Both the miniExtensions Form and Portal extensions give you the option to have your users pick login details from a list, instead of entering data manually. This can be useful when privacy isn't a main concern, or when using the login more like a record lookup (e.g. look up a product record from a catalog).
Field type limitation: The Allow users to search from existing values in the table option is not currently supported for linked record fields. If your login field is a linked record field, this toggle will not be available. For authentication, we recommend using the user's email address or another unique identifier instead of their name. Using an email address also lets you enable two-factor verification.
Here's how to set this up:
For Forms, ensure that the Login page option is selected under How do users access their records? in the Share section. Portals will always have the login page enabled.
For a Form, select Share in the Builder toolbar. For a Portal, open Users & Login.
Open Login Fields and select the login field.
Turn on Allow users to search from existing values in the table.
Your users will now see a magnifying glass icon above that login field that opens a list of possible values. This list can be filtered as described here.