Apk-Mitm - A CLI Application That Prepares Android APK Files For HTTPS Inspection

A CLI application that automatically prepares Android APK files for HTTPS inspection

Inspecting a mobile app's HTTPS traffic using a proxy is probably the easiest way to figure out how it works. However, with the Network Security Configuration introduced in Android 7 and app developers trying to prevent MITM attacks using certificate pinning, getting an app to work with an HTTPS proxy has become quite tedious.
apk-mitm automates the entire process. All you have to do is give it an APK file and apk-mitm will:

decode the APK file using Apktool
modify the app's AndroidManifest.xml to make it debuggable
modify the app's Network Security Configuration to allow user-added certificates
insert return-void opcodes to disable certificate pinning logic
encode the patched APK file using Apktool
sign the patched APK file using uber-apk-signer

You can also use apk-mitm to patch apps using Android App Bundle and rooting your phone is not required.

Usage
If you have an up-to-date version of Node.js (8.2+) and Java (8+), you can run this command to patch an app:

$ npx apk-mitm <path-to-apk>

So, if your APK file is called example.apk, you'd run:

$ npx apk-mitm example.apk
 
   ✔ Decoding APK file
   ✔ Modifying app manifest
   ✔ Modifying network security config
   ✔ Disabling certificate pinning
   ✔ Encoding patched APK file
   ✔ Signing patched APK file
 
    Done!  Patched APK: ./example-patched.apk

You can now install the example-patched.apk file on your Android device and use a proxy like Charles or mitmproxy to look at the app's traffic.

Patching App Bundles
You can also patch apps using Android App Bundle with apk-mitm by providing it with a *.xapk file (for example from APKPure) or a *.apks file (which you can export yourself using SAI).

Caveats

If the app uses Google Maps and the map is broken after patching, then the app's API key is probably restricted to the developer's certificate. You'll have to create your own API key without restrictions and replace it in the app's AndroidManifest.xml file.
If apk-mitm crashes while decoding or encoding the issue is probably related to Apktool. Check their issues on GitHub to find possible workarounds. If you happen to find an Apktool version that's not affected by the issue, you can instruct apk-mitm to use it by specifying the path of its JAR file through the --apktool option.

Installation
The above example used npx to download and execute apk-mitm without local installation. If you do want to fully install it, you can do that by running: