Access control basics
=====================

.. contents:: Table of contents
  :backlinks: none
  :depth: 2
  :local:


Introduction
------------

To understand the basics of access control in Hasura, let's take a look at this analogy to a SQL query: 

.. thumbnail:: ../../../../img/graphql/manual/auth/permissions-rule-analogy.png
  :width: 70%

This query returns the right set of results by defining the requirements for columns and rows in a given
table. Hasura's rule-based access control works similary - you define the following permissions for a
combination of **role**, **table** and **action** (*insert, update, select and delete*):

**Row-level permissions**

Limit access to a subset of the rows in the table based on this permission. Row-level permissions are
essentially boolean expressions that, when evaluated against any row, determine access to it. These
permissions are constructed from the values in columns, :doc:`session variables <roles-variables>` and
static values to build this boolean expression.

**Column-level permissions**

For the rows that are accessible based on the above, limit access to a subset of the columns based on
this permission rule.

.. admonition:: More information

  For details on all the configuration options, see :doc:`permission-rules`.


Example
-------

Let's see access control in action using a simple example.

Create a table
^^^^^^^^^^^^^^

Head to your console and :ref:`create a table <create-tables>` called ``author`` with the following
schema:

.. code-block:: sql

  author (
    id INT PRIMARY KEY,
    name TEXT
  )

Now, insert some sample data into the table using the ``Insert Row`` tab of the ``author`` table.

Run a query **without** access control
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Head to the ``GraphiQL`` tab in your console and try out the below query:

.. code-block:: graphql

  query {
    author {
      id
      name
    }
  }

You'll see that this results in a response that contains all the authors because by default the GraphQL
query is accepted with **admin** permissions.

.. thumbnail:: ../../../../img/graphql/manual/auth/fetch-authors.png

Define access control rules
^^^^^^^^^^^^^^^^^^^^^^^^^^^

Now let's define an access control rule for the ``author`` table for a role ``users``. Head to the
**Permissions** section of the table (``Data`` --> <table> --> ``Permissions`` tab) and define permissions
as shown below:

.. thumbnail:: ../../../../img/graphql/manual/auth/permission-basics-simple-example.png


This permission rule reads as: "*For the role* ``user`` *, table* ``author`` *and operation* ``select``/``query``,
allow access to those rows where the value in the ``id`` *column is the same as the value in the*
``X-Hasura-User-ID`` *session variable*".

Run a query **with** access control
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Let's run the same query as above but now with the ``X-Hasura-Role`` and ``X-Hasura-User-ID`` session
variables also included to indicate role and user information. These session variables are passed in
the ``Request Headers`` section of ``GraphiQL`` as highlighted below:

.. thumbnail:: ../../../../img/graphql/manual/auth/permission-basics-query-with-access-control.png

As you can see, the results are now filtered based on the access control rule for the role ``user``
(*since that is the role indicated by the* ``X-Hasura-Role`` *session variable*) and the results are
restricted to only those rows where the value in the ``id`` column is equal to ``1`` (*as indicated by
the* ``X-Hasura-User-ID`` *session variable*).

As described in the :doc:`Introduction to Authentication and Authorization <index>` section of the docs,
your auth service is required to resolve authentication tokens into these session variables. See
:doc:`Reference - Session Variables<index>` for more details.

Next steps
----------

Read about roles and session variables at: :doc:`roles-variables`

See more detailed examples at: :doc:`Common access control examples<common-roles-auth-examples>`