I have encountered this error on two different code bases in the last few days. After running phx.gen.auth and following the instructions (e.g., mix deps.get and mix ecto.migrate) and running the server, I get the following error
key :current_user not found in: %{conn: %Plug.Conn{adapter: {Plug.Cowboy.Conn, :...}, assigns: %{flash: %{}, ...
Both code bases were fairly small and neither had any form of User or authentication. One code base I ran phx.gen.auth for regular controllers and the other was for LiveView. Both had the above error. Every tutorial and guide I have watched has shown this to “just work”.
The problem seems to lie with the following code snippet in root.html.heex
Do you have the :fetch_current_user plug in place, in your router pipeline somewhere? That’s the plug that puts the current_user in the right place, to be able to pick it up later. The plug is generated and implemented in your MyAppWeb.UserAuth module.
Your @current_user assign can be nil, if there is no logged in user. But you must have the plug in place to at least have the assign available. At least, if you wish to use the root template as modified by phx.gen.auth.
Does it work if you put it in the live.html.heex or app.html.heex layouts? I don’t believe that @current_user works in the root layout and I believe you generally want to keep dynamic stuff out of root. See here.
When I had both dead and liveviews, I used a component for displaying this stuff and called it in each layout.
Maybe you modified the browser pipeline in the router in a way the generator was confused? I’m not sure how that works exactly, but should be easy to find in the phoenix sources. I’d expect a warning when the generator cannot inject the plug (the generators also warn when a file it wants to generate already exists). Good luck with the app!
@linusdm’s answer solved my similar issue. FWIW: if ElixirLS has reformatted the router.ex file, you might find that fetch_current_user cannot get added to router.ex by the generator. In a router.ex with the generated structure, this goes at the end of the “pipeline :browser do” block:
# Inside router.ex
pipeline :browser do
plug(:accepts, ["html"])
plug(:fetch_session)
plug(:fetch_live_flash)
plug(:put_root_layout, html: {LiveViewStudioWeb.Layouts, :root})
plug(:protect_from_forgery)
plug(:put_secure_browser_headers)
plug :fetch_current_user # <--- add this one if missing!
end