I use a password manager and have a browser plugin installed for it to simplify entering passwords into websites. I recently encountered a website (enterprise SaaS solution I use at work), which actively blocks password managers from auto-filling passwords. The plugin isn't able to populate the password field, and if I "force" the plugin to populate it, the site immediately deletes everything entered into the password field. The only way to enter the password is to manually type it into the field. The password complexity requirements are very high (minimum 16 chars, all four character classes, cannot reuse previous 10 passwords - at least passwords don't expire).
Looking in the browser console, I can see a string printed from javascript somewhere "Starting code to block password managers"
. When I type a password into the field, I can see an AJAX request being sent on every keypress. The request seems to be to an API endpoint and the content is encrypted locally, so I can't see what is being sent.
2FA is required to log into the website, with the only option for the second factor is their own mobile app (installed from the itunes app store or google play).
Leaving all other details aside, why would a website actively block password managers?
P.S. The site in question is not available over public internet - our corporate IP addresses had to be whitelisted by the provider.