So ...

Let's see the HOW part ...

I am going to use a tiny (60 KB) plugin called Temporary Login Without Password.

Here it is:

https://wordpress.org/plugins/temporary-login-without-passwo...

So let's see the usual speed tests ...

Here are my results before installing the plugin ...

... and the result after installing and activating the plugin:

No more comments needed I guess ...

So, let's see how it works ...