Here Mudassar Ahmed Khan has explained with an example, how to build a responsive (Mobile Friendly) User Login Form inside Bootstrap Modal Popup in ASP.Net using C# and VB.Net.
The responsive Login Form has been implemented using Custom ASP.Net Membership and Forms Authentication.
This article will also explains how to perform validations for the Bootstrap User Login Form using HTML5 required validation attribute.
It also has the Remember Me CheckBox feature which allows user to save the credentials when he visits site next time.
Complete source code is attached at the end of article.