Dart implementation of https://oauth.net/core/1.0a

oauth.dart

import 'dart:convert';
import 'dart:math';
import 'package:crypto/crypto.dart';
import 'package:kaiteki/model/http_method.dart';

final DateTime _epoch = DateTime(1970);

/// Returns the seconds since January 1st 1970, required for the timestamp
/// parameter.
int secondsSinceEpoch() {
  return (DateTime.now().difference(_epoch)).inSeconds;
}

/// Generates a random string of characters, required for the nonce parameter.
String generateNonce([int length = 32]) {
  final random = Random.secure();
  const chars =
      'AaBbCcDdEeFfGgHhIiJjKkLlMmNnOoPpQqRrSsTtUuVvWwXxYyZz1234567890';
  final buffer = StringBuffer();

  for (var i = 0; i < length; i++) {
    final j = random.nextInt(chars.length - 1);
    buffer.write(chars[j]);
  }

  return buffer.toString();
}

/// Generates a signature with HMAC-SHA1.
String generateHmacSha256Signature(
  HttpMethod method,
  Uri url,
  Map<String, String> parameters,
  String secret,
) {
  final encodedSecret = encode(secret);
  final key = utf8.encode(encodedSecret + "&");
  final hmac = Hmac(sha1, key);
  final data = getSignatureString(method, url, parameters);
  final digest = hmac.convert(utf8.encode(data));
  return base64.encode(digest.bytes);
}

String getSignatureString(
  HttpMethod method,
  Uri url,
  Map<String, String> parameters,
) {
  final paramStr = parameters.entries //
      .map((kv) => kv.key + "=" + encode(kv.value))
      .join("&");

  final normalizedUrl = normalizeUrl(url);
  return [
    method.toMethodString(),
    encode(normalizedUrl),
    encode(paramStr),
  ].join("&");
}

String encode(String value) {
  final buffer = StringBuffer();
  final regex = RegExp("[0-9A-Za-z-._~]");

  for (var i = 0; i < value.length; i++) {
    final char = value[i];

    if (regex.hasMatch(char)) {
      buffer.write(char);
    } else {
      for (final byte in utf8.encode(char)) {
        final hex = byte.toRadixString(16).padLeft(2, '0').toUpperCase();
        buffer
          ..write("%")
          ..write(hex);
      }
    }
  }

  return buffer.toString();
}

String normalizeUrl(Uri url) {
  final scheme = url.scheme.toLowerCase();

  final isRedundantPort = (scheme == "http" && url.port == 80) ||
      (scheme == "https" && url.port == 443);

  return Uri(
    scheme: url.scheme,
    host: url.host,
    port: isRedundantPort ? null : url.port,
    path: url.path,
  ).toString().toLowerCase();
}

/// Returns a complete authorization header for OAuth v1.
///
/// Automatically adds missing parameters like nonce, signature and timestamp.
String generateAuthorizationHeader(
  HttpMethod method,
  Uri url,
  Map<String, String> parameters,
  String secret,
) {
  parameters.addAll({
    "oauth_nonce": generateNonce(),
    "oauth_version": "1.0",
    "oauth_timestamp": secondsSinceEpoch().toString(),
    "oauth_signature_method": "HMAC-SHA1",
  });

  parameters = _sortMap(parameters); // Sort properly before generating sig

  parameters["oauth_signature"] = generateHmacSha256Signature(
    method,
    url,
    parameters,
    secret,
  );

  parameters = _sortMap(parameters); // Sort properly before generating sig

  return getAuthorizationHeader(parameters);
}

String getAuthorizationHeader(Map<String, String> parameters) {
  final buffer = StringBuffer("OAuth ")
    ..writeAll(
      parameters.entries.map(
        (kv) => kv.key + '="' + encode(kv.value) + '"',
      ),
      ", ",
    );
  return buffer.toString();
}

Map<T1, T2> _sortMap<T1 extends Comparable, T2>(Map<T1, T2> map) {
  final sortedEntries = map.entries.toList()
    ..sort((a, b) => a.key.compareTo(b.key));

  return Map<T1, T2>.fromEntries(sortedEntries);
}