defmodule Ash.Policy.Authorizer do
defstruct [
:actor,
:resource,
:query,
:changeset,
:data,
:action,
:api,
:verbose?,
:scenarios,
:real_scenarios,
:check_scenarios,
policies: [],
facts: %{true => true, false => false},
data_facts: %{}
]
@type t :: %__MODULE__{}
alias Ash.Policy.{Checker, Policy}
@check_schema [
check: [
type: {:custom, __MODULE__, :validate_check, []},
required: true,
doc: """
A check is a tuple of `{module, keyword}`.
The module must implement the `Ash.Policy.Check` behaviour.
Generally, you won't be passing `{module, opts}`, but will use one
of the provided functions that return that, like `always()` or
`actor_attribute_matches_record(:foo, :bar)`. To make custom ones
define a module that implements the `Ash.Policy.Check` behaviour,
put a convenience function in that module that returns {module, opts}, and
import that into your resource.
```elixir
defmodule MyResource do
use Ash.Resource, authorizers: [Ash.Policy.Authorizer]
import MyCustomCheck
policies do
...
policy do
authorize_if my_custom_check(:foo)
end
end
end
```
"""
],
name: [
type: :string,
required: false,
doc: "A short name or description for the check, used when explaining authorization results"
]
]
@authorize_if %Ash.Dsl.Entity{
name: :authorize_if,
describe: "If the check is true, the request is authorized, otherwise run remaining checks.",
args: [:check],
schema: @check_schema,
examples: [
"authorize_if logged_in()",
"authorize_if actor_attribute_matches_record(:group, :group)"
],
target: Ash.Policy.Check,
transform: {Ash.Policy.Check, :transform, []},
auto_set_fields: [
type: :authorize_if
]
}
@forbid_if %Ash.Dsl.Entity{
name: :forbid_if,
describe: "If the check is true, the request is forbidden, otherwise run remaining checks.",
args: [:check],
schema: @check_schema,
target: Ash.Policy.Check,
transform: {Ash.Policy.Check, :transform, []},
examples: [
"forbid_if not_logged_in()",
"forbid_if actor_attribute_matches_record(:group, :blacklisted_groups)"
],
auto_set_fields: [
type: :forbid_if
]
}
@authorize_unless %Ash.Dsl.Entity{
name: :authorize_unless,
describe: "If the check is false, the request is authorized, otherwise run remaining checks.",
args: [:check],
schema: @check_schema,
target: Ash.Policy.Check,
transform: {Ash.Policy.Check, :transform, []},
examples: [
"authorize_unless not_logged_in()",
"authorize_unless actor_attribute_matches_record(:group, :blacklisted_groups)"
],
auto_set_fields: [
type: :authorize_unless
]
}
@forbid_unless %Ash.Dsl.Entity{
name: :forbid_unless,
describe: "If the check is true, the request is forbidden, otherwise run remaining checks.",
args: [:check],
schema: @check_schema,
target: Ash.Policy.Check,
transform: {Ash.Policy.Check, :transform, []},
examples: [
"forbid_unless logged_in()",
"forbid_unless actor_attribute_matches_record(:group, :group)"
],
auto_set_fields: [
type: :forbid_unless
]
}
@policy %Ash.Dsl.Entity{
name: :policy,
describe: """
A policy has a name, a condition, and a list of checks.
Checks apply logically in the order they are specified, from top to bottom.
If no check explicitly authorizes the request, then the request is forbidden.
This means that, if you want to "blacklist" instead of "whitelist", you likely
want to add an `authorize_if always()` at the bottom of your policy, like so:
```elixir
policy action_type(:read) do
forbid_if not_logged_in()
forbid_if user_is_denylisted()
forbid_if user_is_in_denylisted_group()
authorize_if always()
end
```
If the policy should always run, use the `always()` check, like so:
```elixir
policy always() do
...
end
```
""",
schema: [
description: [
type: :string,
doc: "A description for the policy, used when explaining authorization results"
],
access_type: [
type: {:one_of, [:strict, :filter, :runtime]},
doc: """
There are three choices for access_type:
* `:strict` - authentication uses *only* the request context, failing when unknown.
