feat(storage): GenerateSignedPostPolicyV4 can use existing creds to authenticate

storage/bucket.go

@@ -282,8 +282,54 @@ func (b *BucketHandle) SignedURL(object string, opts *SignedURLOptions) (string,
 	return SignedURL(b.name, object, newopts)
 }
 
-// TODO: Add a similar wrapper for GenerateSignedPostPolicyV4 allowing users to
-// omit PrivateKey/SignBytes
+// GenerateSignedPostPolicyV4 generates a PostPolicyV4 value from bucket, object and opts.
+// The generated URL and fields will then allow an unauthenticated client to perform multipart uploads.
+//
+// This method only requires the Expires field in the specified PostPolicyV4Options
+// to be non-nil. If not provided, it attempts to fill the GoogleAccessID and PrivateKey
+// from the GOOGLE_APPLICATION_CREDENTIALS environment variable.
+// If you are authenticating with a custom HTTP client, Service Account based
+// auto-detection will be hindered.
+//
+// If no private key is found, it attempts to use the GoogleAccessID to sign the URL.
+// This requires the IAM Service Account Credentials API to be enabled
+// (https://console.developers.google.com/apis/api/iamcredentials.googleapis.com/overview)
+// and iam.serviceAccounts.signBlob permissions on the GoogleAccessID service account.
+// If you do not want these fields set for you, you may pass them in through opts or use
+// GenerateSignedPostPolicyV4(bucket, name string, opts *PostPolicyV4Options) instead.
+func (b *BucketHandle) GenerateSignedPostPolicyV4(object string, opts *PostPolicyV4Options) (*PostPolicyV4, error) {
+	if opts.GoogleAccessID != "" && (opts.SignRawBytes != nil || opts.SignBytes != nil || len(opts.PrivateKey) > 0) {
+		return GenerateSignedPostPolicyV4(b.name, object, opts)
+	}
+	// Make a copy of opts so we don't modify the pointer parameter.
+	newopts := opts.clone()
+
+	if newopts.GoogleAccessID == "" {
+		id, err := b.detectDefaultGoogleAccessID()
+		if err != nil {
+			return nil, err
+		}
+		newopts.GoogleAccessID = id
+	}
+	if newopts.SignBytes == nil && newopts.SignRawBytes == nil && len(newopts.PrivateKey) == 0 {
+		if b.c.creds != nil && len(b.c.creds.JSON) > 0 {
+			var sa struct {
+				PrivateKey string `json:"private_key"`
+			}
+			err := json.Unmarshal(b.c.creds.JSON, &sa)
+			if err == nil && sa.PrivateKey != "" {
+				newopts.PrivateKey = []byte(sa.PrivateKey)
+			}
+		}
+
+		// Don't error out if we can't unmarshal the private key from the client,
+		// fallback to the default sign function for the service account.
+		if len(newopts.PrivateKey) == 0 {
+			newopts.SignRawBytes = b.defaultSignBytesFunc(newopts.GoogleAccessID)
+		}
+	}
+	return GenerateSignedPostPolicyV4(b.name, object, newopts)
+}
 
 func (b *BucketHandle) detectDefaultGoogleAccessID() (string, error) {
 	returnErr := errors.New("no credentials found on client and not on GCE (Google Compute Engine)")

storage/integration_test.go

@@ -4174,7 +4174,7 @@ func TestIntegration_PostPolicyV4(t *testing.T) {
 	object := b.Object(objectName)
 	defer h.mustDeleteObject(object)
 
-	pv4, err := GenerateSignedPostPolicyV4(newBucketName, objectName, opts)
+	pv4, err := b.GenerateSignedPostPolicyV4(objectName, opts)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -4280,6 +4280,78 @@ func TestIntegration_SignedURL_Bucket(t *testing.T) {
 	}
 }
 
