def login(self, username, password):
        """
        Authenticate with the server using a username and password

        This command is allowed in the Non-Authenticated state.  If the
        server supports the STARTTLS capability and our transport supports
        TLS, TLS is negotiated before the login command is issued.

        A more secure way to log in is to use C{startTLS} or
        C{authenticate} or both.

        @type username: L{str}
        @param username: The username to log in with

        @type password: L{str}
        @param password: The password to log in with

        @rtype: L{Deferred}
        @return: A deferred whose callback is invoked if login is successful
        and whose errback is invoked otherwise.
        """
        d = maybeDeferred(self.getCapabilities)
        d.addCallback(self.__cbLoginCaps, username, password)
        return d

        Authenticate with the server using a username and password

        This command is allowed in the Non-Authenticated state.  If the
        server supports the STARTTLS capability and our transport supports
        TLS, TLS is negotiated before the login command is issued.

        A more secure way to log in is to use C{startTLS} or
        C{authenticate} or both.

        @type username: L{str}
        @param username: The username to log in with

        @type password: L{str}
        @param password: The password to log in with

        @rtype: L{Deferred}
        @return: A deferred whose callback is invoked if login is successful
        and whose errback is invoked otherwise.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/mail/imap4.py