* `:filter` - this is probably what you want. Automatically removes unauthorized data by altering the request filter.
* `:runtime` - tries to add a filter before the query, but if it cannot, it fetches the records and checks authorization.
Be careful with runtime checks, as they can potentially cause a given scenario to fetch *all* records of a resource, because
it can't figure out a common filter between all of the possible scenarios. Use sparingly, if at all.
"""
],
condition: [
type: {:custom, __MODULE__, :validate_condition, []},
doc: """
A check or list of checks that must be true in order for this policy to apply.
If the policy does not apply, it is not run, and some other policy
will need to authorize the request. If no policies apply, the request
is forbidden. If multiple policies apply, they must each authorize the
request.
"""
]
],
args: [:condition],
target: Ash.Policy.Policy,
entities: [
policies: [
@authorize_if,
@forbid_if,
@authorize_unless,
@forbid_unless
]
]
}
@bypass %{
@policy
| name: :bypass,
auto_set_fields: [bypass?: true],
describe:
"A policy that, if passed, will skip all following policies. If failed, authorization moves on to the next policy"
}
@policies %Ash.Dsl.Section{
name: :policies,
describe: """
A section for declaring authorization policies.
Each policy that applies must pass independently in order for the
request to be authorized.
""",
examples: [
"""
policies do
# Anything you can use in a condition, you can use in a check, and vice-versa
# This policy applies if the actor is a super_user
# Addtionally, this policy is declared as a `bypass`. That means that this check is allowed to fail without
# failing the whole request, and that if this check *passes*, the entire request passes.
bypass actor_attribute_equals(:super_user, true) do
authorize_if always()
end
# This will likely be a common occurrence. Specifically, policies that apply to all read actions
policy action_type(:read) do
# unless the actor is an active user, forbid their request
forbid_unless actor_attribute_equals(:active, true)
# if the record is marked as public, authorize the request
authorize_if attribute(:public, true)
# if the actor is related to the data via that data's `owner` relationship, authorize the request
authorize_if relates_to_actor_via(:owner)
end
end
"""
],
entities: [
@policy,
@bypass
],
imports: [
Ash.Policy.Check.BuiltInChecks,
Ash.Filter.TemplateHelpers
],
schema: [
default_access_type: [
type: {:one_of, [:strict, :filter, :runtime]},
default: :filter,
doc: """
The default access type of policies for this resource.
See the access type on individual policies for more information.
"""
]
]
}
@sections [@policies]
@moduledoc """
An authorization extension for ash resources.
To add this extension to a resource, add it to the list of `authorizers` like so:
```elixir
use Ash.Resource,
...,
authorizers: [
Ash.Policy.Authorizer
]
```
# DSL Documenation
## Table of Contents
#{Ash.Dsl.Extension.doc_index(@sections)}
#{Ash.Dsl.Extension.doc(@sections)}
A resource can be given a set of policies, which are enforced on each call to a resource action.
For reads, policies can be configured to filter out data that the actor shouldn't see, as opposed to
resulting in a forbidden error.
See the [policy writing guide](policies.md) for practical examples.
Policies are solved/managed via a boolean satisfiability solver. To read more about boolean satisfiability,
see this page: https://en.wikipedia.org/wiki/Boolean_satisfiability_problem. At the end of
the day, however, it is not necessary to understand exactly how Ash takes your
authorization requirements and determines if a request is allowed. The
important thing to understand is that Ash may or may not run any/all of your
authorization rules as they may be deemed unnecessary. As such, authorization
checks should have no side effects. Ideally, the checks built-in to ash should
cover the bulk of your needs.
