COOP-270: Porting code from original repo

Ported code from uk-pcw and fixed `mix check` issues.

.doctor.exs

@@ -0,0 +1,3 @@
+%Doctor.Config{
+  ignore_paths: [~r/test\/support/],
+}

README.md

@@ -1,11 +1,19 @@
 # CloudflareAccessEx
 
-**TODO: Add description**
+## TODO
+
+- [ ] Add a test `JwksStrategy`
+- [ ] If the keys get rotated unexpectedly, the 'JwksStrategy` signers will be out of date until the next poll.
+- [ ] As the `JwksStrategy` module will be called for every request, it is a potential bottleneck.
+      Should consider using an ets table or other shared memory mechanism.
+- [ ] Create a `Plug` module.
+- [ ] Write a better Readme
+- [ ] Consider publishing to hex
+- [ ] Consider contributing `JwksStrategy` (if good) back to [joken_jwks](https://github.com/joken-elixir/joken_jwks)
 
 ## Installation
 
-If [available in Hex](https://hex.pm/docs/publish), the package can be installed
-by adding `cloudflare_access_ex` to your list of dependencies in `mix.exs`:
+For now, installations should be through git reference. Tags will be available for releases.
 
 ```elixir
 def deps do

lib/cloudflare_access_ex.ex

@@ -2,15 +2,13 @@ defmodule CloudflareAccessEx do
   @moduledoc """
     This library aims to simplify the process of sitting an application behind Cloudflare Access.
 
-    By default, this library starts an Application (see `CloudflareAccessEx.Application`).
-    The application will read Application config to determine which Cloudflare Access domains to
-    retrieve JWKs from. These keys can then be used to verify the application tokens sent by Cloudflare Access
-    when your application is accessed.
+    By default, this library starts its own supervision tree. The root application will read Application
+    config to determine which Cloudflare Access domains to retrieve JWKs from. These keys can then be used
+    to verify the application tokens sent by Cloudflare Access when your application is accessed.
 
     The [Cloudflare docs](https://developers.cloudflare.com/cloudflare-one/identity/authorization-cookie/application-token/)
     provide more information.
 
-    TODO:
     The library also provides a Plug (see `CloudflareAccessEx.Plug`) that can be used to to extract and
     verify tokens from requests.
 

lib/cloudflare_access_ex/access_token_verifier.ex

@@ -0,0 +1,200 @@
+defmodule CloudflareAccessEx.AccessTokenVerifier do
+  @moduledoc """
+    Verifies a Cloudflare Access token (JWT) and returns decoded information from the token.
+  """
+
+  require Logger
+  alias CloudflareAccessEx.{Config, JwksStrategy}
+
+  @opaque t :: %__MODULE__{
+            domain: String.t(),
+            audience: String.t(),
+            issuer: String.t(),
+            jwks_strategy: atom()
+          }
+
+  @enforce_keys [:domain, :audience, :issuer, :jwks_strategy]
+  defstruct [:domain, :audience, :issuer, :jwks_strategy]
+
+  @type verified_token() ::
+          :anonymous
+          | {:user,
+             %{
+               required(id: String.t()) => String.t(),
+               required(email: String.t()) => String.t()
+             }}
+  @type verify_result() :: {:ok, verified_token()} | {:error, atom() | Keyword.t()}
+
+  @doc """
+  Creates an AccessTokenVerifier that can be used by `AccessTokenVerifier.verify/2`.
+
+  If the config is an atom, it will be used to lookup the config in the `:cloudflare_access_ex` `Application` environment.
+
+  Alternatively, the config can be a keyword list with the following keys:
+
+  * `:domain` - The domain to verify the token against. This can be a string or an atom that is used to lookup the domain in the `:cloudflare_access_ex` `Application` environment.
+  * `:audience` - The audience to verify the token against.
+  * `:jwks_strategy` - The module to use to fetch the public keys from Cloudflare's JWKS endpoint. Defaults to `CloudflareAccessEx.JwksStrategy`.
+
+  ## Examples
+
