fix: Skipping credential lookup in emulator mode (#459)

Author: hiranya911

auth/auth.go

@@ -25,6 +25,8 @@ import (
 	"time"
 
 	"firebase.google.com/go/v4/internal"
+	"golang.org/x/oauth2"
+	"google.golang.org/api/option"
 	"google.golang.org/api/transport"
 )
 
@@ -47,6 +49,10 @@ var reservedClaims = []string{
 	"exp", "firebase", "iat", "iss", "jti", "nbf", "nonce", "sub",
 }
 
+var emulatorToken = &oauth2.Token{
+	AccessToken: "owner",
+}
+
 // Client is the interface for the Firebase auth service.
 //
 // Client facilitates generating custom JWT tokens for Firebase clients, and verifying ID tokens issued
@@ -114,7 +120,15 @@ func NewClient(ctx context.Context, conf *internal.AuthConfig) (*Client, error)
 		return nil, err
 	}
 
-	transport, _, err := transport.NewHTTPClient(ctx, conf.Opts...)
+	var opts []option.ClientOption
+	if isEmulator {
+		ts := oauth2.StaticTokenSource(emulatorToken)
+		opts = append(opts, option.WithTokenSource(ts))
+	} else {
+		opts = append(opts, conf.Opts...)
+	}
+
+	transport, _, err := transport.NewHTTPClient(ctx, opts...)
 	if err != nil {
 		return nil, err
 	}

auth/auth_test.go

@@ -296,15 +296,11 @@ func TestNewClientEmulatorHostEnvVar(t *testing.T) {
 	os.Setenv(emulatorHostEnvVar, emulatorHost)
 	defer os.Unsetenv(emulatorHostEnvVar)
 
-	conf := &internal.AuthConfig{
-		Opts: []option.ClientOption{
-			option.WithoutAuthentication(),
-		},
-	}
-	client, err := NewClient(context.Background(), conf)
+	client, err := NewClient(context.Background(), &internal.AuthConfig{})
 	if err != nil {
 		t.Fatal(err)
 	}
+
 	baseClient := client.baseClient
 	if baseClient.userManagementEndpoint != idToolkitV1Endpoint {
 		t.Errorf("baseClient.userManagementEndpoint = %q; want = %q", baseClient.userManagementEndpoint, idToolkitV1Endpoint)
@@ -778,6 +774,7 @@ func TestEmulatorVerifyIDTokenUnreachableEmulator(t *testing.T) {
 		t.Fatal(err)
 	}
 	client.httpClient.Client.Transport = eConnRefusedTransport{}
+	client.httpClient.RetryConfig = nil
 	client.isEmulator = true
 
 	token := getEmulatedIDToken(nil)
@@ -1239,6 +1236,7 @@ func TestEmulatorVerifySessionCookieUnreachableEmulator(t *testing.T) {
 		t.Fatal(err)
 	}
 	client.httpClient.Client.Transport = eConnRefusedTransport{}
+	client.httpClient.RetryConfig = nil
 	client.isEmulator = true
 
 	token := getEmulatedSessionCookie(nil)