It takes 5 steps to develop a custom SharePoint FBA login page.
1. In Visual Studio 2010, create a SharePoint Project, and add an Application Page. For our purpose, I have named the application page “Login”.
2. Let us go to the root directory of our FBA web application, in the _forms folder, copy the code from the Default page to the application page we have just created.
3. Let us make sure the Page directive on our application page is properly defined.
5. And lastly, let us set the Sign In Page URL of our FBA web application.