feat(auth): add disable-2fa command (#38275)

This PR adds the `gitea admin user disable-2fa` command to disable 2FA
for a user

When the only admin in the instance loses their 2FA credentials, this
command can be used to disable 2FA, allowing them to log in and reset
it.

---------

Co-authored-by: Giteabot <teabot@gitea.io>

cmd/admin_user_disable_2fa.go

@@ -0,0 +1,72 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package cmd
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"strings"
+
+	auth_model "gitea.dev/models/auth"
+	user_model "gitea.dev/models/user"
+	"gitea.dev/modules/setting"
+
+	"github.com/urfave/cli/v3"
+)
+
+func microcmdUserDisableTwoFactor() *cli.Command {
+	return &cli.Command{
+		Name:  "disable-2fa",
+		Usage: "Disable two-factor authentication for a user",
+		Flags: []cli.Flag{
+			&cli.StringFlag{
+				Name:    "username",
+				Aliases: []string{"u"},
+				Usage:   "Username of the user to disable 2FA for",
+			},
+			&cli.Int64Flag{
+				Name:  "id",
+				Usage: "ID of the user to disable 2FA for",
+			},
+		},
+		Action: runDisableTwoFactor,
+	}
+}
+
+func runDisableTwoFactor(ctx context.Context, c *cli.Command) error {
+	if !c.IsSet("id") && !c.IsSet("username") {
+		return errors.New("either --id or --username must be provided")
+	}
+
+	if !setting.IsInTesting {
+		if err := initDB(ctx); err != nil {
+			return err
+		}
+	}
+
+	var user *user_model.User
+	var err error
+	if c.IsSet("id") {
+		user, err = user_model.GetUserByID(ctx, c.Int64("id"))
+	} else {
+		user, err = user_model.GetUserByName(ctx, c.String("username"))
+	}
+	if err != nil {
+		return err
+	}
+
+	// When both selectors are given, make sure they refer to the same user.
+	if c.IsSet("id") && c.IsSet("username") && user.LowerName != strings.ToLower(strings.TrimSpace(c.String("username"))) {
+		return fmt.Errorf("the user with id %d is %q, which does not match the provided username %q", user.ID, user.Name, c.String("username"))
+	}
+
+	totp, webAuthn, err := auth_model.DisableTwoFactor(ctx, user.ID)
+	if err != nil {
+		return err
+	}
+
+	fmt.Printf("Disabled 2FA for user %q (removed %d TOTP and %d WebAuthn credential(s))\n", user.Name, totp, webAuthn)
+	return nil
+}