Remove username prompt on buf registry login (#3128)

This removes the requirement to provide your username when calling `buf
registry login`. On login the token is validated by fetching the current
user. The username is used only to validate that the current token is
associated with the user but is otherwise redundant. The flag has now
been marked deprecated and is hidden.

The output of the login command is also updated to be more user friendly
prompting the user to visit the web UI to create a token if they do not
have one. On successful login the user is informed that they are logged
in as the current user.

CHANGELOG.md

@@ -5,6 +5,8 @@
 - Add `buf generate --clean` flag that will delete the directories, jar files, or zip files that the
   plugins will write to, prior to generation. Allows cleaning of existing assets without having
   to call `rm -rf`.
+- Deprecate `--username` flag on and username prompt on `buf registry login`. A username is no longer
+  required to log in.
 
 ## [v1.34.0] - 2024-06-21
 

private/buf/cmd/buf/command/registry/registrylogin/registrylogin.go

@@ -47,7 +47,7 @@ func NewCommand(
 	return &appcmd.Command{
 		Use:   name + " <domain>",
 		Short: `Log in to the Buf Schema Registry`,
-		Long: fmt.Sprintf(`This prompts for your BSR username and a BSR token and updates your %s file with these credentials.
+		Long: fmt.Sprintf(`This prompts for your BSR token and updates your %s file with these credentials.
 The <domain> argument will default to buf.build if not specified.`, netrc.Filename),
 		Args: appcmd.MaximumNArgs(1),
 		Run: builder.NewRunFunc(
@@ -73,8 +73,10 @@ func (f *flags) Bind(flagSet *pflag.FlagSet) {
 		&f.Username,
 		usernameFlagName,
 		"",
-		"The username to use. This command prompts for a username by default",
+		"The username to use.",
 	)
+	_ = flagSet.MarkDeprecated(usernameFlagName, "This flag is no longer needed as the username is automatically derived from the token")
+	_ = flagSet.MarkHidden(usernameFlagName)
 	flagSet.BoolVar(
 		&f.TokenStdin,
 		tokenStdinFlagName,
@@ -135,26 +137,15 @@ func inner(
 		remote = container.Arg(0)
 	}
 	// Do not print unless we are prompting
-	if flags.Username == "" && !flags.TokenStdin {
+	if !flags.TokenStdin {
 		if _, err := fmt.Fprintf(
 			container.Stdout(),
-			"Log in with your Buf Schema Registry username. If you don't have a username, create one at https://%s.\n\n",
+			"Enter the BSR token created at https://%s/settings/user.\n\n",
 			remote,
 		); err != nil {
 			return err
 		}
 	}
-	username := flags.Username
-	if username == "" {
-		var err error
-		username, err = bufcli.PromptUser(container, "Username: ")
-		if err != nil {
-			if errors.Is(err, bufcli.ErrNotATTY) {
-				return errors.New("cannot perform an interactive login from a non-TTY device")
-			}
-			return err
-		}
-	}
 	var token string
 	if flags.TokenStdin {
 		data, err := io.ReadAll(container.Stdin())
@@ -197,14 +188,11 @@ func inner(
 	if user == nil {
 		return errors.New("no user found for provided token")
 	}
-	if user.Username != username {
-		return errors.New("the username associated with the provided token does not match the provided username")
-	}
 	if err := netrc.PutMachines(
 		container,
 		netrc.NewMachine(
 			remote,
-			username,
+			user.Username,
 			token,
 		),
 	); err != nil {
@@ -217,9 +205,9 @@ func inner(
 	if err != nil {
 		return err
 	}
-	loggedInMessage := fmt.Sprintf("Credentials saved to %s.\n", netrcFilePath)
+	loggedInMessage := fmt.Sprintf("Logged in as %s. Credentials saved to %s.\n", user.Username, netrcFilePath)
 	// Unless we did not prompt at all, print a newline first
-	if flags.Username == "" || !flags.TokenStdin {
+	if !flags.TokenStdin {
 		loggedInMessage = "\n" + loggedInMessage
 	}
 	if _, err := container.Stdout().Write([]byte(loggedInMessage)); err != nil {