ASP.net Identity management with Azure, in Web Form - asp.net

Question

I have a Webform ASP.net (in VB.net) that I want to add identity management too. I have added code that allows for the registration of users. But, I am stuck on how to log a user in. My application uses SSO with Azure Active Directory. What I would like to do is, after the user Authenticates with Azure, then use Identity management to see if the user is in the web system and if they have roles.
This site can be accessed by three types of users: 1) Internal folks who would have a local account as well as an Azure AD account, who act as admins for the site 2) Internal folks who authenticate with Azure AD, but will not have local accounts (i.e authenticated but with no roles) 3) External folks who will not authenticate with Azure AD and will not have local accounts
My questions is, how do I use Identity management, after the users authenticates with Azure AD? Here is my code:
Startup.Auth.vb:
Partial Public Class Startup
Dim appSettings = ConfigurationManager.AppSettings
Private realm As String
Private aadInstance As String
Private tenant As String
Private metadata As String
Private authority As String
Public Sub ConfigureAuth(app As IAppBuilder)
Dim appSettings = ConfigurationManager.AppSettings
realm = ConfigurationManager.AppSettings("ida:RPIdentifier")
aadInstance = ConfigurationManager.AppSettings("ida:AADInstance")
tenant = ConfigurationManager.AppSettings("ida:Tenant")
metadata = String.Format("{0}/FederationMetadata/2007-06/FederationMetadata.xml", aadInstance)
authority = String.Format(CultureInfo.InvariantCulture, aadInstance, tenant)
app.SetDefaultSignInAsAuthenticationType(CookieAuthenticationDefaults.AuthenticationType)
app.UseCookieAuthentication(New CookieAuthenticationOptions())
Dim authOption As WsFederationAuthenticationOptions = New WsFederationAuthenticationOptions()
Dim fn = Function(context)
context.HandleResponse()
context.Response.Redirect("Home/Error?message=" + context.Exception.Message)
Return Task.FromResult(0)
End Function
Dim auth_not As WsFederationAuthenticationNotifications = New WsFederationAuthenticationNotifications() With {
.AuthenticationFailed = fn
}
Dim auth_opt As WsFederationAuthenticationOptions = New WsFederationAuthenticationOptions() With {
.Wtrealm = realm,
.MetadataAddress = metadata,
.Notifications = auth_not
}
app.UseWsFederationAuthentication(auth_opt)
End Sub
End Class
Default.aspx.vb login click:
Public Sub SignIn()
Dim newAuth As AuthenticationProperties = New AuthenticationProperties()
newAuth.RedirectUri = "/"
HttpContext.Current.GetOwinContext().Authentication.Challenge(newAuth, WsFederationAuthenticationDefaults.AuthenticationType)
End Sub
The problem is, I don't know where to user the UserManager to get the logged in user, after the user gets redirected to our companies log in page, and they are redirected back to the site, with the returned Azure AD Username.