newToken function
Mints a fresh bearer token: 32 bytes from the platform's secure random, base64url-encoded and unpadded.
Long enough that guessing is not a strategy, and URL-safe so it survives
being pasted into a config file, a header or a --token flag intact.
Implementation
String newToken() {
final random = Random.secure();
final bytes = Uint8List.fromList([
for (var i = 0; i < 32; i++) random.nextInt(256),
]);
return base64Url.encode(bytes).replaceAll('=', '');
}