MSAL Node Standalone Sample: Custom INetworkModule Implementation and Network Tracing Via "Fiddler Everywhere"

November 14, 2025 · View on GitHub

This sample demonstrates how to implement a custom INetworkModule that makes it simple for developers to debug network errors and write custom proxy support. There are two ways to run the sample: one is "as-is" in app.ts, the other is via an express server in express.ts. Additionally, instructions are provided on how to use Fiddler Everywhere to perform a network trace of the application.

Fiddler Everywhere is not supported on all operating systems. Fiddler Classic is a free Windows-only version of Fiddler Everywhere. It's important to note that Microsoft Entra ID no longer supports TLS 1.0, which is the default TLS version in Fiddler Classic. The TLS version can be configured via navigating to Tools > Options > HTTPS, then set TLS to 1.2.

Note

This sample is written in TypeScript and was developed with Node version 23.4.0.

Setup

In a terminal, navigate to the directory where package.json resides. Then type:

    npm install

Register

Navigate to the Microsoft Entra admin center and select the Microsoft Entra ID service.
Select the App Registrations blade on the left, then select New registration.
In the Register an application page that appears, enter registration information:
- In the Name section, enter a meaningful application name that will be displayed to users of the app, for example Confidential Client Application.
- Under Supported account types, select Accounts in this organizational directory only.
Select Register to create the application.
In the app's registration screen, find and note the Application (client) ID and Directory (Tenant) ID. These values will be used in the app's configuration file(s) later.
In the app's registration screen, select the Certificates & secrets blade in the left.
- In the Client secrets section, select New client secret.
- Type a key description (for instance app_secret),
- Select one of the available key durations (6 months, 12 months or Custom).
- The generated key value will be displayed when the Add button is selected. Copy and save the generated value for use in later steps.

Before running the sample, the values in the configuration object in app.ts or express.ts will need to be replaced:

const config = {
    auth: {
        clientId: "<ENTER_CLIENT_ID>",
        authority: "https://login.microsoftonline.com/<ENTER_TENANT_ID>",
        clientSecret: "<ENTER_CLIENT_SECRET>",
    },
    ...
};

Implement a custom INetworkModule

There are two approaches to implementing a custom INetworkModule in this sample.

A custom INetworkModule that uses Axios for network requests resides in HttpClientAxios.ts and is imported to app.ts and express.ts. HttpClientAxios.ts can be edited to include console.log()'s to see how network traffic is processed. Axios provides basic proxy functionality. This functionality is used in this sample to enable network tracing in Fiddler Everywhere.
A custom INetworkModule can be implemeted inline in the system configuration. Stubs to mock the default implementation of INetworkModule have been provided.

Use Fiddler Everywhere to perform a network trace

Fiddler acts as a proxy and monitors all traffic on a local network

Download and install Fiddler Everywhere
In HttpClientAxios.ts, uncomment the proxy lines - this tells Axios (and therefore the sample app) to route all traffic through the proxy that Fiddler Everywhere operates on (the port can be configured in the settings of Fiddler Everywhere)

Run the app

Before running the sample (and everytime changes are made to the sample), the TypeScript will need to be compiled. In the same folder, type:

    npx tsc

This will compile the TypeScript into JavaScript, and put the compiled files in the /dist folder.

The sample can now be run by typing:

    node dist/app.js

    node dist/express.js

Two different npm scripts, which will run the above npx and node commands, have been configured in package.json. To compile and start either sample, type:

    npm run start:app

    npm run start:express