downscope: add new examples and update existing ones.

google/downscope/tokenconsumer_test.go

@@ -0,0 +1,44 @@
+package downscope_test
+
+import (
+	"golang.org/x/oauth2"
+)
+
+type localTokenSource struct {
+	requestedPerms []string
+	requestedObject string
+	brokerURL string
+}
+
+func (localTokenSource) Token() (*oauth2.Token, error){
+	var remoteToken oauth2.Token
+	// retrieve remoteToken, an oauth2.Token, from token broker
+	return &remoteToken, nil
+}
+
+
+func Example() {
+	// A token consumer should define their own tokenSource.  In the Token() method,
+	// it should send a query to a token broker requesting a downscoped token.
+	// The token broker holds the root credential that is used to generate the
+	// downscoped token.
+
+	thisTokenSource := localTokenSource{
+		requestedPerms: []string{"inRole:roles/storage.objectViewer"},
+		requestedObject: "//storage.googleapis.com/projects/_/buckets/foo",
+		brokerURL: "yourURL.com/internal/broker",
+	}
+
+	// Wrap the TokenSource in an oauth2.ReuseTokenSource to enable automatic refreshing
+	refreshableTS := oauth2.ReuseTokenSource(nil, thisTokenSource)
+
+
+	// You can now use the token source to access Google Cloud Storage resources as follows.
+
+	// storageClient, err := storage.NewClient(ctx, option.WithTokenSource(refreshableTS))
+	// bkt := storageClient.Bucket(bucketName)
+	// obj := bkt.Object(objectName)
+	// rc, err := obj.NewReader(ctx)
+	// defer rc.Close()
+	// data, err := ioutil.ReadAll(rc)
+}