The prompt does not have clarity about which password the user should use for registration.

[LalatenduMohanty]

As we are encouraging users to register in http://developers.redhat.com/ and use the password for registering CDK to RHN , the prompt should clearly communicate it to the user. In current state user might get confused which user name/password he supposed to enter. The ideal solution would be using the same terminology as official CDK documentation

$ vagrant up

xxxxxxxxxxxxxxxxx

==> default: Registering box with vagrant-registration...
    default: Would you like to register the system now (default: yes)? [y|n]y
    default: username: 

[LalatenduMohanty]

vagrant-registration can support multiple subscription managers. Currently it uses only Red Hat subscription manager as the default one.
So the code needs to be modified to detect the subscription manager and then choose the statement for user.

default: Would you like to register the system now (default: yes)? [y|n]y
default: Please use your Red Hat account for registration. 
default: Login: 
default: Password: