JWT

http://www.iocoder.cn/Fight/understanding-jwt/?self

1. • base64
     {
     "typ": "JWT",
     "alg": "HS256"
     }

2. • 转字符再加 base64
     {
     "iss": "John Wu JWT",
     "iat": 1441593502,
     "exp": 1441594722,
     "aud": "www.example.com",
     "sub": "jrocket@example.com",
     "from_user": "B",
     "target_user": "A"
     }

3. 对 1+2的结果进行 HS256 加密，并且有秘钥