With Version 10 of Alteryx Server Gallery, if new user signup is disabled, people see the following when clicking the sign in button:
If someone tries to fill out the "Join Now" section they then get:
In Alteryx Server Version 9.5, when new user sign up was disabled, the join now section of the prompt was not present. This is our prefered behavior. Another option would be to change the "Access denied" message to something more descriptive such as "New user sign up disabled."
Thanks,
Ryan