There are 2 methods to enable logins under your own domain:
1. Set up SSO (see how) and have your own login page.
2. If you do not want to set up SSO, then you can switch to the HTTP sign in page (can be set under "settings").
Why do you have to switch to the HTTP page if you do not setup SSO?
For security reasons, OneSky offers an HTTPS sign in page hosted by oneskyapp.com as default even you have setup your customized domain for the below reasons:
1. Sign in page requires clients to input confidential data including their password. We believe it would be best to have this data sent in a more secure way.
2. Facebook Connect only works under oneskyapp.com
However, we should not ask you for the SSL certificate, so HTTPS will not work under your own domain. You do not want to scare users from going to the translation site with the below warning. So switching to the HTTP sign in page will be an option.
To switch to use the HTTP sign-in page,
1. Go to "Site Settings"
2. Under "Domain Information", select "HTTP" as the "Sign in type"
The risk of your traffic being sniffed on a node between your ISP and the destination is remote. You would be one amongst millions and it takes a non-trivial amount of processing power at that level to perform packet inspection to identify packets carrying login information.
The real risk is at local network, as it has been pointed out. The 2 most common scenarios are:
SSL guards against sniffing, and it has another advantage you might not be aware of: SSL allows you be sure the entity receiving your passwords and other details is who you think it is.
If say you were victim of DNS poisoning where someone redirects you to a malicious site which looks exactly like the legitimate website, you would have no way of knowing. With SSL you would get a warning/error that the site does not have a valid certificate which would alert you that all is not as it should be.
Personally I tailor my passwords to whether or not information travels over HTTPS. I do this because it is inevitable that eventually I will need login over HTTP on a untrusted network.