If we write subdomain in the login, then this subdomain is not taken into account.

This is related to changes by this commit: https://github.com/jenkinsci/active-directory-plugin/commit/7c04f787b84cb7cd376ebb25d0b15ec649264c07

This is incorrect:
If people type in 'foo@bar' or 'bar\foo' or just 'foo', it should be treated as 'foo@bar' (where 'bar' represents the given domain name)

'bar' is represent a domain name which is set in the configuration, not in the login.

For example we set our Domain Name to 'bar.com'. Then we write login 'subbar\foo'. We expect to transform this to 'foo@subbar.bar.com'. But instead a 'foo@bar.com' is used.