+      iex> Application.put_env(:cloudflare_access_ex, :my_cfa_app, [
+      ...>   domain: "example.com",
+      ...>   audience: "audience_string",
+      ...> ])
+      ...>
+      ...> AccessTokenVerifier.create(:my_cfa_app)
+      %AccessTokenVerifier{
+        audience: "audience_string",
+        domain: "example.com",
+        issuer: "https://example.com",
+        jwks_strategy: CloudflareAccessEx.JwksStrategy
+      }
+
+      iex> Application.put_env(:cloudflare_access_ex, :my_cfa_app, [
+      ...>   domain: :example,
+      ...>   audience: "audience_string",
+      ...> ])
+      ...> Application.put_env(:cloudflare_access_ex, :example,
+      ...>   domain: "example.com"
+      ...> )
+      ...>
+      ...> AccessTokenVerifier.create(:my_cfa_app)
+      %AccessTokenVerifier{
+        audience: "audience_string",
+        domain: "example.com",
+        issuer: "https://example.com",
+        jwks_strategy: CloudflareAccessEx.JwksStrategy
+      }
+
+      iex> AccessTokenVerifier.create(
+      ...>   domain: "example.com",
+      ...>   audience: "audience_string",
+      ...>   jwks_strategy: MyCustomJwksStrategy
+      ...> )
+      %AccessTokenVerifier{
+        audience: "audience_string",
+        domain: "example.com",
+        issuer: "https://example.com",
+        jwks_strategy: MyCustomJwksStrategy
+      }
+  """
+  @spec create(atom | keyword) :: __MODULE__.t()
+  def create(config_key) when is_atom(config_key) do
+    opts =
+      Application.get_env(:cloudflare_access_ex, config_key) ||
+        throw("Could not find config for #{inspect(config_key)} in :cloudflare_access_ex")
+
+    create(opts)
+  end
+
+  def create(opts) when is_list(opts) do
+    audience =
+      Keyword.get(opts, :audience) ||
+        throw(":audience is required in cloudflare_access_ex config")
+
+    domain =
+      Keyword.get(opts, :domain) || throw(":domain is required in cloudflare_access_ex config")
+
+    jwks_strategy = Keyword.get(opts, :jwks_strategy) || JwksStrategy
+
+    domain = Config.resolve_domain(domain)
+    issuer = Config.get_issuer(domain)
+
+    %__MODULE__{
+      domain: domain,
+      issuer: issuer,
+      audience: audience,
+      jwks_strategy: jwks_strategy
+    }
+  end
+
+  @doc """
+  Verifies the authenticity of the Cloudflare Access token in the given `Plug.Conn` or access_token against the given verifier.
+  """
+  @spec verify(Plug.Conn.t() | binary(), __MODULE__.t()) ::
+          verify_result()
+  def verify(conn = %Plug.Conn{}, config) do
+    header = Plug.Conn.get_req_header(conn, "cf-access-jwt-assertion")
+
+    case header do
+      [cf_access_token] -> verify(cf_access_token, config)
+      [] -> {:error, :header_not_found}
+      _ -> {:error, :multiple_headers_found}
+    end
+  end
+
+  def verify(access_token, verifier) do
+    joken_result =
+      Joken.verify_and_validate(
+        token_config(),
+        access_token,
+        nil,
+        verifier,
+        hooks(verifier)
+      )
+
+    joken_result |> to_verify_result()
+  end
+
+  defp to_verify_result(joken_result) do
+    case joken_result do
+      {:ok, claims = %{"sub" => ""}} ->
+        Logger.debug("Cloudflare Access token is anonymous: #{log_inspect(claims)}")
+        {:ok, :anonymous}
+
+      {:ok, claims = %{"sub" => sub, "email" => email}} when email != "" ->
+        user = {:user, %{id: sub, email: email}}
+        Logger.debug("Cloudflare Access token is for user #{log_inspect(claims)}")
+        {:ok, user}
+
+      {:ok, claims} ->
+        Logger.warning(
+          "Cloudflare Access token did not have expected claims #{log_inspect(claims)}"
+        )
+
+        {:error, [message: "Invalid token", claims: claims]}
+
+      error ->
+        Logger.warning("Cloudflare Access error #{inspect(error)}")
+        error
+    end
+  end
+
+  defp token_config() do
+    Joken.Config.default_claims(skip: [:jti, :iss, :aud])
+    # Default audience claim does not verify against an array of audiences
