Agile Central - SSO with Exceptions authentication is allowing users to log into rally1.rallydev.com

Question:
The subscription settings for authentication are set to SSO with Exceptions, however users are still able to log into Agile Central using rally1.rallydev.com.  How is this possible?
Answer:
There must be at least one username entered into the exceptions list in order for this setting to block rally1.rallydev.com authentication.
Additional Information:
See the help pages for SSO setup for more information; https://help.rallydev.com/rally-advanced-security-and-administration#exceptions.