"""
require Logger
@behaviour Ash.Authorizer
use Ash.Dsl.Extension, sections: @sections
@impl true
def exception({:changeset_doesnt_match_filter, filter}, state) do
Ash.Error.Forbidden.Policy.exception(
scenarios: Map.get(state, :scenarios),
facts: Map.get(state, :facts),
policies: Map.get(state, :policies),
resource: Map.get(state, :resource),
action: Map.get(state, :action),
filter: filter
)
end
def exception(:must_pass_strict_check, state) do
Ash.Error.Forbidden.Policy.exception(
scenarios: Map.get(state, :scenarios),
facts: Map.get(state, :facts),
policies: Map.get(state, :policies),
resource: Map.get(state, :resource),
action: Map.get(state, :action),
must_pass_strict_check?: true
)
end
def exception(_, state) do
Ash.Error.Forbidden.Policy.exception(
scenarios: Map.get(state, :scenarios),
facts: Map.get(state, :facts),
policies: Map.get(state, :policies),
resource: Map.get(state, :resource),
action: Map.get(state, :action),
must_pass_strict_check?: true
)
end
@doc false
def validate_check({module, opts}) when is_atom(module) and is_list(opts) do
{:ok, {module, opts}}
end
def validate_check(module) when is_atom(module) do
validate_check({module, []})
end
def validate_check(other) do
{:ok, {Ash.Policy.Check.Expression, expr: other}}
end
def validate_condition(conditions) when is_list(conditions) do
Enum.reduce_while(conditions, {:ok, []}, fn condition, {:ok, conditions} ->
{:ok, {condition, opts}} = validate_check(condition)
if Ash.Helpers.implements_behaviour?(condition, Ash.Policy.Check) do
{:cont, {:ok, [{condition, opts} | conditions]}}
else
{:halt, {:error, "Expected all conditions to be valid checks"}}
end
end)
end
@doc false
def validate_condition(condition) do
validate_condition([condition])
end
@impl true
def initial_state(actor, resource, action, verbose?) do
%__MODULE__{
resource: resource,
actor: actor,
action: action,
verbose?: verbose?
}
end
@impl true
def strict_check_context(_authorizer) do
[:query, :changeset, :api, :resource]
end
@impl true
def check_context(_authorizer) do
[:query, :changeset, :data, :api, :resource]
end
@impl true
def check(authorizer, context) do
check_result(%{authorizer | data: context.data})
end
@impl true
def strict_check(authorizer, context) do
%{
authorizer
| query: context.query,
changeset: context.changeset,
api: context.api
}
|> get_policies()
|> do_strict_check_facts()
|> case do
{:ok, authorizer} ->
strict_check_result(authorizer)
{:error, error} ->
{:error, error}
end
end
defp strict_filter(authorizer) do
{filterable, require_check} =
authorizer.scenarios
|> Enum.split_with(fn scenario ->
scenario
|> Enum.reject(fn {{check_module, opts}, _} ->
opts[:access_type] == :filter ||
match?(
{:ok, _},
Ash.Policy.Policy.fetch_fact(authorizer.facts, {check_module, opts})
) || check_module.type() == :filter
end)
|> Enum.empty?()
end)
filter = strict_filters(filterable, authorizer)
case {filter, require_check} do
{[], []} ->
:authorized
{_filters, []} ->
case filter do
[filter] ->
log(authorizer, "filtering with: #{inspect(filter)}, authorization complete")
{:filter, authorizer, filter}
filters ->
log(authorizer, "filtering with: #{inspect(or: filter)}, authorization complete")
{:filter, authorizer, [or: filters]}
end
{_filters, _require_check} ->
case global_filters(authorizer) do
nil ->
maybe_forbid_strict(authorizer)
{[single_filter], scenarios_without_global} ->
log(
authorizer,
"filtering with: #{inspect(single_filter)}, continuing authorization process"
)
{:filter_and_continue, single_filter,
