From 6f4b0fabcd4a4ffc9d71e69d85284f1e7b5eabe1 Mon Sep 17 00:00:00 2001
From: Lev Khobotov <l.hobotov@smartcat.ai>
Date: Wed, 20 Mar 2024 23:14:05 +0300
Subject: [PATCH] Fix JWT deserialization

---
 Amphasis.Azure.WebPortal/Helpers/JwtHelper.cs | 40 +++++++++++++++++++
 .../SimaLand/Services/SimaLandService.cs      | 12 +++---
 2 files changed, 46 insertions(+), 6 deletions(-)
 create mode 100644 Amphasis.Azure.WebPortal/Helpers/JwtHelper.cs

diff --git a/Amphasis.Azure.WebPortal/Helpers/JwtHelper.cs b/Amphasis.Azure.WebPortal/Helpers/JwtHelper.cs
new file mode 100644
index 0000000..91f1c3e
--- /dev/null
+++ b/Amphasis.Azure.WebPortal/Helpers/JwtHelper.cs
@@ -0,0 +1,40 @@
+using System;
+using System.Text.Json;
+using Microsoft.AspNetCore.WebUtilities;
+
+namespace Amphasis.Azure.WebPortal.Helpers;
+
+public static class JwtHelper
+{
+	public static DateTime GetValidTo(string encodedJsonWebToken)
+	{
+		var destination = new Span<Range>(new Range[3]);
+		var partsCount = encodedJsonWebToken.AsSpan().Split(destination, '.');
+
+		if (partsCount < 3)
+			throw new JwtHelperException("Could not extract payload");
+
+		var payloadRange = destination[1];
+		var (offset, count) = payloadRange.GetOffsetAndLength(encodedJsonWebToken.Length);
+		var bytes = WebEncoders.Base64UrlDecode(encodedJsonWebToken, offset, count);
+		var payload = JsonSerializer.Deserialize<JwtPayload>(bytes, _jsonSerializerOptions);
+
+		return DateTime.UnixEpoch.AddSeconds(payload.Exp);
+	}
+
+	static JwtHelper()
+	{
+		_jsonSerializerOptions = new JsonSerializerOptions {PropertyNamingPolicy = JsonNamingPolicy.CamelCase};
+	}
+
+	private static readonly JsonSerializerOptions _jsonSerializerOptions;
+
+	private sealed class JwtHelperException : Exception
+	{
+		public JwtHelperException(string message) : base(message)
+		{
+		}
+	}
+
+	private sealed record JwtPayload(int Exp);
+}
diff --git a/Amphasis.Azure.WebPortal/SimaLand/Services/SimaLandService.cs b/Amphasis.Azure.WebPortal/SimaLand/Services/SimaLandService.cs
index fc64158..0645e5b 100644
--- a/Amphasis.Azure.WebPortal/SimaLand/Services/SimaLandService.cs
+++ b/Amphasis.Azure.WebPortal/SimaLand/Services/SimaLandService.cs
@@ -1,11 +1,11 @@
 using System;
 using System.Collections.Generic;
 using System.ComponentModel;
-using System.IdentityModel.Tokens.Jwt;
 using System.IO;
 using System.Net.Http;
 using System.Threading.Tasks;
 using Amphasis.Azure.WebPortal.Extensions;
+using Amphasis.Azure.WebPortal.Helpers;
 using Amphasis.Azure.WebPortal.SimaLand.Models;
 using Amphasis.Azure.WebPortal.SimaLand.Models.Enums;
 using Amphasis.SimaLand;
@@ -15,7 +15,7 @@
 
 namespace Amphasis.Azure.WebPortal.SimaLand.Services
 {
-    public class SimaLandService
+	public class SimaLandService
     {
         private const string ApiClientAccessTokenKey = nameof(ApiClientAccessTokenKey);
         private static readonly TimeSpan TokenExpirationSkew = TimeSpan.FromSeconds(30);
@@ -74,10 +74,10 @@ private async ValueTask AuthorizeAsync()
         }
 
         private async Task<string> TokenFactoryAsync(ICacheEntry cacheEntry)
-        {
-            string token = await _apiClient.GetAccessTokenAsync(_configuration.Email, _configuration.Password);
-            var jwtSecurityToken = new JwtSecurityToken(token);
-            cacheEntry.AbsoluteExpiration = jwtSecurityToken.ValidTo - TokenExpirationSkew;
+        { 
+            var token = await _apiClient.GetAccessTokenAsync(_configuration.Email, _configuration.Password);
+            var validTo = JwtHelper.GetValidTo(token);
+            cacheEntry.AbsoluteExpiration = validTo - TokenExpirationSkew;
 
             return token;
         }