downscope: add new examples and update existing ones.

google/downscope/tokenbroker_test.go

@@ -0,0 +1,56 @@
+// Copyright 2021 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 downscope_test
+
+import (
+	"context"
+	"fmt"
+	"golang.org/x/oauth2/google"
+
+	"golang.org/x/oauth2"
+	"golang.org/x/oauth2/google/downscope"
+)
+
+
+
+func ExampleNewTokenSource() {
+	// This shows how to generate a downscoped token.  This code would be run on the
+	// token broker, which holds the root token used to generate the downscoped token.
+	ctx := context.Background()
+	// Initializes an accessBoundary with one Rule.
+	accessBoundary := []downscope.AccessBoundaryRule{
+		{
+			AvailableResource:    "//storage.googleapis.com/projects/_/buckets/foo",
+			AvailablePermissions: []string{"inRole:roles/storage.objectViewer"},
+		},
+	}
+
+	var rootSource oauth2.TokenSource
+	// This Source can be initialized in multiple ways; the following example uses
+	// Application Default Credentials.
+
+	rootSource, err := google.DefaultTokenSource(ctx, "https://www.googleapis.com/auth/cloud-platform")
+
+	dts, err := downscope.NewTokenSource(ctx, downscope.DownscopingConfig{RootSource: rootSource, Rules: accessBoundary})
+	if err != nil {
+		fmt.Printf("failed to generate downscoped token source: %v", err)
+		return
+	}
+
+	tok, err := dts.Token()
+	if err != nil {
+		fmt.Printf("failed to generate token: %v", err)
+		return
+	}
+	_ = tok
+	// You can now pass tok to a token consumer however you wish, such as exposing
+	// a REST API and sending it over HTTP.
+
+	// You can instead use the token held in myTokenSource to make
+	// Google Cloud Storage calls, as follows:
+
+	// storageClient, err := storage.NewClient(ctx, option.WithTokenSource(myTokenSource))
+
+}