+func TestIntegration_PostPolicyV4_Bucket(t *testing.T) {
+	h := testHelper{t}
+	ctx := context.Background()
+
+	if testing.Short() && !replaying {
+		t.Skip("Integration tests skipped in short mode")
+	}
+
+	// We explictly send the key to the client to sign with the private key
+	clientWithCredentials := newTestClientWithExplicitCredentials(ctx, t)
+	defer clientWithCredentials.Close()
+
+	// Create another client to test the sign byte function as well
+	clientWithoutPrivateKey := testConfig(ctx, t, ScopeFullControl, "https://www.googleapis.com/auth/cloud-platform")
+	defer clientWithoutPrivateKey.Close()
+
+	jwt, err := testutil.JWTConfig()
+	if err != nil {
+		t.Fatalf("unable to find test credentials: %v", err)
+	}
+
+	statusCodeToRespond := 200
+
+	for _, test := range []struct {
+		desc   string
+		opts   PostPolicyV4Options
+		client *Client
+	}{
+		{
+			desc: "signing with the private key",
+			opts: PostPolicyV4Options{
+				Expires: time.Now().Add(30 * time.Minute),
+
+				Fields: &PolicyV4Fields{
+					StatusCodeOnSuccess: statusCodeToRespond,
+					ContentType:         "text/plain",
+					ACL:                 "public-read",
+				},
+			},
+			client: clientWithCredentials,
+		},
+		{
+			desc: "signing with the default sign bytes func",
+			opts: PostPolicyV4Options{
+				Expires:        time.Now().Add(30 * time.Minute),
+				GoogleAccessID: jwt.Email,
+				Fields: &PolicyV4Fields{
+					StatusCodeOnSuccess: statusCodeToRespond,
+					ContentType:         "text/plain",
+					ACL:                 "public-read",
+				},
+			},
+			client: clientWithoutPrivateKey,
+		},
+	} {
+		t.Run(test.desc, func(t *testing.T) {
+			objectName := uidSpace.New()
+			object := test.client.Bucket(bucketName).Object(objectName)
+			defer h.mustDeleteObject(object)
+
+			pv4, err := test.client.Bucket(bucketName).GenerateSignedPostPolicyV4(objectName, &test.opts)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			if err := verifyPostPolicy(pv4, object, bytes.Repeat([]byte("a"), 25), statusCodeToRespond); err != nil {
+				t.Fatal(err)
+			}
+		})
+	}
+}
+
 // Tests that the same SignBytes function works for both
 // SignRawBytes on GeneratePostPolicyV4 and SignBytes on SignedURL
 func TestIntegration_PostPolicyV4_SignedURL_WithSignBytes(t *testing.T) {
@@ -4295,7 +4367,7 @@ func TestIntegration_PostPolicyV4_SignedURL_WithSignBytes(t *testing.T) {
 	h := testHelper{t}
 	projectID := testutil.ProjID()
 	bucketName := uidSpace.New()
-	objectName := "my-object.txt"
+	objectName := uidSpace.New()
 	fileBody := bytes.Repeat([]byte("b"), 25)
 	bucket := client.Bucket(bucketName)
 
@@ -4335,7 +4407,7 @@ func TestIntegration_PostPolicyV4_SignedURL_WithSignBytes(t *testing.T) {
 		},
 	}
 
-	pv4, err := GenerateSignedPostPolicyV4(bucketName, objectName, ppv4Opts)
+	pv4, err := bucket.GenerateSignedPostPolicyV4(objectName, ppv4Opts)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -4523,7 +4595,7 @@ func (h testHelper) mustObjectAttrs(o *ObjectHandle) *ObjectAttrs {
 
 func (h testHelper) mustDeleteObject(o *ObjectHandle) {
 	if err := o.Delete(context.Background()); err != nil {
-		h.t.Fatalf("%s: object delete: %v", loc(), err)
+		h.t.Fatalf("%s: delete object %s from bucket %s: %v", loc(), o.ObjectName(), o.BucketName(), err)
 	}
 }
 

storage/post_policy_v4.go

@@ -116,6 +116,20 @@ type PostPolicyV4Options struct {
 	shouldHashSignBytes bool
 }
 
+func (opts *PostPolicyV4Options) clone() *PostPolicyV4Options {
+	return &PostPolicyV4Options{
+		GoogleAccessID:      opts.GoogleAccessID,
+		PrivateKey:          opts.PrivateKey,
+		SignBytes:           opts.SignBytes,
+		Expires:             opts.Expires,
+		Style:               opts.Style,
+		Insecure:            opts.Insecure,
+		Fields:              opts.Fields,
+		Conditions:          opts.Conditions,
+		shouldHashSignBytes: opts.shouldHashSignBytes,
+	}
+}
+
 // PolicyV4Fields describes the attributes for a PostPolicyV4 request.
 type PolicyV4Fields struct {
 	// ACL specifies the access control permissions for the object.