Backport lib/utils/prompt improvements to [v9] (#13822)

`prompt.ContextReader`, along with various parts of `lib/utils/prompt`, where
re-written in master so we can alleviate input swallowing issues.

For various reasons I didn't backport all changes to v9, but the less-eager
input-swallowing loop is now what stands between us and issue #13021.

This isn't a backport of a specific PR, but instead a port of the entire
`lib/utils/prompt` package, as the PRs that touch the package unfortunately do
more than we want to backport. The interfaces are still compatible and I did
test various `tsh login` and `tsh ssh` scenarios.

I've thrown in #13382 for good measure, as well.

Closes #13021.

* Backport lib/utils/prompt improvements
* Fix lib/client tests
* Restore terminal state on exit (#13382)

lib/client/api_login_test.go

@@ -103,7 +103,7 @@ func TestTeleportClient_Login_localMFALogin(t *testing.T) {
 		promptWebauthn func(ctx context.Context, origin string, assertion *wanlib.CredentialAssertion) (*proto.MFAAuthenticateResponse, error)
 	}{}
 	var loginMocksMU sync.RWMutex
-	*client.PromptOTP = func(ctx context.Context, out io.Writer, in *prompt.ContextReader, question string) (string, error) {
+	*client.PromptOTP = func(ctx context.Context, out io.Writer, in prompt.Reader, question string) (string, error) {
 		loginMocksMU.RLock()
 		defer loginMocksMU.RUnlock()
 		return loginMocks.promptOTP(ctx)

lib/utils/prompt/confirmation.go

@@ -26,13 +26,27 @@ import (
 	"github.com/gravitational/trace"
 )
 
+// Reader is the interface for prompt readers.
+type Reader interface {
+	// ReadContext reads from the underlying buffer, respecting context
+	// cancellation.
+	ReadContext(ctx context.Context) ([]byte, error)
+}
+
+// SecureReader is the interface for password readers.
+type SecureReader interface {
+	// ReadPassword reads from the underlying buffer, respecting context
+	// cancellation.
+	ReadPassword(ctx context.Context) ([]byte, error)
+}
+
 // Confirmation prompts the user for a yes/no confirmation for question.
 // The prompt is written to out and the answer is read from in.
 //
-// question should be a plain sentece without "[yes/no]"-type hints at the end.
+// question should be a plain sentence without "[yes/no]"-type hints at the end.
 //
 // ctx can be canceled to abort the prompt.
-func Confirmation(ctx context.Context, out io.Writer, in *ContextReader, question string) (bool, error) {
+func Confirmation(ctx context.Context, out io.Writer, in Reader, question string) (bool, error) {
 	fmt.Fprintf(out, "%s [y/N]: ", question)
 	answer, err := in.ReadContext(ctx)
 	if err != nil {
@@ -49,14 +63,14 @@ func Confirmation(ctx context.Context, out io.Writer, in *ContextReader, questio
 // PickOne prompts the user to pick one of the provided string options.
 // The prompt is written to out and the answer is read from in.
 //
-// question should be a plain sentece without the list of provided options.
+// question should be a plain sentence without the list of provided options.
 //
 // ctx can be canceled to abort the prompt.
-func PickOne(ctx context.Context, out io.Writer, in *ContextReader, question string, options []string) (string, error) {
+func PickOne(ctx context.Context, out io.Writer, in Reader, question string, options []string) (string, error) {
 	fmt.Fprintf(out, "%s [%s]: ", question, strings.Join(options, ", "))
 	answerOrig, err := in.ReadContext(ctx)
 	if err != nil {
-		return "", trace.WrapWithMessage(err, "failed reading prompt response")
+		return "", trace.Wrap(err, "failed reading prompt response")
 	}
 	answer := strings.ToLower(strings.TrimSpace(string(answerOrig)))
 	for _, opt := range options {
@@ -72,11 +86,25 @@ func PickOne(ctx context.Context, out io.Writer, in *ContextReader, question str
 // The prompt is written to out and the answer is read from in.
 //
 // ctx can be canceled to abort the prompt.
-func Input(ctx context.Context, out io.Writer, in *ContextReader, question string) (string, error) {
+func Input(ctx context.Context, out io.Writer, in Reader, question string) (string, error) {
 	fmt.Fprintf(out, "%s: ", question)
 	answer, err := in.ReadContext(ctx)
 	if err != nil {
-		return "", trace.WrapWithMessage(err, "failed reading prompt response")
+		return "", trace.Wrap(err, "failed reading prompt response")
 	}
 	return strings.TrimSpace(string(answer)), nil
 }
+
+// Password prompts the user for a password. The prompt is written to out and
+// the answer is read from in.
+// The in reader has to be a terminal.
+func Password(ctx context.Context, out io.Writer, in SecureReader, question string) (string, error) {
+	if question != "" {
+		fmt.Fprintf(out, "%s:\n", question)
+	}
+	answer, err := in.ReadPassword(ctx)
+	if err != nil {
+		return "", trace.Wrap(err, "failed reading prompt response")
+	}
+	return string(answer), nil // passwords not trimmed
+}