%{authorizer | check_scenarios: scenarios_without_global}}
{filters, scenarios_without_global} ->
log(
authorizer,
"filtering with: #{inspect(and: filters)}, continuing authorization process"
)
{:filter_and_continue, [and: filters],
%{authorizer | check_scenarios: scenarios_without_global}}
end
end
end
defp strict_filters(filterable, authorizer) do
filterable
|> Enum.reduce([], fn scenario, or_filters ->
scenario
|> Enum.filter(fn {{check_module, check_opts}, _} ->
check_module.type() == :filter && check_opts[:access_type] in [:filter, :runtime]
end)
|> Enum.reject(fn {{check_module, check_opts}, result} ->
match?({:ok, ^result}, Policy.fetch_fact(authorizer.facts, {check_module, check_opts}))
end)
|> Enum.map(fn
{{check_module, check_opts}, true} ->
check_module.auto_filter(authorizer.actor, authorizer, check_opts)
{{check_module, check_opts}, false} ->
check_module.auto_filter_not(authorizer.actor, authorizer, check_opts)
end)
|> case do
[] ->
or_filters
[single] ->
[single | or_filters]
filters ->
[[and: filters] | or_filters]
end
end)
end
defp maybe_forbid_strict(authorizer) do
log(authorizer, "could not determine authorization filter, checking at runtime")
{:continue, %{authorizer | check_scenarios: authorizer.scenarios}}
end
defp global_filters(authorizer, scenarios \\ nil, filter \\ []) do
scenarios = scenarios || authorizer.scenarios
global_check_value =
Enum.find_value(scenarios, fn scenario ->
Enum.find(scenario, fn {{check_module, _opts} = check, value} ->
check_module.type == :filter &&
Enum.all?(scenarios, &(Map.fetch(&1, check) == {:ok, value}))
end)
end)
case global_check_value do
nil ->
case filter do
[] ->
nil
filter ->
{filter, scenarios}
end
{{check_module, check_opts}, required_status} ->
additional_filter =
if required_status do
check_module.auto_filter(authorizer.actor, authorizer, check_opts)
else
check_module.auto_filter_not(authorizer.actor, authorizer, check_opts)
end
scenarios = remove_clause(authorizer.scenarios, {check_module, check_opts})
new_facts = Map.put(authorizer.facts, {check_module, check_opts}, required_status)
global_filters(%{authorizer | facts: new_facts}, scenarios, [additional_filter | filter])
end
end
defp remove_clause(scenarios, clause) do
Enum.map(scenarios, &Map.delete(&1, clause))
end
defp check_result(authorizer) do
Enum.reduce_while(authorizer.data, {:ok, authorizer}, fn record, {:ok, authorizer} ->
authorizer.scenarios
|> Enum.reject(&scenario_impossible?(&1, authorizer, record))
|> case do
[] ->
{:halt, {:error, :forbidden, authorizer}}
scenarios ->
scenarios
|> Ash.Policy.SatSolver.remove_irrelevant_clauses()
|> do_check_result(authorizer, record)
end
end)
end
defp do_check_result(cleaned_scenarios, authorizer, record) do
if Enum.any?(cleaned_scenarios, &scenario_applies?(&1, authorizer, record)) do
{:cont, {:ok, authorizer}}
else
check_facts_until_known(cleaned_scenarios, authorizer, record)
end
end
defp scenario_applies?(scenario, authorizer, record) do
Enum.all?(scenario, fn {clause, requirement} ->
case Map.fetch(authorizer.facts, clause) do
{:ok, ^requirement} ->
true
_ ->
scenario_applies_to_record?(authorizer, clause, record)
end
end)
end
defp scenario_applies_to_record?(authorizer, clause, record) do
case Map.fetch(authorizer.data_facts, clause) do
{:ok, ids_that_match} ->
pkey = Map.take(record, Ash.Resource.Info.primary_key(authorizer.resource))
MapSet.member?(ids_that_match, pkey)
_ ->
false
end
end
defp scenario_impossible?(scenario, authorizer, record) do
