PHP 8 deprecates openssl_free_key (actually openssl_pkey_free which it aliases) and automatically destroys the key instance when it goes out of scope.
(PHP 4 >= 4.2.0, PHP 5, PHP 7, PHP 8)
openssl_pkey_free — 释放一个私钥
key持有该密钥的资源。
没有返回值。
PHP 8 deprecates openssl_free_key (actually openssl_pkey_free which it aliases) and automatically destroys the key instance when it goes out of scope.
This function also frees public key resources as received with openssl_pkey_get_public().
Manual above should say: "Frees a pkey resource"