feat(web): optional web login and API tokens, off by default (stacked on #674) (#683)

Optional web login, off by default: a device that sets no password behaves
exactly as before. Set under General > Security; then every page and API
route needs a session login or an API token (Authorization: Bearer).
Loopback, the Wi-Fi setup flow in AP mode, static files, captive-portal
probes and a reduced /api/v3/health stay open. Secrets live in the web_auth
section of config_secrets.json and no API returns them.
scripts/reset_web_password.py turns login off. Stacked on #674.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

scripts/reset_web_password.py

@@ -0,0 +1,104 @@
+#!/usr/bin/env python3
+"""
+Turn the web interface's optional login off, for when the password is lost.
+
+Removes the password (and the key that signs login cookies) from the
+``web_auth`` section of ``config/config_secrets.json``. The interface is then
+open again, as it is before a password is ever set, and a new password can be
+set under General > Security. API tokens are kept unless ``--revoke-tokens``
+is given. Nothing else in the secrets file is touched, and the web service
+does not need a restart: it notices the change on the next request.
+
+Run it on the Pi, from any directory:
+
+    sudo python3 ~/LEDMatrix/scripts/reset_web_password.py
+
+``sudo`` because the secrets file is not readable by every user. The file
+keeps its owner and permissions.
+
+Another way in without the password: open the interface from the Pi itself
+(http://localhost:5000). Requests from the Pi are never asked to log in.
+"""
+import argparse
+import json
+import sys
+from pathlib import Path
+
+PROJECT_ROOT = Path(__file__).resolve().parent.parent
+sys.path.insert(0, str(PROJECT_ROOT))
+
+from src.config_manager_atomic import atomic_write_json  # noqa: E402
+
+SECTION = 'web_auth'   # web_interface/auth.py; not imported to keep Flask out
+LOGIN_KEYS = ('password_hash', 'session_secret', 'password_set_at')
+
+
+def reset(settings_file: Path, revoke_tokens: bool = False) -> str:
+    """Clear the login from ``settings_file`` (config_secrets.json).
+
+    Returns what was done. The message names the file and counts tokens; it
+    never includes anything read from the file.
+    """
+    if not settings_file.exists():
+        return f'{settings_file} does not exist, so no password is set. Nothing to do.'
+    with open(settings_file, 'r', encoding='utf-8') as fh:
+        data = json.load(fh)
+    if not isinstance(data, dict):
+        raise ValueError(f'{settings_file} does not hold a JSON object')
+
+    section = data.get(SECTION)
+    if not isinstance(section, dict):
+        return 'No web login password is set. Nothing to do.'
+
+    had_password = bool(section.get('password_hash'))
+    token_count = len(section.get('tokens') or [])
+    for key in LOGIN_KEYS:
+        section.pop(key, None)
+    if revoke_tokens:
+        section.pop('tokens', None)
+    if section:
+        data[SECTION] = section
+    else:
+        data.pop(SECTION, None)
+
+    if not had_password and not (revoke_tokens and token_count):
+        return 'No web login password is set. Nothing to do.'
+    atomic_write_json(settings_file, data)
+
+    done = []
+    if had_password:
+        done.append('Web login is off: the interface opens without a password. '
+                    'Set a new one under General > Security.')
+    if revoke_tokens and token_count:
+        done.append(f'Revoked {token_count} API token(s).')
+    elif token_count:
+        done.append(f'{token_count} API token(s) kept (use --revoke-tokens to remove them).')
+    return ' '.join(done)
+
+
+def main(argv=None) -> int:
+    parser = argparse.ArgumentParser(
+        description='Turn the LEDMatrix web login off (lost password recovery).')
+    parser.add_argument('--secrets', dest='settings_file', type=Path,
+                        default=PROJECT_ROOT / 'config' / 'config_secrets.json',
+                        help='secrets file (default: config/config_secrets.json '
+                             'in this LEDMatrix checkout)')
+    parser.add_argument('--revoke-tokens', action='store_true',
+                        help='also delete every API token')
+    args = parser.parse_args(argv)
+    settings_file = args.settings_file
+    try:
+        outcome = reset(settings_file, revoke_tokens=args.revoke_tokens)
+    except PermissionError:
+        print(f'Permission denied reading or writing {settings_file}. Run it with sudo.',
+              file=sys.stderr)
+        return 1
+    except (OSError, ValueError) as err:
+        print(f'Could not reset the web login: {err}', file=sys.stderr)
+        return 1
+    print(outcome)
+    return 0
+
+
+if __name__ == '__main__':
+    sys.exit(main())