Best practice for migrating user ids

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Hi @victoryun,

Thanks for joining the Community!

Auth0 stores user IDs as {identity provider id}|{unique id in the provider} or facebook|1234567890. This way within a tenant, a user’s ID will be unique.

If you plan to use a Custom Database , then the most important thing would be to structure the ID in a way that the IDs will not collide, for example:

function login (email, password, callback) {
  var user = getUserFromDB(email);
  var profile = {
    user_id: 'MyConnection|' + user.id,
    email: user.email,
    [...]
  };
  callback(null, profile);
}

If you’re interested in how you might use a UUID in user metadata in order to identify users in a universally unique way (not just unique within a tenant), you can take a look at the answer in this topic: Using another user identifier (UUID) than the user_id - #2 by jmangelo

Please let me know if that is the info you’re looking for. Thanks!