User management in Jenkins
Security is all about authentication and authorization, which are parts of the AAA trio:

For security configuration, go to Manage Jenkins
and click on Configure Global Security
in Jenkins:

To enable security in Jenkins, click on Enable Security
. By default, security is enabled in Jenkins:

We need to change TCP port for JNLPagents
to Random
so agents can be configured.
For Access Control
in Authentication
, select Jenkins' own user database
in the Security Realm
section.
Check Allow users to sign up
so new users can create an account:

In Authorization
, select Matrix-based security
to provide rights to all available users as required:

We can also select Project-based matrix Authorization Strategy
. In this case, we need to go to the individual build job or project and go to its configuration:

Check Enable project-based security
and give rights to individual users:

It often happens that we accidently lock our Jenkins by not providing rights to admin users specifically and then...