According to https://book.cakephp.org/2.0/en/core-utility-libraries/security.html, if we want to use PHP 7.1, we need to install mcrypt from PECL.
I built PHP 7.1 from source using the --with-mcrypt flag. I have tested and I do have mcrypt working in PHP 7.1. I tried installing the PECL version of mcrypt like the CakePHP documentation says, but PECL tells me mcrypt is only for PHP 7.2 and it won’t install in 7.1. This makes sense since PHP 7.1 can be built with mcrypt support. Is the CakePHP documentation incorrect?