+    |> Joken.Config.add_claim("aud", nil, &verify_audience/3)
+    |> Joken.Config.add_claim("iss", nil, &verify_issuer/3)
+  end
+
+  defp verify_audience(aud, _claims, %{audience: expected}) when is_list(aud),
+    do: expected in aud
+
+  defp verify_audience(aud, _claims, %{audience: expected})
+       when is_binary(expected) and expected != "",
+       do: expected == aud
+
+  defp verify_audience(_, _, verifier),
+    do: throw("Expected audience not provided on verifier: #{inspect(verifier)}")
+
+  defp verify_issuer(iss, _claims, %{issuer: expected})
+       when is_binary(expected) and expected != "",
+       do: expected == iss
+
+  defp verify_issuer(_, _, verifier),
+    do: throw("Expected issuer not provided on verifier: #{inspect(verifier)}")
+
+  defp hooks(verifier) do
+    [
+      {
+        JokenJwks,
+        strategy: verifier.jwks_strategy, domain: verifier.domain
+      }
+    ]
+  end
+
+  defp log_inspect(claims) do
+    inspect(claims |> Map.delete("identity_nonce"))
+  end
+end

lib/cloudflare_access_ex/application.ex

@@ -1,16 +1,21 @@
 defmodule CloudflareAccessEx.Application do
-  # See https://hexdocs.pm/elixir/Application.html
-  # for more information on OTP Applications
   @moduledoc false
-
   use Application
 
+  alias CloudflareAccessEx.{Config, JwksStrategy}
+
   @impl true
-  def start(_type, _args) do
-    children = [
-      # Starts a worker by calling: CloudflareAccessEx.Worker.start_link(arg)
-      # {CloudflareAccessEx.Worker, arg}
-    ]
+  def start(_type, args) do
+    domains =
+      Keyword.get(args, :domains) ||
+        Config.get_domain_strings() ||
+        []
+
+    children =
+      domains
+      |> Enum.map(fn domain ->
+        {JwksStrategy, [domain: domain]}
+      end)
 
     # See https://hexdocs.pm/elixir/Supervisor.html
     # for other strategies and supported options

lib/cloudflare_access_ex/config.ex

@@ -0,0 +1,70 @@
+defmodule CloudflareAccessEx.Config do
+  @moduledoc """
+  Utility functions for processing the configuration of the library.
+  """
+
+  @spec get_issuer(String.t()) :: String.t()
+  @doc """
+  Get the issuer URL for a domain. By default, just the domain name is provided, but it
+  is also possible to provide a full URL. This function will ensure that the issuer URL
+  is a full URL.
+  """
+  def get_issuer(domain) do
+    if String.match?(domain, ~r/^https?\:\/\//) do
+      domain
+    else
+      "https://#{domain}"
+    end
+  end
+
+  @spec resolve_domain(atom() | String.t()) :: String.t()
+  @doc """
+  Given a domain atom or string, return the domain string.
+
+  If the domain is an atom, it will be looked up in the application config.
+  """
+  def resolve_domain(domain) when is_atom(domain) do
+    resolved_domain =
+      Application.get_env(:cloudflare_access_ex, domain, [])
+      |> Keyword.get(:domain) ||
+        throw(
+          "Attempting to get domain name for :cloudflare_access_ex, #{inspect(domain)} but no :domain key found in config"
+        )
+
+    if is_binary(resolved_domain) do
+      resolved_domain
+    else
+      throw(
+        "Domain configuration #{inspect(domain)} refers to #{inspect(resolved_domain)} which is not a string"
+      )
+    end
+  end
+
+  def resolve_domain(domain) when is_binary(domain),
+    do: domain
+
+  def resolve_domain(domain),
+    do: throw("Invalid domain name: #{inspect(domain)}")
+
+  @spec get_domain_strings :: list(String.t())
+  @doc """
+  Return all domain names in all keys under :cloudflare_access_ex.
+  """
+  def get_domain_strings() do
+    Application.get_all_env(:cloudflare_access_ex)
+    |> get_domain_strings()
+  end
+
+  defp get_domain_strings(config) do
+    config
+    |> Enum.map(fn
+      {_, configs} when is_list(configs) ->
+        Keyword.get(configs, :domain)
+
+      _ ->
+        nil
+    end)
+    |> Enum.filter(&is_binary/1)
+    |> Enum.uniq()
+  end
+end