Handle API authentication errors for the Pairing API

- Expand the Fallback controller with some failed
  auth functions
- Add additional error views with useful feedback
  messages
- Add the gen_jwt_token_with_wrong_signature
  function in the JWTTestHelper
- Add the necessary auth tests and adapt existing
  ones

Signed-off-by: Armin Ahmetović <[email protected]>

apps/astarte_pairing_api/lib/astarte_pairing_api_web/controllers/fallback_controller.ex

@@ -61,17 +61,46 @@ defmodule Astarte.Pairing.APIWeb.FallbackController do
     |> render(:"403")
   end
 
-  # This is the final call made by EnsureAuthenticated
-  def auth_error(conn, {:unauthenticated, reason}, _opts) do
-    _ =
-      Logger.info("Refusing unauthenticated request: #{inspect(reason)}.", tag: "unauthenticated")
+  # Invalid authorized path
+  def call(conn, {:error, :invalid_auth_path}) do
+    conn
+    |> put_status(:unauthorized)
+    |> put_view(Astarte.Pairing.APIWeb.ErrorView)
+    |> render(:invalid_auth_path)
+  end
+
+  # This is called when no JWT token is present
+  def auth_error(conn, {:unauthenticated, :unauthenticated}, _opts) do
+    conn
+    |> put_status(:unauthorized)
+    |> put_view(Astarte.Pairing.APIWeb.ErrorView)
+    |> render(:missing_token)
+  end
+
+  # Invalid JWT token
+  def auth_error(conn, {:invalid_token, :invalid_token}, _opts) do
+    conn
+    |> put_status(:unauthorized)
+    |> put_view(Astarte.Pairing.APIWeb.ErrorView)
+    |> render(:invalid_token)
+  end
+
+  # Path not authorized
+  def auth_error(conn, {:unauthorized, :authorization_path_not_matched}, _opts) do
+    conn
+    |> put_status(:forbidden)
+    |> put_view(Astarte.Pairing.APIWeb.ErrorView)
+    |> render(:authorization_path_not_matched, %{method: conn.method, path: conn.request_path})
+  end
 
+  def auth_error(conn, {:unauthenticated, _reason}, _opts) do
     conn
     |> put_status(:unauthorized)
     |> put_view(Astarte.Pairing.APIWeb.ErrorView)
     |> render(:"401")
   end
 
+  # In all other cases, we reply with 403
   def auth_error(conn, _reason, _opts) do
     conn
     |> put_status(:forbidden)

apps/astarte_pairing_api/lib/astarte_pairing_api_web/views/error_view.ex

@@ -31,6 +31,32 @@ defmodule Astarte.Pairing.APIWeb.ErrorView do
     %{errors: %{detail: "Forbidden"}}
   end
 
+  def render("missing_token.json", _assigns) do
+    %{errors: %{detail: "Missing authorization token"}}
+  end
+
+  def render("invalid_token.json", _assigns) do
+    %{errors: %{detail: "Invalid JWT token"}}
+  end
+
+  # TODO: add error message for invalid_token_signature
+
+  def render("invalid_auth_path.json", _assigns) do
+    %{
+      errors: %{
+        detail: "Authorization failed due to an invalid path"
+      }
+    }
+  end
+
+  def render("authorization_path_not_matched.json", %{method: method, path: path}) do
+    %{
+      errors: %{
+        detail: "Unauthorized access to #{method} #{path}. Please verify your permissions"
+      }
+    }
+  end
+
   def render("404.json", _assigns) do
     %{errors: %{detail: "Page not found"}}
   end

apps/astarte_pairing_api/test/astarte_pairing_api_web/auth/auth_test.exs

@@ -45,6 +45,11 @@ defmodule Astarte.Pairing.APIWeb.AuthTest do
       {:ok, conn: conn}
     end
 
+    test "no token returns 401", %{conn: conn} do
+      conn = post(conn, agent_path(conn, :create, @realm), data: @create_attrs)
+      assert json_response(conn, 401)["errors"]["detail"] == "Missing authorization token"
+    end
+
     test "succeeds with specific authorizations", %{conn: conn} do
       register_authorizations = ["POST::agent/devices"]
 
@@ -86,7 +91,8 @@ defmodule Astarte.Pairing.APIWeb.AuthTest do
         |> authorize_conn(register_authorizations)
         |> post(agent_path(conn, :create, @realm), data: @create_attrs)
 
-      assert json_response(conn, 403)["errors"]["detail"] == "Forbidden"
+      assert json_response(conn, 403)["errors"]["detail"] ==
+               "Unauthorized access to #{conn.assigns.method} #{conn.assigns.path}. Please verify your permissions"
     end
 
     test "fails with authorization for different method", %{conn: conn} do
@@ -97,7 +103,30 @@ defmodule Astarte.Pairing.APIWeb.AuthTest do
         |> authorize_conn(register_authorizations)
         |> post(agent_path(conn, :create, @realm), data: @create_attrs)
 
-      assert json_response(conn, 403)["errors"]["detail"] == "Forbidden"
+      assert json_response(conn, 403)["errors"]["detail"] ==
+               "Unauthorized access to #{conn.assigns.method} #{conn.assigns.path}. Please verify your permissions"
+    end
+
+    test "invalid JWT token returns 401", %{conn: conn} do
+      conn =
+        put_req_header(
+          conn,
+          "authorization",
+          "bearer invalid_token"
+        )
+        |> post(agent_path(conn, :create, @realm), data: @create_attrs)
+
+      assert json_response(conn, 401)["errors"]["detail"] == "Invalid JWT token"
+    end
+
+    test "token with mismatched signature returns 401", %{conn: conn} do
+      token = JWTTestHelper.gen_jwt_token_with_wrong_signature(["^POST$::agent/devices"])
+
+      conn =
+        put_req_header(conn, "authorization", "bearer #{token}")
+        |> post(agent_path(conn, :create, @realm), data: @create_attrs)
+
+      assert json_response(conn, 401)["errors"]["detail"] == "Invalid JWT token"
     end
   end
 

apps/astarte_pairing_api/test/support/jwt_test_helper.ex

@@ -40,6 +40,16 @@ defmodule Astarte.Pairing.APIWeb.JWTTestHelper do
     jwt
   end
 
+  def gen_jwt_token_with_wrong_signature(authorization_paths) do
+    valid_token = gen_jwt_token(authorization_paths)
+
+    [header, payload, _signature] = String.split(valid_token, ".")
+
+    fake_signature = "fake_signature"
+
+    "#{header}.#{payload}.#{fake_signature}"
+  end
+
   def gen_jwt_all_access_token do
     gen_jwt_token([".*::.*"])
   end