Seems it's not possible to configure the additional identity plugin in Jenkins for merge the duplicate user
As Jenkins is missing a way to ensure users unicity(unique) since they are created from various sources: authentication method (LDAP in my case), code commits (Subversion, Mercurial, Git, ...).
Depending on the way the user is retrieved by Jenkins (from a commit on a given SCM or its authentication), multiple identities are created for the same real user.
As a consequence, some features are not fully or badly working (login, notifications, user's builds, continuous integration game, ...) and configuration of users is a pain as it must be done multiple times for each real user.
Still the required features are:
- a merging features. Allow to merge multiple Jenkins users into a single account.
- a user pattern per SCM. Allow to choose how to extract a username from a commit for each SCM and how to optionally match existing one instead of creating a new user.
- an id pattern per notification type. Allow to define how to generate the default id used for notification from the user data (from his jenkins id, his name, his scm id, ...): for instance, his mail or his jabber id, ...
Reference: [JENKINS-10258] Allow users unicity - Jenkins Jira
Solution is Jenkins 1.480 but this is still in Vulnerabilities state and have bug as well.
Jenkins 1.480 introduces an extension point to resolve jenkins user "canonical" ID when searching for user in Database by id or full name. This plugin uses this extension point to let user configure external identities as user properties.
You can reach out to Jenkins community or Support team to know the status or when they will final release
