disable_drupal_login
This simple module just disables the stock Drupal username/password login, while keeping the `user.login` route in place. We had a need for this, while using the OpenID Connect module, to rely solely on our OpenID Connect supported SSO solution for authentication.
Features
This can be used for any solution where you rely on an external authentication/SSO identity provider, but still want to maintain the `/user/login` path. This simply removes the ability for new users to register, to use the password reset route, and they will no longer see the user login form.
Post-Installation
You'll want to make sure you have your separate login method setup prior to installing this module. After that though, just install and it'll remove the form and reset link from the `/user/login` page.
Additional Requirements
None, though you'll want to set up the external authentication (OpenID Connect, Social Auth, etc.) of your choosing prior to installing this module..
Recommended modules/libraries
OpenID Connect
Social Auth
Similar projects
I looked into other options, but they seemed to screw with the routing in some fashion; either hiding it or obfuscating it in some way. They were more about making it harder to user the Drupal login, not replacing it with an external authentication method.