@harry_12
Could please confirm the below things?
>> If that user is a local user (Means its created through ambari UI )?
If yes that user will not be able to login to your OS.
>> Where does this user belong to Is it coming from AD or Ldap?
>> Where you are trying to ssh? What server is that ?
>> Are you doing curl on Ambari URL and trying to access with that user?
If thats the case, then it should be able to curl.
>> Please attach some screenshot of this event to understand it better.