Login program in Python
The biggest problem you currently have is keeping the passwords in plain text - use a one-way irreversible hash function, like argon2 or bcrypt. 

Going even further, you should not be doing it yourself and instead trust something stable that have already proved itself of being mature and safe - like passlib library.

If you know that user authentication part is going to become more complicated, think about using a specialized User Directory like LDAP or Active Directory - there is a third-party ldap package that you can use for your client implementation. 

Also, when a password is entered, the input should be hidden - there is a getpass module specifically for this kind of use case. Also, look into getuser() function for the login prompt.



There are also different third-party libraries, like click or cement that might help in making building the CLI apps easier. Explore the other CLI libraries at the awesome-python list.