How would I update this to use Azure VPN Gateway?

[RudyD]

I would like to use best practices. I don't have express route. Was planning on Azure VPN Gateway to connect via the Azure VPN Client. I made a first pass, by putting the gateway in the hub vnet, but ran into connectivity issues as I was attempting to access eastus.pl-auth.privatelink.azuredatabricks.net (I had to move all resources to eastus closer to me). Anyway, the issue I ran into was the below. But unlike other custom apps, I don't have an app registration I can update the redirect URI (all I see is a single enterprise app record).

Any advice is appreciated.

AADSTS50011: The redirect URI 'https://eastus.pl-auth.privatelink.azuredatabricks.net/login.html' specified in the request does not match the redirect URIs configured for the application '2ff814a6-3304-4ab8-85cb-cd0e6f879c1d'. Make sure the redirect URI sent in the request matches one added to your application in the Azure portal. Navigate to https://aka.ms/redirectUriMismatchError to learn more about how to fix this.

Below is my current scripts:

vpn_gateway.tf

# --- VPN Gateway Configuration ---

# Create a public IP address for VPN Gateway
resource "azurerm_public_ip" "vpn_gateway_ip" {
  name                = "vpnGatewayPublicIP"
  location            = azurerm_resource_group.this.location
  resource_group_name = azurerm_resource_group.this.name
  allocation_method   = "Dynamic"
  sku                 = "Basic"
}

# Create the VPN Gateway
resource "azurerm_virtual_network_gateway" "vpn_gateway" {
  name                = "vpnGateway"
  location            = azurerm_resource_group.this.location
  resource_group_name = azurerm_resource_group.this.name

  type     = "Vpn"
  vpn_type = "RouteBased"
  sku      = "VpnGw1"

  ip_configuration {
    name                          = "vpnGatewayConfig"
    public_ip_address_id          = azurerm_public_ip.vpn_gateway_ip.id
    private_ip_address_allocation = "Dynamic"
    subnet_id                     = azurerm_subnet.hubvpngw.id # Referencing the GatewaySubnet here
  }

  vpn_client_configuration {
    address_space = ["172.16.0.0/24"] # Client address pool
    vpn_client_protocols = ["OpenVPN"]

    # Azure AD Configuration for Authentication
    aad_tenant   = "https://login.microsoftonline.com/${var.AZURE_TENANT_ID}" # Azure AD tenant ID
    aad_issuer   = "https://sts.windows.net/${var.AZURE_TENANT_ID}/" # Azure AD issuer URL
    aad_audience = "41b23e61-6c1e-4545-b367-cd054e0ed4b4" # Azure AD audience
  }
}

My vnet.tf script is below (edited to include the gateway subnet expected by my vpn gateway):

vnet.tf

resource "azurerm_virtual_network" "this" {
  name                = "${local.prefix}-vnet"
  location            = azurerm_resource_group.this.location
  resource_group_name = azurerm_resource_group.this.name
  address_space       = [local.cidr]
  tags                = local.tags
}

resource "azurerm_network_security_group" "this" {
  name                = "${local.prefix}-nsg"
  location            = azurerm_resource_group.this.location
  resource_group_name = azurerm_resource_group.this.name
  tags                = local.tags
}

resource "azurerm_network_security_rule" "aad" {
  name                        = "AllowAAD"
  priority                    = 200
  direction                   = "Outbound"
  access                      = "Allow"
  protocol                    = "Tcp"
  source_port_range           = "*"
  destination_port_range      = "443"
  source_address_prefix       = "VirtualNetwork"
  destination_address_prefix  = "AzureActiveDirectory"
  resource_group_name         = azurerm_resource_group.this.name
  network_security_group_name = azurerm_network_security_group.this.name
}

resource "azurerm_network_security_rule" "azfrontdoor" {
  name                        = "AllowAzureFrontDoor"
  priority                    = 201
  direction                   = "Outbound"
  access                      = "Allow"
  protocol                    = "Tcp"
  source_port_range           = "*"
  destination_port_range      = "443"
  source_address_prefix       = "VirtualNetwork"
  destination_address_prefix  = "AzureFrontDoor.Frontend"
  resource_group_name         = azurerm_resource_group.this.name
  network_security_group_name = azurerm_network_security_group.this.name
}

resource "azurerm_subnet" "public" {
  name                 = "${local.prefix}-public"
  resource_group_name  = azurerm_resource_group.this.name
  virtual_network_name = azurerm_virtual_network.this.name
  address_prefixes     = [cidrsubnet(local.cidr, 3, 0)]

  delegation {
    name = "databricks"
    service_delegation {
      name = "Microsoft.Databricks/workspaces"
      actions = [
        "Microsoft.Network/virtualNetworks/subnets/join/action",
        "Microsoft.Network/virtualNetworks/subnets/prepareNetworkPolicies/action",
      "Microsoft.Network/virtualNetworks/subnets/unprepareNetworkPolicies/action"]
    }
  }
}

resource "azurerm_subnet_network_security_group_association" "public" {
  subnet_id                 = azurerm_subnet.public.id
  network_security_group_id = azurerm_network_security_group.this.id
}

variable "private_subnet_endpoints" {
  default = []
}

resource "azurerm_subnet" "private" {
  name                 = "${local.prefix}-private"
  resource_group_name  = azurerm_resource_group.this.name
  virtual_network_name = azurerm_virtual_network.this.name
  address_prefixes     = [cidrsubnet(local.cidr, 3, 1)]

  enforce_private_link_endpoint_network_policies = true
  enforce_private_link_service_network_policies  = true

