Case-insensitive authentication in Antarcticle

As a User I'd like to be able to log in to Antarcticle without warring about case of the letters so that it's easier to log in.

Acceptance Criteria

• In case there is already a single user in Antarcticle internal DB, then the username is treated in case-insensitive manner
• In case user is absent in Antarcticle internal DB, then Antarcticle should send authentication request to Poulpe and, if the request is successful, then user should be stored in Antarcticle DB without the loss of letter case
• If there is a single user in Antarctilce, but authentication failed, then request to Poulpe is send for authentication with exact data as was input in the log in form.
  • If user was authenticated successfully by Poulpe and the user in the response is exactly the same as in internal DB, then its password should be updated in Antarcticle DB
  • If user was authenticated successfully by Poulpe but the returned user is in different case, then Antarcticle should store additional user with different case in username.

The rest of authentication process stays the same - if user is not authenticated by Poulpe, then Antarcticle should respond with the error to user and the data should be not updated in Antarcticle DB.