I need to be able to integrate Chargify subscriptions via API with my vb.net webforms site

Question

There is almost no documentation for implementing Chargify as the Authentication provider for a vb.net webforms application.

I need to be able to have my customers 1)Browse to my introduction page, 2)Click the register link and be carried to a public signup page at Chargify, 3)Register with First Name, Last Name, Email Address 4)Pay for their subscription, 5)Be sent back to my page as an authenticated user. Chargify provides an API for this and an API key. I just don't know how/where this need to be used. I can find no documentation for this in vb.net webforms. I am currently trying to implement it into the stock template vb.net webforms app in Visual Studio 2017. I think that I have found where to start but am not sure where or how to proceed. Any guidance or a reference/example would be appreciated. Below is where I think I should possibly start.

Public Sub ConfigureAuth(app As IAppBuilder)
        'Configure the db context, user manager and signin manager to use a single instance per request
        app.CreatePerOwinContext(AddressOf ApplicationDbContext.Create)
        app.CreatePerOwinContext(Of ApplicationUserManager)(AddressOf ApplicationUserManager.Create)
        app.CreatePerOwinContext(Of ApplicationSignInManager)(AddressOf ApplicationSignInManager.Create)

        ' Enable the application to use a cookie to store information for the signed in user
        app.UseCookieAuthentication(New CookieAuthenticationOptions() With {
            .AuthenticationType = DefaultAuthenticationTypes.ApplicationCookie,
            .Provider = New CookieAuthenticationProvider() With {
                .OnValidateIdentity = SecurityStampValidator.OnValidateIdentity(Of ApplicationUserManager, ApplicationUser)(
                    validateInterval:=TimeSpan.FromMinutes(30),
                    regenerateIdentity:=Function(manager, user) user.GenerateUserIdentityAsync(manager))},
            .LoginPath = New PathString("/Account/Login")})
        ' Use a cookie to temporarily store information about a user logging in with a third party login provider
        app.UseExternalSignInCookie(DefaultAuthenticationTypes.ExternalCookie)

        ' Enables the application to temporarily store user information when they are verifying the second factor in the two-factor authentication process.
        app.UseTwoFactorSignInCookie(DefaultAuthenticationTypes.TwoFactorCookie, TimeSpan.FromMinutes(5))

        ' Enables the application to remember the second login verification factor such as phone or email.
        ' Once you check this option, your second step of verification during the login process will be remembered on the device where you logged in from.
        ' This is similar to the RememberMe option when you log in.
        app.UseTwoFactorRememberBrowserCookie(DefaultAuthenticationTypes.TwoFactorRememberBrowserCookie)

        ' Uncomment the following lines to enable logging in with third party login providers
        'app.UseMicrosoftAccountAuthentication(
        '    clientId:= "",
        '    clientSecret:= "")

        'app.UseTwitterAuthentication(
        '   consumerKey:= "",
        '   consumerSecret:= "")

        'app.UseFacebookAuthentication(
        '   appId:= "",
        '   appSecret:= "")

        'app.UseGoogleAuthentication(New GoogleOAuth2AuthenticationOptions() With {
        '   .ClientId = "",
        '   .ClientSecret = ""})
    End Sub

I would like to know where/how to setup authentication via API and Chargify for a vb.net webforms app.