Login and Sessions

Goal

This snapshot advances Solstice Ledger by teaching you to authenticate with signed session cookies.

Every numbered folder is a complete app. Run this stage independently, then compare it with the previous folder.

Prerequisites

Use Elixir 1.15+, Mix, and Docker for Postgres stages.

Port 4001 must be free. Copy .env.example before starting database stages.

• Elixir and Mix
• A code editor and terminal
• Docker from part 4 onward

Concepts

Plug.Session stores an opaque cookie. Keep only the user id in the session.

Keep controllers thin: plugs prepare requests, contexts enforce rules, and HEEx escapes output by default.

Walkthrough

Verify email/password, put_session user_id, clear on logout.

Read the example, then open the matching snapshot. The repository includes the surrounding setup and error handling.

conn |> put_session(:user_id, user.id) |> redirect(to: ~p"/")

Run and verify

Enter 07-Login-And-Sessions, fetch deps, copy .env.example, and start Phoenix on port 4001.

Open http://127.0.0.1:4001. Watch the terminal for validation and database errors.

docker compose up -d
git clone https://github.com/michaeldunga1/fcc-phoenix-blog.git
cd fcc-phoenix-blog/07-Login-And-Sessions
mix deps.get
cp .env.example .env
mix phx.server

Troubleshooting

Changing SECRET_KEY_BASE invalidates cookies.

For database failures, confirm Docker and the solstice_NN name when applicable. Never commit .env or _build/deps secrets.

• Read the first error first
• Restart after environment changes
• Never commit secrets

Try this

Log in, restart, confirm session, then log out.

Test a happy path and one invalid or unauthorized request.

• Make one small change
• Test it in the browser
• Compare with the next snapshot only after it works