Automating Authentication Flows with Docker: Lessons from a Lack of Documentation

In the realm of microservices and scalable infrastructure, Docker has become an indispensable tool. However, when it comes to automating complex auth flows—especially without thorough documentation—the task can rapidly descend into ad hoc solutions that are difficult to maintain. This post explores the approach I took as a senior architect to implement an automated authentication flow using Docker, highlighting pitfalls and best practices.

Understanding the Context

The goal was to streamline the user login process by automating token exchange and session management through containerized services. Due to a lack of formal documentation, I had to reverse engineer existing setups, decipher undocumented scripts, and piece together how the components interacted.

Starting Point: Dissecting the Current Setup

The initial step was to examine all existing containers, scripts, and configuration files. I used commands like:

docker ps -a

to list running containers, and inspected logs and configs to understand their roles. Often, this involved decompiling container images:

docker inspect <container_id>

And analyzing Dockerfiles and entrypoint scripts.

Identifying Key Authentication Components

Typically, auth flows involve these critical components:

• Auth server (OAuth2 / OpenID Connect)
• Token management and refresh logic
• User session handling

Given the undocumented nature, I traced network calls using tools like Wireshark or docker logs outputs to identify API endpoints and token exchanges.

Building a Reproducible Docker Environment

Once components were understood, I developed a Docker Compose setup to simulate the environment:

version: '3'
services:
  auth-server:
    image: auth_server_image
    ports:
      - "8080:80"
  client-app:
    image: client_app_image
    depends_on:
      - auth-server
    environment:
      - AUTH_URL=http://auth-server:8080

This structure allowed consistent testing and further automation.

Automating the Flow

The key was scripting the authentication process. I used a combination of curl commands within containers to emulate login flows:

curl -X POST -d "username=user&password=pass" http://auth-server:8080/auth

and managed token storage with mounted volumes. For automating token refresh, I introduced a cron job inside a dedicated container:

FROM alpine:latest
RUN apk add --no-cache curl bash
COPY refresh_script.sh /refresh_script.sh
CMD ["/bin/bash", "/refresh_script.sh"]

This script periodically fetched new tokens using stored refresh tokens.

Pitfalls and Lessons Learned

1. Documentation Deficit: The biggest challenge was the ambiguity in how containers communicated, which required extensive reverse engineering.
2. Security Risks: Hardcoded credentials in scripts pose security issues; environment variables and secret management should be prioritized.
3. Maintainability: Manual processes can lead to brittle setups; automating with scripts and version-controlled configs is essential.

Final Thoughts

While Docker is a powerful tool for encapsulation, automating auth flows without proper initial documentation demands meticulous investigation and disciplined design. Structuring your containers, scripts, and secrets properly is pivotal. Use logs, network sniffing, and container inspection as your investigative tools, and establish clear documentation moving forward to avoid similar pitfalls.

In future projects, prioritize comprehensive documentation and modular design principles to streamline automation and enhance security. Docker, combined with robust scripting and configuration, can significantly optimize auth flows once you understand the underlying architecture.

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🛠️ QA Tip

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