Not-in-the-Middle

⚡ NITM is a microservice that intercepts HTTP/S traffic, powered by Node.js. ⚡

This project is not even close to a stable release. Avoid using it outside the scope of your local environment.

📑 Table of contents

• Requirements
• Configuration
• Certificates
• Setup
  • Node.js
  • Docker
  • Docker Compose
• Usage
  • cURL
  • Chromium
  • System-wide CA setup
• TODO
• Flowchart

🐙 Requirements

• Node.js (required)
• NPM (required)
• openssl (optional, needed only if you have to generate a new CA)

⚙️ Configuration

NITM can be configured through a set of environment variables.

Here is a table that represents all available configuration options.

variable name	default value	description
HTTP_HOST	localhost	public proxy host
HTTP_PORT	8080	public proxy port
HTTPS_HOST	localhost	internal proxy host
HTTPS_PORT	8443	internal proxy port
CA_KEY	.cert/rootCA.key	path to root CA key
CA_CERT	.cert/rootCA.pem	path to root CA cert
CA_PASS	pass	root CA password

More configuration options will be available soon.
Feeling lucky with the default settings? Just proceed to the to certificates section.

If you would like to update the configuration, the easiest way would be to make a new copy of env.example.

cp env.example .env

🔓 Certificates

In order to use NITM, your system or application should be capable of using a custom root CA.

For testing purpose, you can simply rely on the pre-generated keys and forget about all of this.

Otherwise, the name of the generate-root-ca.sh script should be pretty self-explanatory.
It has been used for the freely-distributed certificates under the .cert directory.

🔧 Setup

Node.js

Install the missing dependencies and start the service.

npm install
npm run start

Alternatively, you can start the dev script, which will spawn nodemon process.

npm install
npm run dev

Docker

There is a GitHub workflow that automates the processes of building and publishing the image.
The most recent image build is located at alesandar/nitm:latest. Looking for other another build? Inspect the public tags.

The command below create a new container, based on the latest build.

docker run -e HTTP_HOST=0.0.0.0 -p 127.0.0.1:8080:8080 -t alesandar/nitm:latest`

If you do not want to declare variables one by one, like we did above, just pass an environment file.
In case you did not create an environment file earlier, please go back to the setup section.

docker run --env-file .env -p 127.0.0.1:8080:8080 -t alesandar/nitm`

Docker Compose

Docker Compose makes it even simpler, since most of the configuration is predeclared inside docker-compose.yml.

docker-compose up

For local development, you might want to pass the --build argument (it will build a local image).

docker-compose up --build

🚀 Usage

cURL

There's a simple cURL wrapper, located in .bin/curl.sh, which must take care of all prerequisites.

.bin/curl.sh https://github.com

Alternatively, you can execute the actual cURL binary with the following arguments:

curl --proxy localhost:8080 --cacert .cert/rootCA.pem https://github.com

Chromium

The proxy server can be specified as a command-line argument, but that's not the case with the certificate authority.
Users are required import certificate authorities manually. Follow this steps:

• open Settings and go to Privacy and security Security Manage certificates
• focus the Authorities tab and click on the Import button
• select the Trust this certificate for identifying websites checkbox and hit OK
• navigate to the project's root directory and select the root CA.

As a final step, start the shell script by doing so:

.bin/chromium.sh

Alternative, start Chromium like so:

chromium --proxy-server=localhost:8080

Now open a website of your choice and take a look at the service logs.

System-wide CA setup

The system-wide setup is untested and discouraged. If you want to experiment - do it at your own risk.
Arch Linux users might wish to read the Transport Layer Security/Certificate_authorities.
Anybody else should refer to the documentation of his current operating system.

🐌 TODO

• performance and metrics:
  • implement a monitoring stack in docker-compose.yml (Prometheus, Grafana, ElasticSearch, etc)
  • create a custom Prometheus exporter for exposing request metrics
  • implement a compression algorithm, such as gzip/deflate/
  • implement a caching mechanism
• refactor:
  • rewrite the logic from generate-root-ca.sh inside cert.js and generate root CAs internally
  • create a method that verifies the validity of the root CA
  • follow permanent (301 and 308) and temporary (302, 303, 307) redirects
  • rewrite some of the main methods (e.g. initHTTP and initHTTPS) into a class instances
  • use a method for inline documentation, such as JSDoc
  • consider rewriting the everything in TypeScript
  • decide what type of tagging/versioning system to use for releases
• features and improvements:
  • compile static binaries that will ease the distribution of the service
  • create a CLI module (e.g. ./src/lib/cli.js) for interacting with the service through the command-line
• unit-testing:
  • choose a library (tape?)
  • write performance-oriented tests
  • create a stress-testing environment for high load
• CI/CD:
  • push images to GitHub's registry as well
  • add a workflow for publishing to the NPM registry as well

🔃 Flowchart

Finally, here is a flowchart that illustrates what the service does behind the scenes. It requires a few improvement, but should be more than enough for now.

graph TB

classDef client stroke:#83a598
classDef nitm stroke:#fb4934
classDef dest stroke:#b8bb26

A(web client):::client

B{MITM status}:::nitm
C(root CA):::nitm
D(HTTP proxy):::nitm
E(HTTPS proxy):::nitm

Z(destination):::dest

%% normal flow (MITM is disabled)
A ---|1. request|B ---->|2a. disabled| Z -->|3a. response| A

%% abnormal flow (MITM is enabled)
B ---->|2b. enabled| C
C ---->|3b. trusted| D
D ---->|4b. intercept| E
E ---->|5b. intercept| Z
Z ---->|6b. response| E
E ---->|7b. intercept| D

linkStyle default stroke:#fb4934
linkStyle 0,1 stroke:#83a598
linkStyle 2 stroke:#b8bb26

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