ash_authentication

# SPDX-FileCopyrightText: 2026 Alembic Pty Ltd
#
# SPDX-License-Identifier: MIT

if Code.ensure_loaded?(Wax.Challenge) do
  defmodule AshAuthentication.Strategy.WebAuthn.Plug do
    @moduledoc """
    Plug handlers for the WebAuthn strategy.

    Handles registration challenges, registration, authentication challenges,
    and authentication via HTTP requests. Challenges are stored in the Plug session.
    """

    alias AshAuthentication.{Errors.AuthenticationFailed, Info, Strategy, Strategy.WebAuthn}
    alias Plug.Conn
    import Ash.PlugHelpers, only: [get_actor: 1, get_tenant: 1, get_context: 1]
    import AshAuthentication.Plug.Helpers, only: [store_authentication_result: 2]
    import Ash.Expr, only: [ref: 1]
    require Ash.Query
    require Logger

    @session_key "webauthn_challenge"

    @doc "Generate and return a registration challenge."
    @spec registration_challenge(Conn.t(), WebAuthn.t()) :: Conn.t()
    def registration_challenge(conn, strategy) do
      tenant = get_tenant(conn)
      {:ok, challenge} = WebAuthn.Actions.registration_challenge(strategy, tenant)

      rp_id = WebAuthn.Helpers.resolve_rp_id(strategy, tenant)
      rp_name = WebAuthn.Helpers.resolve_rp_name(strategy, tenant)

      response = %{
        challenge: Base.url_encode64(challenge.bytes, padding: false),
        rp: %{id: rp_id, name: rp_name},
        authenticatorSelection: %{
          authenticatorAttachment: strategy.authenticator_attachment,
          userVerification: strategy.user_verification,
          residentKey: strategy.resident_key
        },
        attestation: strategy.attestation,
        timeout: strategy.timeout
      }

      # Store challenge as serializable map (not struct) for cookie session stores
      challenge_data = %{
        bytes: Base.encode64(challenge.bytes),
        type: challenge.type,
        origin: challenge.origin,
        rp_id: challenge.rp_id,
        issued_at: challenge.issued_at
      }

      conn
      |> Conn.put_session(@session_key, challenge_data)
      |> Conn.put_resp_content_type("application/json")
      |> Conn.send_resp(200, Jason.encode!(response))
    end

    @doc "Handle a registration request."
    @spec register(Conn.t(), WebAuthn.t()) :: Conn.t()
    def register(conn, strategy) do
      case reconstruct_challenge(conn, :attestation, strategy) do
        nil ->
          conn
          |> Conn.delete_session(@session_key)
          |> store_authentication_result(missing_challenge_error(strategy, :register))

        challenge ->
          conn = Conn.delete_session(conn, @session_key)
          params = subject_params(conn, strategy)
          opts = opts(conn) ++ [challenge: challenge]
          result = Strategy.action(strategy, :register, params, opts)
          store_authentication_result(conn, result)
      end
    end

    @doc "Generate and return an authentication challenge."
    @spec authentication_challenge(Conn.t(), WebAuthn.t()) :: Conn.t()
    def authentication_challenge(conn, strategy) do
      tenant = get_tenant(conn)
      params = conn.params
      identity_value = params[to_string(strategy.identity_field)]

      # FIXED: Look up credentials for a SPECIFIC user, not all credentials
      allow_credentials =
        if identity_value do
          lookup_user_credentials(strategy, identity_value, tenant)
        else
          # Discoverable credential flow (passkeys) - no allow_credentials needed
          []
        end

      {:ok, challenge} =
        WebAuthn.Actions.authentication_challenge(strategy, allow_credentials, tenant)

      response = %{
        challenge: Base.url_encode64(challenge.bytes, padding: false),
        rpId: WebAuthn.Helpers.resolve_rp_id(strategy, tenant),
        userVerification: strategy.user_verification,
        timeout: strategy.timeout,
        allowCredentials:
          Enum.map(allow_credentials, fn {cred_id, _key} ->
            %{id: Base.url_encode64(cred_id, padding: false), type: "public-key"}
          end)
      }

