A Web Application's Login Form block includes an "Email me a sign in link" option alongside the normal password fields. A visitor enters their email, gets a link by email, and clicking it signs them in, no password needed.
How it behaves
The link expires after 15 minutes and only works once. If the account has two-factor authentication turned on (an authenticator app or an email code, see "Giving your app's users their own two-factor authentication"), clicking the link still asks for that second step, a magic link only proves someone controls the email address, not that they're the account holder who separately turned 2FA on.
Requesting a link always shows the same "check your email" message whether or not that address actually has an account, the same way "Forgot Password" already behaves, so a visitor can't use this to find out which emails are registered.
Tip: This needs your app's email delivery configured the same way signup confirmation and password reset emails already do, if that isn't set up yet, see the emails section of your Web Application's settings.