Legacy set of service accounts that use Basic authentication with username and password to access the API/Services that we provide. These service accounts share email address depending on who is responsible to manage the passwords forming a many accounts to one email address relationship. We want to move all of these accounts into Auth0 and offer better authentication flows for existing and new services being developed but the unique email address requirement is preventing this migration. Many of these accounts are external clients/applications and are not expected to have resources to adapt to a new flow.
What is the recommended approach for migrating old service accounts like these that share a managing email address where they cannot be added as Applications to auth0?