      # Store challenge as serializable map
      challenge_data = %{
        bytes: Base.encode64(challenge.bytes),
        type: challenge.type,
        origin: challenge.origin,
        rp_id: challenge.rp_id,
        allow_credentials:
          Enum.map(allow_credentials, fn {cred_id, cose_key} ->
            {Base.encode64(cred_id), cose_key}
          end),
        issued_at: challenge.issued_at
      }

      conn
      |> Conn.put_session(@session_key, challenge_data)
      |> Conn.put_resp_content_type("application/json")
      |> Conn.send_resp(200, Jason.encode!(response))
    end

    @doc "Handle an authentication request."
    @spec sign_in(Conn.t(), WebAuthn.t()) :: Conn.t()
    def sign_in(conn, strategy) do
      case reconstruct_challenge(conn, :authentication, strategy) do
        nil ->
          conn
          |> Conn.delete_session(@session_key)
          |> store_authentication_result(missing_challenge_error(strategy, :sign_in))

        challenge ->
          conn = Conn.delete_session(conn, @session_key)
          params = subject_params(conn, strategy)
          opts = opts(conn) ++ [challenge: challenge]
          result = Strategy.action(strategy, :sign_in, params, opts)
          store_authentication_result(conn, result)
      end
    end

    @doc """
    Generate and return a registration challenge for adding a credential to the
    current user.

    Requires an authenticated actor on the connection.
    """
    @spec add_credential_challenge(Conn.t(), WebAuthn.t()) :: Conn.t()
    def add_credential_challenge(conn, strategy) do
      case get_actor(conn) do
        nil ->
          store_authentication_result(conn, unauthenticated_error(strategy, :add_credential))

        _actor ->
          registration_challenge(conn, strategy)
      end
    end

    @doc """
    Handle an `add_credential` request — attach a new credential to the
    authenticated user.

    Requires an authenticated actor on the connection.
    """
    @spec add_credential(Conn.t(), WebAuthn.t()) :: Conn.t()
    def add_credential(conn, strategy) do
      with actor when not is_nil(actor) <- get_actor(conn),
           %Wax.Challenge{} = challenge <- reconstruct_challenge(conn, :attestation, strategy) do
        conn = Conn.delete_session(conn, @session_key)
        params = subject_params(conn, strategy)
        opts = opts(conn) ++ [challenge: challenge, user: actor]
        result = WebAuthn.Actions.add_credential(strategy, params, opts)
        store_authentication_result(conn, result)
      else
        nil ->
          store_authentication_result(conn, unauthenticated_error(strategy, :add_credential))

        _ ->
          conn
          |> Conn.delete_session(@session_key)
          |> store_authentication_result(missing_challenge_error(strategy, :add_credential))
      end
    end

    defp unauthenticated_error(strategy, action) do
      {:error,
       AuthenticationFailed.exception(
         strategy: strategy,
         caused_by: %{
           module: __MODULE__,
           strategy: strategy,
           action: action,
           message: "An authenticated user is required to add a credential"
         }
       )}
    end

    defp missing_challenge_error(strategy, action) do
      {:error,
       AuthenticationFailed.exception(
         strategy: strategy,
         caused_by: %{
           module: __MODULE__,
           strategy: strategy,
           action: action,
           message: "Missing or invalid WebAuthn challenge in session"
         }
       )}
    end

    # Reconstruct a Wax.Challenge from the serialized session data.
    # We store challenges as plain maps because cookie session stores
    # cannot serialize arbitrary Elixir structs.
    defp reconstruct_challenge(conn, type, strategy) do
      with %{} = data <- Conn.get_session(conn, @session_key),
           {:ok, bytes} <- Base.decode64(data["bytes"] || data[:bytes]) do
        build_challenge(data, bytes, type, strategy)
      else
        _ -> nil
      end
    end

    defp build_challenge(data, bytes, type, strategy) do
      base = %Wax.Challenge{
        type: type,
        bytes: bytes,
        origin: data["origin"] || data[:origin],
        rp_id: data["rp_id"] || data[:rp_id],
        issued_at: data["issued_at"] || data[:issued_at],
        origin_verify_fun: {Wax, :origins_match?, []}
      }

      case type do
        :attestation ->
          %{
            base
            | attestation: strategy.attestation,
              trusted_attestation_types: [:none, :basic, :self, :uncertain],
              verify_trust_root: false
          }

