Currently, any wiki with single sign on and a provisionning model will create users only when the user tries to log in / provision an account.

For example, on Wikimedia projects, as long as an user doesn't visit de.wikipedia, the account there doesn't exist.

What happens when the account username exists in the reference database, for Wikimedia SUL accounts, but not locally? Currently, it prints the userpage-userdoesnotexist-view message: user does not exist. Technically, this is true, the user doesn't exist locally.

Yet, this information isn't the most valuable and useful information we can give to the user. Worst, this information is misleading, as demonstrated on T152128 where the message was understood as a SUL bug.

Outside Wikimedia, this is interesting for any other authentication extension using unique usernames across sites, ie when the username on the wiki will be some fixed username from an existing database and not chosen by the user.

Suggested plan

• Add to MediaWiki core in the relevant interface a method to implement by the authentication extension to indicate if the account could exist
• Implement this in CentralAuth
• Document for authentication plugins author how they can implement this feature

Suggested temporary solution

Meanwhile it's implemented, for the Wikimedia cluster, we can improve the userpage-userdoesnotexist-view.
@Amqui suggests to add "on this project/wiki" and "check [[Special:CentralAuth]] to know if it's exist or not", I'add add globally.