sign function

Future<String> sign(dynamic payload, String secret, { String alg = 'HS256', })

Signs payload with secret and returns a compact JWT string.

payload may be a JwtPayload or a raw Map<String, dynamic>. alg defaults to 'HS256'; supported values: HS256, HS384, HS512.

// Positional
final token = await sign(payload, secret);

// With explicit algorithm
final token = await sign(payload, secret, alg: 'HS512');

Implementation

Future<String> sign(
  dynamic payload,
  String secret, {
  String alg = 'HS256',
}) async {
  final Map<String, dynamic> claims = switch (payload) {
    JwtPayload p => p.toMap(),
    Map<String, dynamic> m => m,
    _ => throw ArgumentError(
        'payload must be a JwtPayload or Map<String, dynamic>'),
  };

  final hmac = _hmacFor(alg, utf8.encode(secret));
  if (hmac == null) throw ArgumentError('Unsupported algorithm: $alg');

  final header = _b64url(utf8.encode(jsonEncode({'alg': alg, 'typ': 'JWT'})));
  final body = _b64url(utf8.encode(jsonEncode(claims)));
  final sig = _b64url(hmac.convert(utf8.encode('$header.$body')).bytes);

  return '$header.$body.$sig';
}