Problem statement
Is it possible to add a custom login button to the New Universal Login experience?
Solution
Generally, we recommend adding the authentication provider as a connection in Auth0 if possible.
Otherwise, if you just want to add an arbitrary button you can use a page template (see Customize New Universal Login Pages) with your own JavaScript to inject the button once the widget has rendered. This is not a particularly clean solution since you are dynamically adding the button and relying on the widget DOM structure to remain the same.