Recently I ran into a frustrating issue in the Magento 2.2.4 installation phase where you connect your database, involving this error below:
1SQLSTATE[HY000]  The server requested authentication method unknown to the client
I was attempting to install Magento 2.2.4 on my macOS High Sierra running Apache 2 and MySQL 8.0.11, using PHP version 7.0.40 — which, according to the Magento 2.2 “readiness check”, shows that I should have had no issue. The problem with the Magento 2.2.4 readiness check is that it does not read the MySQL version that you are connecting to your store because the “readiness check” is one step before you go ahead and connect the database.
The quick solution here is to check your MySQL version to make sure it’s compatible with Magento 2. If you are not using MySQL 5.6 or 5.7, and you are using PHP version 7.0.40 then you are definitely going to run into the error message above.