Elixir Plug to easily add HTTP basic authentication to an app
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This is an Elixir Plug for adding basic authentication into an application.

The plug can be configured to use:

  1. Static username and password in application configuration


  1. Your own custom authentication function

Note that if using option (1), prior to 2.2.1 the library was vulnerable to timing attacks; we suggest updating ~> 2.2.2.

If you are using your own custom authentication function, then you are are on your own. (Plug.Crypto.secure_compare/2 is something that may help you compare binaries in constant time.)

How to use

Add the package as a dependency in your Elixir project using something along the lines of:

  defp deps do
    [{:basic_auth, "~> 2.2.2"}]

Add into the top of a controller, or into a router pipeline a plug declaration like:

plug BasicAuth, use_config: {:your_app, :your_config}

Where :your_app and :your_config should refer to values in your application config.

In your configuration you can set values directly, eg

config :your_app, your_config: [
  username: "admin",
  password: "simple_password",
  realm: "Admin Area"

All configuration is read at runtime to support using REPLACE_OS_VARS as part of a release.

or choose to get one (or all) from environment variables, eg

config :basic_auth, my_auth_with_system: [
  username: {:system, "BASIC_AUTH_USERNAME"},
  password: {:system, "BASIC_AUTH_PASSWORD"},
  realm:    {:system, "BASIC_AUTH_REALM"}

Alternatively you can provide a custom function to the plug to authenticate the user any way you want, such as finding the user from a database.

  plug BasicAuth, callback: &User.find_by_username_and_password/3

(or optionally provide a realm)

  plug BasicAuth, callback: &User.find_by_username_and_password/3, realm: "Area 51"

Where :callback is your custom authentication function that takes a conn, username and a password and returns a conn. Your function must return Plug.Conn.halt(conn) if authentication fails, otherwise you can use Plug.Conn.assign(conn, :current_user, ...) to enhance the conn with variables or session for your controller.

The function must have an arity of 3, and be of the form

@spec myfunction(Plug.Conn.t, String.t, String.t) :: Plug.Conn.t

It will receive a connection, username, and password.

Easy as that!

Authenticating only for specific actions

If you're looking to authenticate only for a subset of actions in a controller you can use plug's when action in syntax as shown below

plug BasicAuth, [use_config: {: your_app, : your_config}] when action in [:edit, :delete]

additionally you can exclude specific actions using not

plug BasicAuth, [use_config: {: your_app, : your_config}] when not action in [:index, :show]

Testing controllers with Basic Auth

If you're storing credentials within configuration files, we can reuse them within our test files directly using snippets like Application.get_env(:basic_auth)[:username].

Update Tests to insert a basic authentication header

Any controller that makes use of basic authentication, will need an additional header injected into the connection in order for your tests to continue to work. The following is a brief snippet of how to get started. There is a more detailed blog post that explains a bit more about what needs to be done.

At the top of my controller test I have something that looks like:

@username Application.get_env(:the_app, :basic_auth)[:username]
@password Application.get_env(:the_app, :basic_auth)[:password]

defp using_basic_auth(conn, username, password) do
  header_content = "Basic " <> Base.encode64("#{username}:#{password}")
  conn |> put_req_header("authorization", header_content)

Then for any tests, I can simply pipe in this helper method to the connection process:

test "GET / successfully renders when basic auth credentials supplied", %{conn: conn} do
  conn = conn
    |> using_basic_auth(@username, @password)
    |> get("/admin/users")

  assert html_response(conn, 200) =~ "Users"

And a test case without basic auth for completeness:

test "GET / without basic auth credentials prevents access", %{conn: conn} do
  conn = conn
    |> get("/admin/users")

  assert response(conn, 401) =~ "401 Unauthorized"