def step1(self, username, password):
self._check_initialized()<EOL>context = AtvSRPContext(<EOL>str(username), str(password),<EOL>prime=constants.PRIME_2048,<EOL>generator=constants.PRIME_2048_GEN)<EOL>self.session = SRPClientSession(<EOL>context, binascii.hexlify(self._auth_private).decode())<EOL>
First authentication step.