How to implement
In one single instance, i.e say (http://127.0.0.1:1880/), I must be able to log in with different users
Secondly,
When User X logins to http://127.0.0.1:1880/, X must be able to see only User X flows and catalogues
When User Y logins to http://127.0.0.1:1880/, Y must be able to see only User Y flows and catalogues
Asked and answered many times. It doesn't work like that I'm afraid. 1 instance is just that, 1 instance. If you want completely separate workspaces run separate instances. It is very easy to do (use command like options to launch additional instances - info is in the forum and documentation)
Ben Hardill blogged a create series of posts on how to create a multi-tenent Node-RED system . It is a proof of concept and would need further development but it shows what needs to be done to isolate users. Multi Tenant Node-RED – Ben's Place