Enum.any?(scenario, fn {clause, requirement} ->
case Map.fetch(authorizer.facts, clause) do
{:ok, value} when value != requirement ->
true
_ ->
scenario_impossible_by_data?(authorizer, clause, record)
end
end)
end
defp scenario_impossible_by_data?(authorizer, clause, record) do
case Map.fetch(authorizer.data_facts, clause) do
{:ok, ids_that_match} ->
pkey = Map.take(record, Ash.Resource.Info.primary_key(authorizer.resource))
not MapSet.member?(ids_that_match, pkey)
_ ->
false
end
end
defp check_facts_until_known(scenarios, authorizer, record) do
new_authorizer =
scenarios
|> find_fact_to_check(authorizer)
|> check_fact(authorizer)
scenarios
|> Enum.reject(&scenario_impossible?(&1, new_authorizer, record))
|> case do
[] ->
log(authorizer, "Checked all facts, no real scenarios")
{:halt, {:forbidden, authorizer}}
scenarios ->
cleaned_scenarios = Ash.Policy.SatSolver.remove_irrelevant_clauses(scenarios)
if Enum.any?(cleaned_scenarios, &scenario_applies?(&1, new_authorizer, record)) do
{:cont, {:ok, new_authorizer}}
else
check_facts_until_known(scenarios, new_authorizer, record)
end
end
end
defp check_fact({check_module, check_opts}, authorizer) do
if check_module.type() == :simple do
raise "Assumption failed"
else
authorized_records =
check_module.check(authorizer.actor, authorizer.data, authorizer, check_opts)
pkey = Ash.Resource.Info.primary_key(authorizer.resource)
pkeys = MapSet.new(authorized_records, &Map.take(&1, pkey))
%{
authorizer
| data_facts: Map.put(authorizer.data_facts, {check_module, check_opts}, pkeys)
}
end
end
defp find_fact_to_check(scenarios, authorizer) do
scenarios
|> Enum.concat()
|> Enum.find(fn {key, _value} ->
not Map.has_key?(authorizer.facts, key) and not Map.has_key?(authorizer.data_facts, key)
end)
|> case do
nil -> raise "Assumption failed"
{key, _value} -> key
end
end
defp strict_check_result(authorizer) do
case Checker.strict_check_scenarios(authorizer) do
{:ok, scenarios} ->
report_scenarios(authorizer, scenarios, "Potential Scenarios")
case Checker.find_real_scenarios(scenarios, authorizer.facts) do
[] ->
maybe_strict_filter(authorizer, scenarios)
real_scenarios ->
report_scenarios(authorizer, real_scenarios, "Real Scenarios")
:authorized
end
{:error, :unsatisfiable} ->
{:error,
Ash.Error.Forbidden.Policy.exception(
facts: authorizer.facts,
policies: authorizer.policies,
resource: Map.get(authorizer, :resource),
action: Map.get(authorizer, :action),
scenarios: []
)}
end
end
defp maybe_strict_filter(authorizer, scenarios) do
log(authorizer, "No real scenarios, attempting to filter")
strict_filter(%{authorizer | scenarios: scenarios})
end
defp do_strict_check_facts(authorizer) do
case Checker.strict_check_facts(authorizer) do
{:ok, authorizer, new_facts} ->
{:ok, %{authorizer | facts: new_facts}}
{:error, error} ->
{:error, error}
end
end
defp get_policies(authorizer) do
%{
authorizer
| policies: Ash.Policy.Info.policies(authorizer.resource)
}
end
defp report_scenarios(%{verbose?: true}, scenarios, title) do
scenario_description =
scenarios
|> Enum.map(fn scenario ->
scenario
|> Enum.reject(fn {{module, _}, _} ->
module == Ash.Policy.Check.Static
end)
|> Enum.map(fn {{module, opts}, requirement} ->
[" ", module.describe(opts) <> " => #{requirement}"]
end)
|> Enum.intersperse("\n")
end)
|> Enum.intersperse("\n--\n")
Logger.info([title, "\n", scenario_description])
end
defp report_scenarios(_, _, _), do: :ok
defp log(%{verbose?: true}, message) do
Logger.info(message)
end
defp log(_, _), do: :ok
end
