse() failed %v", err)
+	}
+
+	out, err := base.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
+
+	base, err := tfc.parse(context.Background())
+	if err != nil {
+		t.Fatalf("parse() failed %v", err)
+	}
+
+	out, err := base.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
+
+	base, err := tfc.parse(context.Background())
+	if err != nil {
+		t.Fatalf("parse() failed %v", err)
+	}
+
+	out, err := base.subjectToken()
+	if err != nil {
+		t.Fatalf("%v", err)
+	}
+	if out != myURLToken {
+		t.Errorf("got %v but want %v", out, myURLToken)
+	}
+}
+
+func TestURLCredential_CredentialSourceType(t *testing.T) {
+	cs := CredentialSource{
+		URL:    "http://example.com",
+		Format: Format{Type: fileTypeText},
+	}
+	tfc := testFileConfig
+	tfc.CredentialSource = &cs
+
+	base, err := tfc.parse(context.Background())
+	if err != nil {
+		t.Fatalf("parse() failed %v", err)
+	}
+
+	if got, want := base.credentialSourceType(), "url"; got != want {
+		t.Errorf("got %v but want %v", got, want)
+	}
+}