Adding domain to the login page

Open up the login.html file and add a new input named domain, as follows:

    //src/main/resources/templates/login.html

    ...
    <label for="username">Username</label>
    <input type="text" id="username" name="username"/>
    <label for="password">Password</label>
    <input type="password" id="password" name="password"/>
    <label for="domain">Domain</label>
    <input type="text" id="domain" name="domain"/>
    …

Now, a domain will be submitted when users attempt to log in. However, Spring Security is unaware of how to use that domain to create a DomainUsernamePasswordAuthenticationToken object and pass it into AuthenticationProvider. To fix this, we will need to create DomainUsernamePasswordAuthenticationFilter.