        _ ->
          %{base | allow_credentials: decode_allow_credentials(data)}
      end
    end

    defp decode_allow_credentials(data) do
      (data["allow_credentials"] || data[:allow_credentials] || [])
      |> Enum.flat_map(fn {encoded_id, cose_key} ->
        case Base.decode64(encoded_id) do
          {:ok, decoded_id} -> [{decoded_id, cose_key}]
          :error -> []
        end
      end)
    end

    defp subject_params(conn, strategy) do
      subject_name =
        strategy.resource
        |> Info.authentication_subject_name!()
        |> to_string()

      Map.get(conn.params, subject_name, %{})
    end

    defp opts(conn) do
      [actor: get_actor(conn), tenant: get_tenant(conn), context: get_context(conn)]
      |> Enum.reject(&is_nil(elem(&1, 1)))
    end

    # FIXED: Look up credentials for a SPECIFIC user by identity field.
    # The original version read ALL credentials for ALL users.
    defp lookup_user_credentials(strategy, identity_value, tenant) do
      context = %{private: %{ash_authentication?: true}}
      ash_opts = [authorize?: false]
      ash_opts = if tenant, do: Keyword.put(ash_opts, :tenant, tenant), else: ash_opts

      identity_field = strategy.identity_field

      # First find the user by identity
      with {:ok, user} when not is_nil(user) <-
             strategy.resource
             |> Ash.Query.new()
             |> Ash.Query.set_context(context)
             |> Ash.Query.filter(^ref(identity_field) == ^identity_value)
             |> Ash.Query.for_read(:read, %{}, ash_opts)
             |> Ash.read_one(),
           # Then load their credentials via the relationship
           {:ok, user} <-
             Ash.load(user, [strategy.credentials_relationship_name], ash_opts) do
        user
        |> Map.get(strategy.credentials_relationship_name, [])
        |> Enum.map(fn cred ->
          {Map.get(cred, strategy.credential_id_field), Map.get(cred, strategy.public_key_field)}
        end)
      else
        _ -> []
      end
    rescue
      error in [
        Ash.Error.Invalid,
        Ash.Error.Forbidden,
        Ash.Error.Framework,
        Ash.Error.Unknown
      ] ->
        Logger.warning("WebAuthn credential lookup failed: #{Exception.message(error)}")
        []
    end
  end
else
  defmodule AshAuthentication.Strategy.WebAuthn.Plug do
    @moduledoc """
    Plug handlers for the WebAuthn strategy.

    The WebAuthn plug requires the optional `:wax_` dependency.
    """

    alias AshAuthentication.Errors.AuthenticationFailed
    import AshAuthentication.Plug.Helpers, only: [store_authentication_result: 2]

    def registration_challenge(conn, strategy),
      do: missing_wax_dependency(conn, strategy, :registration_challenge)

    def register(conn, strategy),
      do: missing_wax_dependency(conn, strategy, :register)

    def authentication_challenge(conn, strategy),
      do: missing_wax_dependency(conn, strategy, :authentication_challenge)

    def sign_in(conn, strategy),
      do: missing_wax_dependency(conn, strategy, :sign_in)

    def add_credential_challenge(conn, strategy),
      do: missing_wax_dependency(conn, strategy, :add_credential_challenge)

    def add_credential(conn, strategy),
      do: missing_wax_dependency(conn, strategy, :add_credential)

    defp missing_wax_dependency(conn, strategy, action) do
      store_authentication_result(
        conn,
        {:error,
         AuthenticationFailed.exception(
           strategy: strategy,
           caused_by: %{
             module: __MODULE__,
             strategy: strategy,
             action: action,
             message: "The WebAuthn strategy requires the optional `:wax_` dependency"
           }
         )}
      )
    end
  end
end