What is JWT? A brief understanding of JWT

<?php
require_once &#39;src/JWT.php&#39;;
header(&#39;Content-type:application/json&#39;);
//定义Key
const KEY = &#39;dasjdkashdwqe1213dsfsn;p&#39;;

$user = [
    &#39;uid&#39;=>&#39;dadsa-12312-vsd1s1-fsds&#39;,
    &#39;account&#39;=>&#39;daisc&#39;,
    &#39;password&#39;=>&#39;123456&#39;
];
$redis = redis();
$action  =  $_GET[&#39;action&#39;];
switch ($action)
{
    case &#39;login&#39;:
        login();
        break;
    case &#39;info&#39;:
        info();
        break;

}
//登陆，写入验证token
function login()
{
    global  $user;
    $account = $_GET[&#39;account&#39;];
    $pwd = $_GET[&#39;password&#39;];
    $res = [];
    if($account==$user[&#39;account&#39;]&&$pwd==$user[&#39;password&#39;])
    {
        unset($user[&#39;password&#39;]);
        $time = time();
        $token = [
            &#39;iss&#39;=>&#39;http://test.cc&#39;,//签发者
            &#39;iat&#39;=>$time,
            &#39;exp&#39;=>$time+60,
            &#39;data&#39;=>$user
        ];
        $jwt = \Firebase\JWT\JWT::encode($token,KEY);
        $res[&#39;code&#39;] = 200;
        $res[&#39;message&#39;] = &#39;登录成功&#39;;
        $res[&#39;jwt&#39;] = $jwt;

    }
    else
    {
        $res[&#39;message&#39;]= &#39;用户名或密码错误&#39;;
        $res[&#39;code&#39;] = 401;
    }
    exit(json_encode($res));
}





function info()
{
   $jwt = $_SERVER[&#39;HTTP_AUTHORIZATION&#39;] ?? false;
   $res[&#39;code&#39;] = 200;
   if($jwt)
   {
        $jwt = str_replace(&#39;Bearer &#39;,&#39;&#39;,$jwt);
        if(empty($jwt))
        {
            $res[&#39;code&#39;] = 401;
            $res[&#39;msg&#39;] = &#39;You do not have permission to access.&#39;;
            exit(json_encode($res));
        }
        try{
            $token = (array) \Firebase\JWT\JWT::decode($jwt,KEY, [&#39;HS256&#39;]);
            if($token[&#39;exp&#39;]<time())
            {
                $res[&#39;code&#39;] = 401;
                $res[&#39;msg&#39;] = &#39;登录超时，请重新登录&#39;;
            }
            $res[&#39;data&#39;]= $token[&#39;data&#39;];
        }catch (\Exception $E)
        {
            $res[&#39;code&#39;] = 401;
            $res[&#39;msg&#39;] = &#39;登录超时，请重新登录.&#39;;
        }
   }
   else
   {
       $res[&#39;code&#39;] = 401;
       $res[&#39;msg&#39;] = &#39;You do not have permission to access.&#39;;
   }
    exit(json_encode($res));
}



//连接redis
function redis()
{
    $redis = new  Redis();
    $redis->connect(&#39;127.0.0.1&#39;);
    return $redis;
}

    */
    public static function encode($payload, $key, $alg = 'HS256', $keyId = null, $head = null)
    {
        $header = array('typ' => 'JWT', 'alg' => $alg);
        if ($keyId !== null) {
            $header['kid'] = $keyId;
        }
        if ( isset($head) && is_array($head) ) {
            $header = array_merge($head, $header);
        }
        $segments = array();
        $segments[] = static::urlsafeB64Encode(static::jsonEncode($header));
        $segments[] = static::urlsafeB64Encode(static::jsonEncode($payload));
        $signing_input = implode('.', $segments);

        $signature = static::sign($signing_input, $key, $alg);
        $segments[] = static::urlsafeB64Encode($signature);

        return implode('.', $segments);
    }

 $token   = [
            #非必须。issuer 请求实体，可以是发起请求的用户的信息，也可是jwt的签发者。
            "iss"       => "http://example.org",
            #非必须。issued at。 token创建时间，unix时间戳格式
            "iat"       => $_SERVER['REQUEST_TIME'],
            #非必须。expire 指定token的生命周期。unix时间戳格式
            "exp"       => $_SERVER['REQUEST_TIME'] + 7200,
            #非必须。接收该JWT的一方。
            "aud"       => "http://example.com",
            #非必须。该JWT所面向的用户
            "sub"       => "jrocket@example.com",
            # 非必须。not before。如果当前时间在nbf里的时间之前，则Token不被接受；一般都会留一些余地，比如几分钟。
            "nbf"       => 1357000000,
            # 非必须。JWT ID。针对当前token的唯一标识
            "jti"       => '222we',
            # 自定义字段
            "GivenName" => "Jonny",
            # 自定义字段
            "name"   => "Rocket",
            # 自定义字段
            "Email"     => "jrocket@example.com",
         
        ];