Actual behaviour

As user "A" when configuring authorization
using the "Run as Specific User" strategy to run a job as user "B"
after successful authentication with the password of user "B"
user "A" is logged out.

Expected behaviour

User "A" is still logged in.

Root Cause Analysis

This issue is present starting with Jenkins 2.150.2 which implemented new security measures for user sessions (see changelog https://jenkins.io/changelog-stable/#v2.150.2). It seems that the below call from here invalidates the current user session:

Jenkins.getActiveInstance().getSecurityRealm().getSecurityComponents().manager.authenticate(
    new UsernamePasswordAuthenticationToken(userId, password)
);