  delegation {
    name = "databricks"
    service_delegation {
      name = "Microsoft.Databricks/workspaces"
      actions = [
        "Microsoft.Network/virtualNetworks/subnets/join/action",
        "Microsoft.Network/virtualNetworks/subnets/prepareNetworkPolicies/action",
      "Microsoft.Network/virtualNetworks/subnets/unprepareNetworkPolicies/action"]
    }
  }

  service_endpoints = var.private_subnet_endpoints
}

resource "azurerm_subnet_network_security_group_association" "private" {
  subnet_id                 = azurerm_subnet.private.id
  network_security_group_id = azurerm_network_security_group.this.id
}


resource "azurerm_subnet" "plsubnet" {
  name                                           = "${local.prefix}-privatelink"
  resource_group_name                            = azurerm_resource_group.this.name
  virtual_network_name                           = azurerm_virtual_network.this.name
  address_prefixes                               = [cidrsubnet(local.cidr, 3, 2)]
  enforce_private_link_endpoint_network_policies = true // set to true to disable subnet policy
}


resource "azurerm_virtual_network" "hubvnet" {
  name                = "${local.prefix}-hub-vnet"
  location            = azurerm_resource_group.this.location
  resource_group_name = azurerm_resource_group.this.name
  address_space       = [var.hubcidr]
  tags                = local.tags
}

resource "azurerm_subnet" "hubfw" {
  //name must be fixed as AzureFirewallSubnet
  name                 = "AzureFirewallSubnet"
  resource_group_name  = azurerm_resource_group.this.name
  virtual_network_name = azurerm_virtual_network.hubvnet.name
  address_prefixes     = [cidrsubnet(var.hubcidr, 3, 0)]
}

resource "azurerm_virtual_network_peering" "hubvnet" {
  name                      = "peerhubtospoke"
  resource_group_name       = azurerm_resource_group.this.name
  virtual_network_name      = azurerm_virtual_network.hubvnet.name
  remote_virtual_network_id = azurerm_virtual_network.this.id
  allow_gateway_transit = true
}

resource "azurerm_virtual_network_peering" "spokevnet" {
  name                      = "peerspoketohub"
  resource_group_name       = azurerm_resource_group.this.name
  virtual_network_name      = azurerm_virtual_network.this.name
  remote_virtual_network_id = azurerm_virtual_network.hubvnet.id
  use_remote_gateways = true
}

resource "azurerm_subnet" "hubvpngw" {
  name                 = "GatewaySubnet"
  resource_group_name  = azurerm_resource_group.this.name
  virtual_network_name = azurerm_virtual_network.hubvnet.name
  address_prefixes     = [cidrsubnet(var.hubcidr, 3, 1)] # You can change the subnet range accordingly
}

And my firewall.tf updates as well:

firweall.tf

resource "azurerm_public_ip" "fwpublicip" {
  name                = "hubfirewallpublicip"
  location            = azurerm_resource_group.this.location
  resource_group_name = azurerm_resource_group.this.name
  allocation_method   = "Static"
  sku                 = "Standard"
}

resource "azurerm_firewall" "hubfw" {
  name                = "hubfirewall"
  location            = azurerm_resource_group.this.location
  resource_group_name = azurerm_resource_group.this.name
  sku_name            = "AZFW_VNet"
  sku_tier            = "Standard"

  ip_configuration {
    name                 = "configuration"
    subnet_id            = azurerm_subnet.hubfw.id
    public_ip_address_id = azurerm_public_ip.fwpublicip.id
  }
}

resource "azurerm_firewall_network_rule_collection" "adbfnetwork" {
  name                = "adbcontrolplanenetwork"
  azure_firewall_name = azurerm_firewall.hubfw.name
  resource_group_name = azurerm_resource_group.this.name
  priority            = 200
  action              = "Allow"

  rule {
    name = "databricks-metastore"

    source_addresses = [
      join(", ", azurerm_subnet.public.address_prefixes),
      join(", ", azurerm_subnet.private.address_prefixes),
    ]

    destination_ports = ["3306"]
    destination_addresses = [var.metastoreip]
    protocols = ["TCP"]
  }
}

resource "azurerm_firewall_application_rule_collection" "adbfqdn" {
  name                = "adbcontrolplanefqdn"
  azure_firewall_name = azurerm_firewall.hubfw.name
  resource_group_name = azurerm_resource_group.this.name
  priority            = 200
  action              = "Allow"

  rule {
    name = "databricks-control-plane-services"

    source_addresses = [
      join(", ", azurerm_subnet.public.address_prefixes),
      join(", ", azurerm_subnet.private.address_prefixes),
    ]

    target_fqdns = concat(var.firewallfqdn, ["*.azuredatabricks.net"])

    protocol {
      port = "443"
      type = "Https"
    }
  }
}

resource "azurerm_route_table" "adbroute" {
  name                = "spoke-routetable"
  location            = azurerm_resource_group.this.location
  resource_group_name = azurerm_resource_group.this.name

  route {
    name                   = "to-firewall"
    address_prefix         = "0.0.0.0/0"
    next_hop_type          = "VirtualAppliance"
    next_hop_in_ip_address = azurerm_firewall.hubfw.ip_configuration.0.private_ip_address
  }
}

resource "azurerm_subnet_route_table_association" "publicudr" {
  subnet_id      = azurerm_subnet.public.id
  route_table_id = azurerm_route_table.adbroute.id
}

resource "azurerm_subnet_route_table_association" "privateudr" {
  subnet_id      = azurerm_subnet.private.id
  route_table_id = azurerm_route_table.adbroute.id
}