azureblob: add --azureblob-disable-instance-discovery

If set this skips requesting Microsoft Entra instance metadata

See #8078

backend/azureblob/azureblob.go

@@ -209,6 +209,22 @@ rclone config file under the ` + "`client_id`, `tenant` and `client_secret`" + `
 keys instead of setting ` + "`service_principal_file`" + `.
 `,
 			Advanced: true,
+		}, {
+			Name: "disable_instance_discovery",
+			Help: `Skip requesting Microsoft Entra instance metadata
+
+This should be set true only by applications authenticating in
+disconnected clouds, or private clouds such as Azure Stack.
+
+It determines whether rclone requests Microsoft Entra instance
+metadata from ` + "`https://login.microsoft.com/`" + ` before
+authenticating.
+
+Setting this to true will skip this request, making you responsible
+for ensuring the configured authority is valid and trustworthy.
+`,
+			Default:  false,
+			Advanced: true,
 		}, {
 			Name: "use_msi",
 			Help: `Use a managed service identity to authenticate (only works in Azure).
@@ -438,6 +454,7 @@ type Options struct {
 	Username                   string               `config:"username"`
 	Password                   string               `config:"password"`
 	ServicePrincipalFile       string               `config:"service_principal_file"`
+	DisableInstanceDiscovery   bool                 `config:"disable_instance_discovery"`
 	UseMSI                     bool                 `config:"use_msi"`
 	MSIObjectID                string               `config:"msi_object_id"`
 	MSIClientID                string               `config:"msi_client_id"`
@@ -726,6 +743,7 @@ func NewFs(ctx context.Context, name, root string, m configmap.Mapper) (fs.Fs, e
 		// Read credentials from the environment
 		options := azidentity.DefaultAzureCredentialOptions{
 			ClientOptions:            policyClientOptions,
+			DisableInstanceDiscovery: opt.DisableInstanceDiscovery,
 		}
 		cred, err = azidentity.NewDefaultAzureCredential(&options)
 		if err != nil {

docs/content/azureblob.md

@@ -180,6 +180,13 @@ If the resource has multiple user-assigned identities you will need to
 unset `env_auth` and set `use_msi` instead. See the [`use_msi`
 section](#use_msi).
 
+If you are operating in disconnected clouds, or private clouds such as
+Azure Stack you may want to set `disable_instance_discovery = true`.
+This determines whether rclone requests Microsoft Entra instance
+metadata from `https://login.microsoft.com/` before authenticating.
+Setting this to `true` will skip this request, making you responsible
+for ensuring the configured authority is valid and trustworthy.
+
 ##### Env Auth: 3. Azure CLI credentials (as used by the az tool)
 
 Credentials created with the `az` tool can be picked up using `env_auth`.