como colocar um tempo do expiração do token jwt em vbnet no postmnan code example

Example 1: JASON WEB TOKENS EM VBNET COM WINDOWS FORMS

{
  "iss": "JwtServer",
  "sub": "hrmanager",
  "email": "hrmanager@xyz.com",
  "jti": "e971bd9c-7655-41d5-9c49-fabc054dc466",
  "iat": 1503922683,
  "http://schemas.microsoft.com/ws/2008/06/identity/claims/role": [
    "Employee",
    "HR-Worker",
    "HR-Manager"
  ],
  "Department": [
    "HR",
    "HR"
  ],
  "nbf": 1503922683,
  "exp": 1503924483
}

Example 2: JASON WEB TOKENS EM VBNET COM WINDOWS FORMS

var headerAndPayload = base64Encode(header) + "." + base64Encode(payload);

var secretkey = "@everone:KeepitSecret!";

signature = HMACSHA256(headerAndPayload, secretkey);