c# - 为 Firebase 生成 JWT

Question

我正在尝试为 Windows 上的 C# .NET 编写自定义 JWT token 生成器，以便在 Google Firebase 中使用。我从 StackOverflow 上的几个不同地方提取的源代码(我试图重新发现它们，这样我就可以归功于原作者并问几个额外的问题)，所以它有点像大杂烩。

在大多数情况下它似乎可以工作，但它似乎没有按预期生成有效的 (firebase) token 。这可能完全是因为我一开始不了解它应该如何工作，但如果我能从这里得到第二双世界级的优秀工程师的眼睛来指出我做错了什么并让事情正常进行，那就太好了。

代码如下:

// Token generator setup
using Newtonsoft.Json;
using System;
using System.IO;
using System.Web;
using System.Web.Configuration;

namespace myapp.Utils
{
    public class GoogleJsonWebToken
    {
        public static string Encode(string uid)
        {
            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(60).Subtract(utc0).TotalSeconds;

            var firebaseInfPath = HttpContext.Current.Server.MapPath(WebConfigurationManager.AppSettings["firebaseInf"]);
            var firebaseInfJsonContent = File.ReadAllText(firebaseInfPath);
            var firebaseInf = JsonConvert.DeserializeObject<dynamic>(firebaseInfJsonContent);
            var privateKey = (string)firebaseInf.private_key;

            var payload = new
            {
                iss = firebaseInf.client_email,
                scope = firebaseInf.client_email,
                aud = "https://identitytoolkit.googleapis.com/google.identity.identitytoolkit.v1.IdentityToolkit",
                exp = exp,
                uid = uid,
                iat = iat,
                claims = new { premium_account = true }
            };

            return myapp.Utils.JsonWebToken.Encode(payload, privateKey, JwtHashAlgorithm.RS256);
        }
    }
}

JWT哈希算法代码如下:

// JsonWebToken.cs
using Newtonsoft.Json;
using Newtonsoft.Json.Linq;
using System;
using System.Collections.Generic;
using System.Security.Cryptography;
using System.Text;

namespace myapp.Utils
{
    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)
        {
            var keyBytes = Encoding.UTF8.GetBytes(key);
            return Encode(payload, keyBytes, 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;
        }
    }
}

Answer 1

token 被拒绝的原因是因为它使用错误的算法签名:您使用的是 HMAC-SHA256(对称 key 加密算法)，而正确的 token 使用 RSA-SHA256(非对称或公钥/私钥)算法)。您可以在示例 token 的 header 中看到这一点:"alg": "RS256"

我建议使用 System.IdentityModel.Tokens.Jwt 中的类来大大简化您的代码:

public class GoogleJsonWebToken
{
    public static string Encode(string uid)
    {
        var firebaseInfPath = HttpContext.Current.Server.MapPath(WebConfigurationManager.AppSettings["firebaseInf"]);
        var firebaseInfJsonContent = File.ReadAllText(firebaseInfPath);
        var firebaseInf = JsonConvert.DeserializeObject<dynamic>(firebaseInfJsonContent);

        // NOTE: Replace this with your actual RSA public/private keypair!
        var provider = new RSACryptoServiceProvider(2048);
        var parameters = provider.ExportParameters(true);

        // Build the credentials used to sign the JWT
        var signingKey = new RsaSecurityKey(parameters);
        var signingCredentials = new SigningCredentials(signingKey, SecurityAlgorithms.RsaSha256);

        // Create a collection of optional claims
        var now = DateTimeOffset.UtcNow;
        var claims = new[]
        {
            new Claim(JwtRegisteredClaimNames.Sub, firebaseInf.client_email),
            new Claim(JwtRegisteredClaimNames.Iat, now.ToUnixTimeSeconds().ToString(), ClaimValueTypes.Integer64),
            new Claim("uid", uid, ClaimValueTypes.String), 
            new Claim("premium_account", "true", ClaimValueTypes.Boolean)
        };

        // Create and sign the JWT, and write it to a string
        var jwt = new JwtSecurityToken(
            issuer: firebaseInf.client_email,
            audience: "https://identitytoolkit.googleapis.com/google.identity.identitytoolkit.v1.IdentityToolkit",
            claims: claims,
            expires: now.AddMinutes(60).DateTime,
            signingCredentials: signingCredentials);
        return new JwtSecurityTokenHandler().WriteToken(jwt);
    }
}

使用虚拟 key ，此代码创建一个与您的示例 token 的 header 和有效负载模式相匹配的 token :

eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiJmaXJlYmFzZS1hdXRoLXRva2VuQHNheWVyLWNoYXQuaWFtLmdzZXJ2aWNlYWNjb3VudC5jb20iLCJpYXQiOjE0Njc4MzgwODUsInVpZCI6IjUyMTQiLCJwcmVtaXVtX2FjY291bnQiOnRydWUsImV4cCI6MTQ2Nzg2Njg4NSwiaXNzIjoiZmlyZWJhc2UtYXV0aC10b2tlbkBzYXllci1jaGF0LmlhbS5nc2VydmljZWFjY291bnQuY29tIiwiYXVkIjoiaHR0cHM6Ly9pZGVudGl0eXRvb2xraXQuZ29vZ2xlYXBpcy5jb20vZ29vZ2xlLmlkZW50aXR5LmlkZW50aXR5dG9vbGtpdC52MS5JZGVudGl0eVRvb2xraXQifQ.yMSGRpm4r3mPqiA9KnKVILVb8jT2Vbqcy4gvoLIugXnzLlw45F-GepAaBJK-j0-EN34WLsiLiLCRDJwW15TMasbrB1ZX3H4zd1by2GjZ1VmcUL8LITglICvs8CXkamjPjHeQUc4q--jhveKmTby8WHsH4b-HeiYoVl8JhxrAF13buNbiTq66dfvkl9q6mnyuKS_oyFB6_9WNphzHRa2BdJ51olq4qQsUNZ-nzOe4moHHjxpEzQfQpIe-QMJHdqojp9ukOW5eTMhFkQRPs3Bme4jpxIHPknC9j8YRvx_i0FbEJ8qAY2ujWcq80aC6YBKox55iP-AwfX_mEV7Tz14PBQ

您应该能够输入公钥/私钥对并使用上述代码生成有效的 JWT。