title: How to Add auth_time claim in during jwt creation via help of SecurityTokenDescriptor and ClaimsIdentity
body: <p>I am creating my jwt from following code. What i needed is <code>auth_time</code> claim which would be like something like </p>
  
  <pre><code>   "nbf": 1582109929,
    "exp": 1582110229,
    "iat": 1582109929,
  </code></pre>
  
  <p>but I don't know how can I assign time value in above format or any way this claim automatically added with iat like value</p>
  
  <pre><code>public string GetIdTokenString(Dictionary&lt;string, object&gt; inputClaims, string secret)
      {
          string result = null;
          try
          {
              var tokenHandler = new JwtSecurityTokenHandler();
              var key = Encoding.ASCII.GetBytes(secret);
  
              List&lt;Claim&gt; claims = new List&lt;Claim&gt;();
              foreach (var o in inputClaims)
              {
                  string val = null;
                  if (o.Value != null)
                  {
                      Type t = o.Value.GetType();
                      bool isDict = t.IsGenericType /*&amp;&amp; t.GetGenericTypeDefinition() == typeof(Dictionary&lt;,&gt;)*/;
                      if (isDict)
                      {
                          val = JsonSerializer.Serialize(o.Value);
                      }
                      else
                      {
                          val = o.Value.ToString();
                      }
                  }
                  claims.Add(new Claim(o.Key, val));
              }
              claims.Add(new Claim("sub", Guid.NewGuid().ToString()));          
  
              var tokenDescriptor = new SecurityTokenDescriptor
              {
                  Subject = new ClaimsIdentity(claims),
                  Expires = DateTime.Now.AddSeconds(60 * 5),
                  SigningCredentials = new SigningCredentials(new SymmetricSecurityKey(key), SecurityAlgorithms.HmacSha256Signature),
                  Audience = ObjInitialRequest.JwtData.ContainsKey("client_id") ? ObjInitialRequest.JwtData["client_id"] : null,
                  Issuer = "...",//from well known configuration issuer
              };              
              var token = tokenHandler.CreateToken(tokenDescriptor);
              if (token != null &amp;&amp; token is JwtSecurityToken)
              {
                  result = (token as JwtSecurityToken).RawData;
              }
          }
          catch (Exception ex)
          {
              //Logger    
          }
          return result;
      }
  </code></pre>