@Override
    public Future<MailToken> saveToken(MailToken mailToken) {
        return toScala(doSaveToken(Token.fromScala(mailToken)).thenApply(Token::toScala));
    }
@ Override public Future < MailToken > saveToken ( MailToken mailToken ) { return toScala ( doSaveToken ( Token . fromScala ( mailToken ) ) . thenApply ( Token :: toScala ) ) ; }
Saves a token.  This is needed for users that
are creating an account in the system instead of using one in a 3rd party system.

Note: If you do not plan to use the UsernamePassword provider just provide en empty
implementation

@param mailToken The token to save
@return A string with a uuid that will be embedded in the welcome email.