PLAIN and LOGIN mechanisms refuse SSL encrypted requests

[bebleo]

When authenticating using the PLAIN and LOGIN authentication mechanisms over SSL/TLS authentication fails. It will succeed when running the server is using STARTTLS. The following test will fail:

def test_AUTH_LOGIN_success(mock_smtpd_use_starttls, smtpd, user):
    with SMTP(smtpd.hostname, smtpd.port) as client:
        client.starttls()
        code, resp = client.docmd('AUTH', f'LOGIN {encode(user.username)}')
        assert code == 334
        assert resp == bytes(encode('Password'), 'ascii')
        code, resp = client.docmd(f'{encode(user.password)}')
        assert code == 235

The following, however, fails:

def test_AUTH_LOGIN_failure(mock_smtpd_use_ssl, smtpd, user):
    with SMTP_SSL(smtpd.hostname, smtpd.port) as client:
        code, resp = client.docmd('AUTH', f'LOGIN {encode(user.username)}')
        assert code == 334
        assert resp == bytes(encode('Password'), 'ascii')
        code, resp = client.docmd(f'{encode(user.password)}')
        assert code == 235  # Fails here because the code is "538 Authentication required."