1) on failed login
stay on the same page and show only a error message (without be redirected to the cb login page)

Possibly. You'd use the onLoginFailed trigger where the second variable (accessed with [var2]) is the return url. You'd use a redirect action on that trigger and set the URL to [var2]. Suggest trying this on the demo site.

2) on valid login
open a welcome page in a modal popup (and stay in the same page)

This it likely can't do. The reason for this is the user is redirected after successful login back to their previous location. The modal window is JS. The modal window JS would need to execute at the redirect destination, which may or may not have a trigger CB Auto Actions can act on to add your JS to open a modal window. If it was a static page then it's more likely you could do this.

3) autologin for the new registered users (after e-mail confirmation)

Yes, auto login is possible. Our demo site is utilizing this already for the quick login as buttons.

znort wrote: Hi Kyle
thank's for the answer:

1) on failed login
stay on the same page and show only a error message (without be redirected to the cb login page)

Possibly. You'd use the onLoginFailed trigger where the second variable (accessed with [var2]) is the return url. 
You'd use a redirect action on that trigger and set the URL to [var2]. Suggest trying this on the demo site.

As you suggest, I had done some tests but the redirect still go to cb login page, maybe I do something wrong !
The following is the last configuration that I tried without luck:

trigger -> onLoginFailed
type -> redirect
user -> manual
user variable -> variable 2
action -> URL return
(the error message work !)

Actually I don't understand how to "set the URL to [var2]"

I looked for some documetation but I don't found it. Can you explain me more explicit please?

Thank's

This is a presales forum.
If you have support questions, please use the Single Add-on support forum and whan you post please provide exact version of Joomla/CB/CB Auto Actions.

user -> manual
user variable -> variable 2

Leave this as Automatic. You need to set the URL parameter under Action to [var2].