authhandler: Rename to CmdAuthorizationHandler and add example_test.go

authhandler/cmd_authhandler.go

@@ -0,0 +1,30 @@
+// 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 authhandler
+
+import (
+	"fmt"
+)
+
+// CmdAuthorizationHandler returns a command line auth handler
+// that prints the auth URL on the console and prompts the user to
+// authorize in the browser and paste the auth code back via stdin.
+//
+// Per OAuth protocol, a unique "state" string should be sent and verified
+// before exchanging auth code for OAuth token to prevent CSRF attacks.
+//
+// For convenience, this handler returns a pre-configured state
+// instead of asking the user to additionally paste the state from
+// the auth response. In order for this to work, the state
+// configured here must match the state used in authCodeURL.
+func CmdAuthorizationHandler(state string) AuthorizationHandler {
+	return func(authCodeURL string) (string, string, error) {
+		fmt.Printf("Go to the following link in your browser:\n\n   %s\n\n", authCodeURL)
+		fmt.Println("Enter authorization code:")
+		var code string
+		fmt.Scanln(&code)
+		return code, state, nil
+	}
+}