fix(auth): enable self-signed JWT for non-GDU universe domain (#10831)

* default to UseSelfSignedJWT=true for non-GDU service account flows
* add error for UseSelfSignedJWT without aud or scope

auth/credentials/detect_test.go

@@ -459,11 +459,10 @@ func TestDefaultCredentials_ServiceAccountKeySelfSigned_UniverseDomain(t *testin
 	now = func() time.Time { return time.Date(2000, 2, 1, 12, 30, 0, 0, time.UTC) }
 	defer func() { now = oldNow }()
 	wantTok := "eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCIsImtpZCI6ImFiY2RlZjEyMzQ1Njc4OTAifQ.eyJpc3MiOiJnb3BoZXJAZmFrZV9wcm9qZWN0LmlhbS5nc2VydmljZWFjY291bnQuY29tIiwic2NvcGUiOiJodHRwczovL3d3dy5nb29nbGVhcGlzLmNvbS9hdXRoL2Nsb3VkLXBsYXRmb3JtIiwiZXhwIjo5NDk0MTE4MDAsImlhdCI6OTQ5NDA4MjAwLCJhdWQiOiIiLCJzdWIiOiJnb3BoZXJAZmFrZV9wcm9qZWN0LmlhbS5nc2VydmljZWFjY291bnQuY29tIn0.n9Hggd-1Vw4WTQiWkh7q9r5eDsz-khU5vwkZl2VmgdUF3ZxDq1ARzchCNtTifeorzbp9C0i0vCr855G7FZkVCJXPVMcnxbwfMSafUYmVsmutbQiV9eTWfWM0_Ljiwa9GEbv1bN06Lz4LrelPKEaxsDbY6tU8LJUiome_gSMLfLk"
-
 	creds, err := DetectDefault(&DetectOptions{
-		CredentialsJSON:  b,
-		Scopes:           []string{"https://www.googleapis.com/auth/cloud-platform"},
-		UseSelfSignedJWT: true,
+		// default scopes are set in resolveDetectOptions before calling DetectDefault.
+		Scopes:          []string{"https://www.googleapis.com/auth/cloud-platform"},
+		CredentialsJSON: b,
 	})
 	if err != nil {
 		t.Fatal(err)
@@ -805,26 +804,29 @@ func TestDefaultCredentials_UniverseDomain(t *testing.T) {
 		{
 			name: "service account json with file universe domain",
 			opts: &DetectOptions{
-				CredentialsFile:  "../internal/testdata/sa_universe_domain.json",
-				UseSelfSignedJWT: true,
+				CredentialsFile: "../internal/testdata/sa_universe_domain.json",
+				// default scopes are set in resolveDetectOptions before calling DetectDefault.
+				Scopes: []string{"https://www.googleapis.com/auth/cloud-platform"},
 			},
 			want: "example.com",
 		},
 		{
 			name: "service account json with options universe domain",
 			opts: &DetectOptions{
-				CredentialsFile:  "../internal/testdata/sa.json",
-				UseSelfSignedJWT: true,
-				UniverseDomain:   "foo.com",
+				CredentialsFile: "../internal/testdata/sa.json",
+				// default scopes are set in resolveDetectOptions before calling DetectDefault.
+				Scopes:         []string{"https://www.googleapis.com/auth/cloud-platform"},
+				UniverseDomain: "foo.com",
 			},
 			want: "foo.com",
 		},
 		{
 			name: "service account json with file and options universe domain",
 			opts: &DetectOptions{
-				CredentialsFile:  "../internal/testdata/sa_universe_domain.json",
-				UseSelfSignedJWT: true,
-				UniverseDomain:   "foo.com",
+				CredentialsFile: "../internal/testdata/sa_universe_domain.json",
+				// default scopes are set in resolveDetectOptions before calling DetectDefault.
+				Scopes:         []string{"https://www.googleapis.com/auth/cloud-platform"},
+				UniverseDomain: "foo.com",
 			},
 			want: "foo.com",
 		},
@@ -923,8 +925,9 @@ func TestDefaultCredentials_UniverseDomain(t *testing.T) {
 		{
 			name: "impersonated service account json",
 			opts: &DetectOptions{
-				CredentialsFile:  "../internal/testdata/imp.json",
-				UseSelfSignedJWT: true,
+				CredentialsFile: "../internal/testdata/imp.json",
+				// default scopes are set in resolveDetectOptions before calling DetectDefault.
+				Scopes: []string{"https://www.googleapis.com/auth/cloud-platform"},
 			},
 			want: "googleapis.com",
 		},
@@ -938,17 +941,20 @@ func TestDefaultCredentials_UniverseDomain(t *testing.T) {
 		{
 			name: "impersonated service account json with options universe domain",
 			opts: &DetectOptions{
-				CredentialsFile:  "../internal/testdata/imp.json",
-				UseSelfSignedJWT: true,
-				UniverseDomain:   "foo.com",
+				CredentialsFile: "../internal/testdata/imp.json",
+				// default scopes are set in resolveDetectOptions before calling DetectDefault.
+				Scopes:         []string{"https://www.googleapis.com/auth/cloud-platform"},
+				UniverseDomain: "foo.com",
 			},
 			want: "foo.com",
 		},
 		{
 			name: "impersonated service account json with file and options universe domain",
 			opts: &DetectOptions{
 				CredentialsFile: "../internal/testdata/imp_universe_domain.json",
-				UniverseDomain:  "foo.com",
+				// default scopes are set in resolveDetectOptions before calling DetectDefault.
+				Scopes:         []string{"https://www.googleapis.com/auth/cloud-platform"},
+				UniverseDomain: "foo.com",
 			},
 			want: "foo.com",
 		},

