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There are several options to uniquely identify your users:
  1. By the user_id property. This is guaranteed to be unique (within a tenant) per user (such as {identity provider id}|{unique id in the provider} or facebook|1234567890). A user may have the same user_id property across multiple Auth0 tenants, but consistency is not guaranteed. For regular and custom database connections, avoid creating duplicate user_ids within a tenant for different database connections. If you expect possible collisions between IDs from different connections, use a prefix identifying the connection.
  2. By a natural key, like the email property. We recommend that you use an IdP that requires users to verify their emails and then enable email verification in Auth0. Some IdPs, like Azure AD, can’t guarantee emails are verified. In this case, you can set up email verification for Azure AD and ADFS or implement external user verification with Auth0 Forms.