Assign isn't assigning?

I have a piece of code that gets executed on successful user signin, and everything seems to work fine, except that one of my assigned variables isn’t getting assigned by the code, but it works fine when I do it while debugging with pry…

Here is my code:

case TokenAuthentication.verify_token_value(token) do
  {:ok, user} ->
    |> put_session(:user_id,
    |> configure_session(renew: true)
    |> put_flash(:info, "Congratulations, #{user.first_name}, you were signed in successfully.")
    |> assign(:current_user, user)
    |> redirect(to: page_path(conn, :index))

and when I pry I have

assigns: %{current_user: nil}

but then I do assign(conn, :current_user, user) at the prompt and I get

assigns: %{current_user: %Myapp.User{__meta__: #Ecto.Schema.Metadata<:loaded, "users">,
    auth_tokens: #Ecto.Association.NotLoaded<association :auth_tokens is not loaded>,
    email: "", first_name: "Test", id: 20,
    inserted_at: ~N[2017-05-09 13:06:32.374191], last_name: "McTest",
    password: nil, password_confirmation: nil,
    password_hash: "$2b$12$v8zTVSz0TGJ6COKlGb0TY.pbg3lnpJMZprmjDz3OS6s5aZWIDgsaC",
    updated_at: ~N[2017-05-09 13:06:32.374206]}}

as expected. I know that Elixir shouldn’t have side effects, so how is my running it at the prompt different?

Your code isn’t quite doing what you think it is. Here it is formatted better:

    |> put_session(:user_id,
    |> configure_session(renew: true)
    |> put_flash(:info, "Congratulations, #{user.first_name}, you were signed in successfully.")
    |> assign(:current_user, user)
    # everything prior to this line has now been thrown away, you didn't bind it to anything

    |> redirect(to: page_path(conn, :index))

If I had to guess IEx.pry will return whatever it is you’ve last written in it. So if you assign a conn, that assigned conn will get passed through to the redirect function.


Remember that all data structures in Elixir are immutable, so is a %Plug.Conn{}.

Plug.Conn.assign/3 always returns a new %Plug.Conn{}. So your code should be

conn = conn
       |> put_session(:user_id,
       |> configure_session(renew: true)
       |> put_flash(:info, "Congratulations, #{user.first_name}, you were signed in successfully.")
       |> assign(:current_user, user)


redirect(conn, to: page_path(conn, :index))

Note that the local variable conn is reassigned.

1 Like

Exactly right, thank you, I think I should have seen that.

If you don’t mind indulging me a little further, the reason I am debugging this is that the current_user never makes it to my template. Here’s my authentication scheme:

(1) User signs up, generate a jwt using Guardian.encode_and_sign, send a verification email to the new user with a link containing the token

(2) User clicks the link, the jwt is checked by Guardian.decode_and_verify, then that code above is executed

Now that I think about it, the problem seems to be that the redirect sends the connection back through the router where it hits my pipeline, which resets current_user anyway:

pipeline :browser_session do
  plug Guardian.Plug.VerifySession
  plug Guardian.Plug.LoadResource
  plug Myapp.CurrentUser # gets current_user using Guardian.Plug.current_resource

But I’m guessing that this is the problem, somehow the non-Plug functionality of Guardian and the Plug stuff don’t work together. I don’t suppose anyone knows off-hand how these pieces of Guardian should work together, i.e. should I somehow be doing a Guardian.Plug.sign_in for the user once their link is verified? I am a little worried that the token from the email verification process is still floating around out there and might muck up the works.

I’m not familiar with Guardian so excuse me if I’m wrong.

Since you’re using token authentication, the token should be maintained by the client side code (e.g. javascript on the browser side). The client should carry the token on every request whenever the token is available.

However, redirect is a two-step action:

  1. the browser receives a response with status code 302 and a Location header, which contains a URL.
  2. the browser sends another GET request immediately to the URL in Location header.

Unfortunately, you can’t control the second step. You can’t add headers to it, you can’t specify the HTTP method, you can’t add cookie to it, and you can’t attach token to it. I think this is the reason why you lose the current_user after redirect.

If you are building a single-page application, try not to use redirect. Let Javascript handle page switching.

1 Like

Thanks, that was part of the problem. I was also right that I needed to use Guardian to sign in after verifying the emailed token-link. I should probably put together a little article detailing the process of setting up passwordless authentication using the Guardian library since everything I’ve seen so far uses Phoenix.Token, which doesn’t have a very thorough set of functions.

Guardian is useful if you need JWT. If you are just using it as a token you really should be using Phoenix.Token. And the reason Phoenix does not include little pipeline helpers for it is that they are so simple to write that most just write them straight in their router to call in their pipeline.

If however you want a set of pre-made ones I know there are a couple up on :slight_smile:

Thanks! I’m super new to this so I only barely know what I’m doing, just sort of having fun learning. Is there somewhere to learn how to do that? I also have an API that is in Guardian, which is why I used it here too, maybe I should drop it altogether?

Ehh, depends. If it is already in production, no, no point breaking existing things. If it is not but you are using some of the JWT specific features or plan to, then keep guardian, and use it everywhere to keep things ‘uniform’. If you just need a token everywhere with no special JWT stuff then use phoenix tokens everywhere. :slight_smile:

Lots of docs all over google (this is not really phoenix specific) but I do not have any ready on hand. ^.^;

Lol yea it’ll be a while before I’m worrying about production. This is the first time I’m learning how to make apps in any language, I just chose Elixir/Phoenix because it sounded fun (and I have a math background, there is something that feels math here…). I’ve noticed that if you don’t already have a background in Rails or Node, etc, that learning materials can be a little tough to come by. But it’s all good, fun all the same.

I came from the erlang world instead of the rails/node world, the concepts clicked, but wow it has a weird structure to me, it still does. ^.^