JWT Token由以下三部分组成：

• HEADER:ALGORITHM & TOKEN TYPE

  json { "alg": "HS256", "typ": "JWT" }

• PAYLOAD:DATA

  json { "sub": "1234567890", "name": "John Doe", "iat": 1516239022 }

• VERIFY SIGNATURE

  json HMACSHA256( base64UrlEncode(header) + "." + base64UrlEncode(payload), your-256-bit-secret )