Hi Sara,
> When hosting my app on a webserver is it possible to add an authentification interface using your login and password on AGOL? and if it's possible HOW ?
Yes this is possible.When using Web AppBuilder Developer Edition, you sign-into your ArcGIS Online organization to access data content (such as a web map) that you want to create a new web app for.
Ensure that the web map and its data contents are NOT shared with everyone. In other words, only share them with members of your ArcGIS Online organization.
When you're finished creating your web app, simply download the web app from the Developer Edition main page (e.g., the page that shows you all your web apps), unzip the file and place the contents onto your own web server. Next, register your web app with your ArcGIS Online organization,
Add items—ArcGIS Online Help | ArcGIS
(see the Add apps section)
Don't share the item listing of the web app with anyone, so it will not appear in the ArcGIS Online organization. The web app is hosted on your own web server. When someone accesses your web app URL and attempts to open it, they will be prompted to login to access the data content. I believe this is what you're looking for.
Hope this helps,
