[v12] Use distinct prompts during Windows WebAuthn registration

lib/auth/webauthnwin/api.go

@@ -73,7 +73,7 @@ type makeCredentialRequest struct {
 }
 
 // Login implements Login for Windows Webauthn API.
-func Login(ctx context.Context, origin string, assertion *wanlib.CredentialAssertion, loginOpts *LoginOpts) (*proto.MFAAuthenticateResponse, string, error) {
+func Login(_ context.Context, origin string, assertion *wanlib.CredentialAssertion, loginOpts *LoginOpts) (*proto.MFAAuthenticateResponse, string, error) {
 	if origin == "" {
 		return nil, "", trace.BadParameter("origin required")
 	}
@@ -112,10 +112,7 @@ func Login(ctx context.Context, origin string, assertion *wanlib.CredentialAsser
 }
 
 // Register implements Register for Windows Webauthn API.
-func Register(
-	ctx context.Context,
-	origin string, cc *wanlib.CredentialCreation,
-) (*proto.MFARegisterResponse, error) {
+func Register(_ context.Context, origin string, cc *wanlib.CredentialCreation) (*proto.MFARegisterResponse, error) {
 	if origin == "" {
 		return nil, trace.BadParameter("origin required")
 	}
@@ -163,13 +160,21 @@ func Register(
 	}, nil
 }
 
+const defaultPromptMessage = "Using platform authenticator, follow the OS dialogs"
+
 var (
-	// PromptPlatformMessage is the message shown before Touch ID prompts.
-	PromptPlatformMessage = "Using platform authenticator, follow the OS dialogs"
+	// PromptPlatformMessage is the message shown before system prompts.
+	PromptPlatformMessage = defaultPromptMessage
+
 	// PromptWriter is the writer used for prompt messages.
 	PromptWriter io.Writer = os.Stderr
 )
 
+// ResetPromptPlatformMessage resets [PromptPlatformMessage] to its original state.
+func ResetPromptPlatformMessage() {
+	PromptPlatformMessage = defaultPromptMessage
+}
+
 func promptPlatform() {
 	if PromptPlatformMessage != "" {
 		fmt.Fprintln(PromptWriter, PromptPlatformMessage)
@@ -210,7 +215,7 @@ type DiagResult struct {
 
 // Diag runs a few diagnostic commands and returns the result.
 // User interaction is required.
-func Diag(ctx context.Context, promptOut io.Writer) (*DiagResult, error) {
+func Diag(ctx context.Context) (*DiagResult, error) {
 	res := &DiagResult{}
 	if !IsAvailable() {
 		return res, nil

tool/tsh/mfa.go

@@ -37,6 +37,7 @@ import (
 	"github.com/gravitational/teleport/lib/auth/touchid"
 	wanlib "github.com/gravitational/teleport/lib/auth/webauthn"
 	wancli "github.com/gravitational/teleport/lib/auth/webauthncli"
+	"github.com/gravitational/teleport/lib/auth/webauthnwin"
 	"github.com/gravitational/teleport/lib/client"
 	"github.com/gravitational/teleport/lib/defaults"
 	"github.com/gravitational/teleport/lib/utils"
@@ -350,6 +351,16 @@ func (c *mfaAddCommand) addDeviceRPC(ctx context.Context, tc *client.TeleportCli
 		if authChallenge == nil {
 			return trace.BadParameter("server bug: server sent %T when client expected AddMFADeviceResponse_ExistingMFAChallenge", resp.Response)
 		}
+
+		// Tweak Windows platform messages so it's clear we whether we are prompting
+		// for the *registered* or *new* device.
+		// We do it here, preemptively, because it's the simpler solution (instead
+		// of finding out whether it is a Windows prompt or not).
+		const registeredMsg = "Using platform authentication for *registered* device, follow the OS dialogs"
+		const newMsg = "Using platform authentication for *new* device, follow the OS dialogs"
+		defer webauthnwin.ResetPromptPlatformMessage()
+		webauthnwin.PromptPlatformMessage = registeredMsg
+
 		authResp, err := tc.PromptMFAChallenge(ctx, "" /* proxyAddr */, authChallenge, func(opts *client.PromptMFAChallengeOpts) {
 			opts.PromptDevicePrefix = "*registered* "
 		})
@@ -371,6 +382,8 @@ func (c *mfaAddCommand) addDeviceRPC(ctx context.Context, tc *client.TeleportCli
 		if regChallenge == nil {
 			return trace.BadParameter("server bug: server sent %T when client expected AddMFADeviceResponse_NewMFARegisterChallenge", resp.Response)
 		}
+
+		webauthnwin.PromptPlatformMessage = newMsg
 		regResp, regCallback, err := promptRegisterChallenge(ctx, tc.WebProxyAddr, c.devType, regChallenge)
 		if err != nil {
 			return trace.Wrap(err)

tool/tsh/winwebauthn.go

@@ -58,7 +58,12 @@ func (w *webauthnwinDiagCommand) run(cf *CLIConf) error {
 	if !diag.IsAvailable {
 		return nil
 	}
-	resp, err := webauthnwin.Diag(cf.Context, os.Stdout)
+
+	promptBefore := webauthnwin.PromptWriter
+	defer func() { webauthnwin.PromptWriter = promptBefore }()
+	webauthnwin.PromptWriter = os.Stderr
+
+	resp, err := webauthnwin.Diag(cf.Context)
 	// Abort if we got a nil diagnostic, otherwise print as much as we can.
 	if resp == nil {
 		return trace.Wrap(err)