auth/credentials/filetypes.go

@@ -124,8 +124,14 @@ func resolveUniverseDomain(optsUniverseDomain, fileUniverseDomain string) string
 }
 
 func handleServiceAccount(f *credsfile.ServiceAccountFile, opts *DetectOptions) (auth.TokenProvider, error) {
+	ud := resolveUniverseDomain(opts.UniverseDomain, f.UniverseDomain)
 	if opts.UseSelfSignedJWT {
 		return configureSelfSignedJWT(f, opts)
+	} else if ud != "" && ud != internalauth.DefaultUniverseDomain {
+		// For non-GDU universe domains, token exchange is impossible and services
+		// must support self-signed JWTs.
+		opts.UseSelfSignedJWT = true
+		return configureSelfSignedJWT(f, opts)
 	}
 	opts2LO := &auth.Options2LO{
 		Email:        f.ClientEmail,

auth/credentials/selfsignedjwt.go

@@ -17,6 +17,7 @@ package credentials
 import (
 	"context"
 	"crypto/rsa"
+	"errors"
 	"fmt"
 	"strings"
 	"time"
@@ -35,6 +36,9 @@ var (
 // configureSelfSignedJWT uses the private key in the service account to create
 // a JWT without making a network call.
 func configureSelfSignedJWT(f *credsfile.ServiceAccountFile, opts *DetectOptions) (auth.TokenProvider, error) {
+	if len(opts.scopes()) == 0 && opts.Audience == "" {
+		return nil, errors.New("credentials: both scopes and audience are empty")
+	}
 	pk, err := internal.ParseKey([]byte(f.PrivateKey))
 	if err != nil {
 		return nil, fmt.Errorf("credentials: could not parse key: %w", err)

auth/credentials/selfsignedjwt_test.go

@@ -40,7 +40,7 @@ var jwtJSONKey = []byte(`{
 	"audience": "https://testpervice.googleapis.com/"
   }`)
 
-func TestDefaultCredentials_SelfSignedJSON(t *testing.T) {
+func TestDetectDefault_SelfSignedJSON(t *testing.T) {
 	privateKey, jsonKey, err := setupFakeKey()
 	if err != nil {
 		t.Fatal(err)
@@ -51,7 +51,7 @@ func TestDefaultCredentials_SelfSignedJSON(t *testing.T) {
 		UseSelfSignedJWT: true,
 	})
 	if err != nil {
-		t.Fatalf("DefaultCredentials(%s): %v", jsonKey, err)
+		t.Fatalf("DetectDefault(%s): %v", jsonKey, err)
 	}
 
 	tok, err := tp.Token(context.Background())
@@ -102,7 +102,7 @@ func TestDefaultCredentials_SelfSignedJSON(t *testing.T) {
 	}
 }
 
-func TestDefaultCredentials_SelfSignedWithScope(t *testing.T) {
+func TestDetectDefault_SelfSignedWithScope(t *testing.T) {
 	privateKey, jsonKey, err := setupFakeKey()
 	if err != nil {
 		t.Fatal(err)
@@ -113,7 +113,7 @@ func TestDefaultCredentials_SelfSignedWithScope(t *testing.T) {
 		UseSelfSignedJWT: true,
 	})
 	if err != nil {
-		t.Fatalf("DefaultCredentials(%s): %v", jsonKey, err)
+		t.Fatalf("DetectDefault(%s): %v", jsonKey, err)
 	}
 
 	tok, err := tp.Token(context.Background())
@@ -164,6 +164,42 @@ func TestDefaultCredentials_SelfSignedWithScope(t *testing.T) {
 	}
 }
 
+func TestDetectDefault_SelfSignedWithAudienceAndScope(t *testing.T) {
+	_, jsonKey, err := setupFakeKey()
+	if err != nil {
+		t.Fatal(err)
+	}
+	_, err = DetectDefault(&DetectOptions{
+		CredentialsJSON:  jsonKey,
+		Audience:         "audience",
+		Scopes:           []string{"scope1", "scope2"},
+		UseSelfSignedJWT: true,
+	})
+	if err == nil {
+		t.Fatal("DetectDefault(): want non-nil err")
+	}
+	if want := "credentials: both scopes and audience were provided"; err.Error() != want {
+		t.Errorf("TokenType = %q, want %q", err, want)
+	}
+}
+
+func TestDetectDefault_SelfSignedWithoutAudienceOrScope(t *testing.T) {
+	_, jsonKey, err := setupFakeKey()
+	if err != nil {
+		t.Fatal(err)
+	}
+	_, err = DetectDefault(&DetectOptions{
+		CredentialsJSON:  jsonKey,
+		UseSelfSignedJWT: true,
+	})
+	if err == nil {
+		t.Fatal("DetectDefault(): want non-nil err")
+	}
+	if want := "credentials: both scopes and audience are empty"; err.Error() != want {
+		t.Errorf("DetectDefault = %q, want %q", err, want)
+	}
+}
+
 // setupFakeKey generates a key we can use in the test data.
 func setupFakeKey() (*rsa.PrivateKey, []byte, error) {
 	// Generate a key we can use in the test data.

auth/internal/testdata/imp_universe_domain.json

@@ -8,7 +8,7 @@
         "type": "service_account",
         "project_id": "fake_project",
         "private_key_id": "89asd789789uo473454c47543",
-        "private_key": "fake",
+        "private_key": "-----BEGIN PRIVATE KEY-----\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\n-----END PRIVATE KEY-----\n",
         "client_email": "sa@fake_project.iam.gserviceaccount.com",
         "client_id": "gopher",
         "auth_uri": "https://accounts.google.com/o/oauth2/auth",