Add support for custom fields on the login page

[Badgerati]

Description of the Change

This adds a new -Content parameter to Set-PodeWebLoginPage which allows for the overriding of fields displayed on the login page.

By default, the fields will still be Username and Password, but if -Content is supplied then these fields will be used instead. The content can be any Layout or Element, and will be place within a Form between the "Please sign in" message and the "Sign in" button.

A new -SignInMessage parameter has also been added to Set-PodeWebLoginPage, which allows the "Please sign in" message to be customised.

Further, there are 2 new switches for New-PodeWebTextbox: -AutoFocus and -DynamicLabel. If AutoFocus is supplied then the textbox will be automatically focused on page load. DynamicLabel enables the feature that the textboxes on the login page have, whereby the placeholder/label for the textbox will seemingly "float" and "shrink" to the top of the textbox when input is given.

Examples

# setup sessions
Enable-PodeSessionMiddleware -Duration 120 -Extend
# define a new custom authentication scheme, which needs a client, username, and password
$custom_scheme = New-PodeAuthScheme -Custom -ScriptBlock {
    param($opts)
    # get the client/user/password from the request's post data
    $client = $WebEvent.Data.client
    $username = $WebEvent.Data.username
    $password = $WebEvent.Data.password
    # return the data in a array, which will be passed to the validator script
    return @($client, $username, $password)
}
# now, add a new custom authentication validator using the scheme you created above
$custom_scheme | Add-PodeAuth -Name Example -ScriptBlock {
    param($client, $username, $password)
    # check if the client is valid in some database
    return @{
        User = @{
            ID ='M0R7Y302'
            Name = 'Morty'
            Type = 'Human'
        }
    }
    # return a user object (return $null if validation failed)
    return  @{ User = $user }
}
# set the login page to use the custom auth, and also custom login fields
Set-PodeWebLoginPage -Authentication Example -Content @(
    New-PodeWebTextbox -Type Text -Name 'client' -Id 'client' -Placeholder 'Client' -Required -AutoFocus -DynamicLabel
    New-PodeWebTextbox -Type Text -Name 'username' -Id 'username' -Placeholder 'Username' -Required -DynamicLabel
    New-PodeWebTextbox -Type Password -Name 'password' -Id 'password' -Placeholder 'Password' -Required -DynamicLabel
)