Azure AD authentication in ASP.NET web forms

See more:

VB

ASP.NET

Azure

I have an ASP.Net Web Forms application in which I have been tasked with implementing Azure AD authentication.

It seems as if, while debugging the application in localhost, the prompt opens properly - it doesn't do any redirection, but I guess that's an issue with my code or Azure settings.

When I deploy the application on its production server on a third party host (not Azure), the authentication prompt will not open at all.

What could the cause of this be?

Below is the code I use for the authentication process

Imports Microsoft.Identity.Client
Imports Microsoft.VisualBasic

Public Class AuthenticationManager
    Private Shared app As PublicClientApplication

    Shared Sub New()

        Dim clientId As String = ConfigurationManager.AppSettings("ida:ClientId")
        Dim redirectUri As String = ConfigurationManager.AppSettings("ida:RedirectUri")
        Dim tenantId As String = ConfigurationManager.AppSettings("ida:Tenant")
        Dim authorityUri = "https://login.microsoftonline.com/" & tenantId
        Dim scopes As String() = New String() {"https://graph.microsoft.com/User.Read"}



        app = PublicClientApplicationBuilder.Create(clientId).WithAuthority(authorityUri).WithTenantId(tenantId).WithRedirectUri(redirectUri).Build()
    End Sub

    Public Function GetAuthenticationResult() As String
        Try
            Dim scopes As String() = New String() {"https://graph.microsoft.com/User.Read"}

            Dim result As Microsoft.Identity.Client.AuthenticationResult = app.AcquireTokenInteractive(scopes).WithPrompt(Prompt.ForceLogin).ExecuteAsync().Result
            Return result.Account.Username
        Catch ex As Exception
            Err.Clear()
            Return "-"
            Exit Function
        End Try

    End Function
End Class

Private Sub BtnConnectWithAzure_Click(sender As Object, e As EventArgs) Handles BtnConnectWithAzure.Click
        Dim t As New Threading.Thread(AddressOf AuthenticateUser)
        t.SetApartmentState(ApartmentState.STA)
        t.Start()
    End Sub

    Private Sub AuthenticateUser()
        System.Net.ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls11 Or SecurityProtocolType.Tls12
        Dim app As New AuthenticationManager
        Dim username As String = app.GetAuthenticationResult()

        If username <> "-" Then
            Response.Redirect(username) 'This could be a problematic part re: redirection            
        End If

    End Sub

What I have tried:

I initially thought this was an issue regarding blocked popups on the browser, but it doesn't seem to be related to that - it doesn't seem to be a permission issue in general. I haven't really found any other suggestions online on what could be causing the issue