Which user token should I send at query time? - userToken and authenticatedUserToken best practices

The user token sent with search queries must match the userToken parameter sent with events in order for Algolia's AI features to function efficiently. This means you should be sending the anonymous/session user token with search queries. If a userToken is not explicitly set at query time, Algolia defaults to setting one based on the request's IP address.
 
Our current recommendation is:

• Send the same anonymous/session userToken in both the search and events userToken parameters
• If a user logs in (authenticated users), send the authenticatedUserToken in the authenticatedUserToken events parameter
• Do not replace userToken with the authenticated user token in search queries or events 
• Following this means:
  • both the anonymous and authenticated user tokens will be sent with each event to ensure that data collected when users weren’t authenticated isn’t lost
  • user profiles for Personalisation continue to be updated, as profiles are currently built using userToken

More info on these parameters can be found here:

• User Token: https://www.algolia.com/doc/api-reference/api-parameters/userToken/#how-to-use
• Authenticated User Token: https://www.algolia.com/doc/guides/sending-events/concepts/usertoken/#authenticated-user-token

Useful Guides: 

• What is the best practice for identifying userTokens if a login is possible at any point in the customer journey?

For a full list of common userToken issues, troubleshooting topics and best practices, see our summary article here.