Problem: The `mongodbatlas_teams` resource only works with email addresses of user accounts which are existing members of the organization at apply time¹, and Team memberships can't (yet?) be managed via Identity Federation (third-party SAML IdP). Solution: If there was a datasource using the "Get All Organization Users" API² to return a list of organization members, that data could be used to filter the `usernames` input attribute of the `mongodbatlas_teams` resource to only add valid users. Workaround: We're using a Python script as an external datasource to get the data needed to perform said filtering. ¹: An error is thrown when trying to add a user who hasn't logged into Atlas or isn't part of the organization: `401 (request "NOT_USER_ADMIN") The currently logged in user does not have the user administrator role for any group, team, or organization containing user.` ²: https://www.mongodb.com/docs/atlas/reference/api/organization-users-get-all-users/#get-all-organization-users