Vielen Dank an alle. Ich habe eine Basisimplementierung eines Json-Web-Tokens gefunden und diese mit der Google-Variante erweitert. Ich habe es immer noch nicht vollständig geklappt, aber es ist zu 97% da. Dieses Projekt hat seinen Dampf verloren, also wird dies hoffentlich jemand anderem helfen, einen guten Vorsprung zu erlangen:
Hinweis: Änderungen, die ich an der Basisimplementierung vorgenommen habe (ich kann mich nicht erinnern, wo ich sie gefunden habe), sind:
- HS256 geändert -> RS256
- Die Reihenfolge von JWT und Alg in der Kopfzeile wurde vertauscht. Ich bin mir nicht sicher, wer es falsch verstanden hat, Google oder die Spezifikation, aber Google nimmt es so, wie es unten ist.
public enum JwtHashAlgorithm
{
RS256,
HS384,
HS512
}
public class JsonWebToken
{
private static Dictionary<JwtHashAlgorithm, Func<byte[], byte[], byte[]>> HashAlgorithms;
static JsonWebToken()
{
HashAlgorithms = new Dictionary<JwtHashAlgorithm, Func<byte[], byte[], byte[]>>
{
{ JwtHashAlgorithm.RS256, (key, value) => { using (var sha = new HMACSHA256(key)) { return sha.ComputeHash(value); } } },
{ JwtHashAlgorithm.HS384, (key, value) => { using (var sha = new HMACSHA384(key)) { return sha.ComputeHash(value); } } },
{ JwtHashAlgorithm.HS512, (key, value) => { using (var sha = new HMACSHA512(key)) { return sha.ComputeHash(value); } } }
};
}
public static string Encode(object payload, string key, JwtHashAlgorithm algorithm)
{
return Encode(payload, Encoding.UTF8.GetBytes(key), algorithm);
}
public static string Encode(object payload, byte[] keyBytes, JwtHashAlgorithm algorithm)
{
var segments = new List<string>();
var header = new { alg = algorithm.ToString(), typ = "JWT" };
byte[] headerBytes = Encoding.UTF8.GetBytes(JsonConvert.SerializeObject(header, Formatting.None));
byte[] payloadBytes = Encoding.UTF8.GetBytes(JsonConvert.SerializeObject(payload, Formatting.None));
//byte[] payloadBytes = Encoding.UTF8.GetBytes(@"{"iss":"761326798069-r5mljlln1rd4lrbhg75efgigp36m78j5@developer.gserviceaccount.com","scope":"https://www.googleapis.com/auth/prediction","aud":"https://accounts.google.com/o/oauth2/token","exp":1328554385,"iat":1328550785}");
segments.Add(Base64UrlEncode(headerBytes));
segments.Add(Base64UrlEncode(payloadBytes));
var stringToSign = string.Join(".", segments.ToArray());
var bytesToSign = Encoding.UTF8.GetBytes(stringToSign);
byte[] signature = HashAlgorithms[algorithm](keyBytes, bytesToSign);
segments.Add(Base64UrlEncode(signature));
return string.Join(".", segments.ToArray());
}
public static string Decode(string token, string key)
{
return Decode(token, key, true);
}
public static string Decode(string token, string key, bool verify)
{
var parts = token.Split('.');
var header = parts[0];
var payload = parts[1];
byte[] crypto = Base64UrlDecode(parts[2]);
var headerJson = Encoding.UTF8.GetString(Base64UrlDecode(header));
var headerData = JObject.Parse(headerJson);
var payloadJson = Encoding.UTF8.GetString(Base64UrlDecode(payload));
var payloadData = JObject.Parse(payloadJson);
if (verify)
{
var bytesToSign = Encoding.UTF8.GetBytes(string.Concat(header, ".", payload));
var keyBytes = Encoding.UTF8.GetBytes(key);
var algorithm = (string)headerData["alg"];
var signature = HashAlgorithms[GetHashAlgorithm(algorithm)](keyBytes, bytesToSign);
var decodedCrypto = Convert.ToBase64String(crypto);
var decodedSignature = Convert.ToBase64String(signature);
if (decodedCrypto != decodedSignature)
{
throw new ApplicationException(string.Format("Invalid signature. Expected {0} got {1}", decodedCrypto, decodedSignature));
}
}
return payloadData.ToString();
}
private static JwtHashAlgorithm GetHashAlgorithm(string algorithm)
{
switch (algorithm)
{
case "RS256": return JwtHashAlgorithm.RS256;
case "HS384": return JwtHashAlgorithm.HS384;
case "HS512": return JwtHashAlgorithm.HS512;
default: throw new InvalidOperationException("Algorithm not supported.");
}
}
// from JWT spec
private static string Base64UrlEncode(byte[] input)
{
var output = Convert.ToBase64String(input);
output = output.Split('=')[0]; // Remove any trailing '='s
output = output.Replace('+', '-'); // 62nd char of encoding
output = output.Replace('/', '_'); // 63rd char of encoding
return output;
}
// from JWT spec
private static byte[] Base64UrlDecode(string input)
{
var output = input;
output = output.Replace('-', '+'); // 62nd char of encoding
output = output.Replace('_', '/'); // 63rd char of encoding
switch (output.Length % 4) // Pad with trailing '='s
{
case 0: break; // No pad chars in this case
case 2: output += "=="; break; // Two pad chars
case 3: output += "="; break; // One pad char
default: throw new System.Exception("Illegal base64url string!");
}
var converted = Convert.FromBase64String(output); // Standard base64 decoder
return converted;
}
}
Und dann meine google-spezifische JWT-Klasse:
public class GoogleJsonWebToken
{
public static string Encode(string email, string certificateFilePath)
{
var utc0 = new DateTime(1970,1,1,0,0,0,0, DateTimeKind.Utc);
var issueTime = DateTime.Now;
var iat = (int)issueTime.Subtract(utc0).TotalSeconds;
var exp = (int)issueTime.AddMinutes(55).Subtract(utc0).TotalSeconds; // Expiration time is up to 1 hour, but lets play on safe side
var payload = new
{
iss = email,
scope = "https://www.googleapis.com/auth/gan.readonly",
aud = "https://accounts.google.com/o/oauth2/token",
exp = exp,
iat = iat
};
var certificate = new X509Certificate2(certificateFilePath, "notasecret");
var privateKey = certificate.Export(X509ContentType.Cert);
return JsonWebToken.Encode(payload, privateKey, JwtHashAlgorithm.RS256);
}
}