Configuring Permission Rules ============================ .. contents:: Table of contents :backlinks: none :depth: 3 :local: Introduction ------------ Access control rules in Hasura are defined at a role, table and action (*insert, update, select, delete*) level granularity: .. thumbnail:: ../../../../img/graphql/manual/auth/permission-rule-granularity.png :alt: Access control rules in Hasura Requests to Hasura should contain the reserved session variable ``X-Hasura-Role`` to indicate the requesting user's role, and the table and action information is inferred from the request itself. This information is used to determine the right permission rule to be applied (*if one has been defined*) to the incoming request. Hasura converts GraphQL queries (*or mutations/subscriptions*) into a single SQL query that is executed on the configured database instance. Hasura also includes constraints from permission rules in the SQL query itself. Permissions are essentially a combination of **boolean expressions** and **column selections** that impose constraints on the data being returned or modified. Let's take a look at the different configuration options available to define a permission rule. Permission rules are defined for each role, table, operation (*insert, select, update, delete*) by using the console or the :doc:`metadata APIs for permissions <../../api-reference/schema-metadata-api/permission>`. Operation permissions --------------------- **Select** permissions ^^^^^^^^^^^^^^^^^^^^^^ For ``select`` operations or for GraphQL queries, you can configure the following: * :ref:`row-level-permissions` * :ref:`col-level-permissions` * :ref:`aggr-query-permissions` * :ref:`limit-rows-permissions` **Insert** permissions ^^^^^^^^^^^^^^^^^^^^^^ For ``insert`` operations or for GraphQL mutations of the type *insert*, you can configure the following: * :ref:`row-level-permissions` * :ref:`col-level-permissions` * :ref:`col-presets-permissions` **Update** permissions ^^^^^^^^^^^^^^^^^^^^^^ For ``update`` operations or for GraphQL mutations of the type *update*, you can configure the following: * :ref:`row-level-permissions` * :ref:`col-level-permissions` * :ref:`col-presets-permissions` **Delete** permissions ^^^^^^^^^^^^^^^^^^^^^^ For ``delete`` operations or for GraphQL mutations of the type *delete*, you can configure the following: * :ref:`row-level-permissions` Permission categories --------------------- .. _row-level-permissions: Row-level permissions ^^^^^^^^^^^^^^^^^^^^^ Row-level premissions are **boolean expressions** that help you restrict access to rows depending on the operation being performed. E.g. in the case of ``select``, your boolean expression is run on every row to determine whether that row can be read. In the case of ``insert``, the boolean expression determines whether or not the mutation is allowed. Row-level permissions are defined using operators, static values, values in columns (*including those in related tables or nested objects*) and session variables. Using column operators to build rules ************************************* Type-based operators (*depending on the column type*) are available for constructing row-level permissions. You can use the same operators that you use to :doc:`filter query results <../../queries/query-filters>` along with a few others to define permission rules. See the :ref:`API reference ` for a list of all supported column operators. **For example**, the following two images illustrate the different operators available for ``integer`` and ``text`` types: .. thumbnail:: ../../../../img/graphql/manual/auth/operators-for-integer-types.png :width: 40% :alt: Column operators for integer types .. thumbnail:: ../../../../img/graphql/manual/auth/operators-for-text-types.png :width: 40% :alt: Column operators for text types Using boolean expressions ************************* The following is an example of a simple boolean expression to restrict access for ``select`` to rows where the value in the ``id`` column is greater than 10: .. thumbnail:: ../../../../img/graphql/manual/auth/simple-boolean-expression.png :alt: Using boolean expressions to build rules You can construct more complex boolean expressions using the ``_and``, ``_or`` and ``not`` operators: .. thumbnail:: ../../../../img/graphql/manual/auth/boolean-operators.png :alt: Using more complex boolean expressions to build rules **For example**, using the ``_and`` operator, you can construct a rule to restrict access for ``select`` to rows where the value in the ``id`` column is greater than 10 **and** the value in the ``name`` column starts with "a" or "A": .. thumbnail:: ../../../../img/graphql/manual/auth/composite-boolean-expression.png :alt: Example of a rule with the _and operator Using session variables *********************** Session variables that have been resolved from authentication tokens by either your authentication webhook or by Hasura using the JWT configuration are available for constructing row-level permissions. **For example**, to allow an ``author`` to access only their articles, you can use the ``X-Hasura-User-ID`` session variable to construct a rule to restrict access for ``select`` to rows in the ``articles`` table where the value in the ``id`` column is equal to the value in the session variable (*assuming this variable is being used to indicate the author's ID*): .. thumbnail:: ../../../../img/graphql/manual/auth/session-variables-in-permissions-simple-example.png :alt: Using session variables to build rules .. _relationships-in-permissions: Using relationships or nested objects ************************************* You can leverage :doc:`relationships <../../schema/relationships/index>` to define permission rules with fields from a nested object. **For example**, let's say you have an object relationship called ``agent`` from the ``authors`` table to another table called ``agent`` (*an author can have an agent*) and we want to allow users with the role ``agent`` to access the details of the authors who they manage in ``authors`` table. We can define the following permission rule that uses the aforementioned object relationship: .. thumbnail:: ../../../../img/graphql/manual/auth/nested-object-permission-simple-example.png :alt: Using a nested object to build rules This permission rule reads as "*if the author's agent's* ``id`` *is the same as the requesting user's* ``id`` *, allow access to the author's details*." .. admonition:: Array and object relationships work similarly - The above example would have worked even if the relationship were an array relationship. In our example, the corresponding rule for an array relationship would have read "*if any of this author's agents'* ``id`` *is the same as the requesting user's* ``id`` *, allow access to the author's details*". - You can also check out this more elaborate :ref:`example`. .. _unrelated-tables-in-permissions: Using unrelated tables / views ****************************** You can use the ``_exists`` operator to set a permission rule based on tables/views that are not related to our table. **For example**, say we want to allow a user to ``insert`` an ``article`` only if the value of the ``allow_article_create`` column in the ``users`` table is set to ``true``. Let's assume the user's id is passed in the ``X-Hasura-User-ID`` session variable. .. thumbnail:: ../../../../img/graphql/manual/auth/exists-permission-example.png :alt: Use an unrelated table to build rules This permission rule reads as "*if there exists a row in the table* ``users`` *whose* ``id`` *is the same as the requesting user's* ``id`` *and has the* ``allow_article_create`` *column set to true, allow access to insert articles*." .. _col-level-permissions: Column-level permissions ^^^^^^^^^^^^^^^^^^^^^^^^ Column-level permissions determine access to columns in the rows that are accessible based on row-level permissions. These permissions are simple selections: .. thumbnail:: ../../../../img/graphql/manual/auth/column-level-permissions.png :alt: Column level permissions In this example, the role ``author`` has only partial access to columns of the accessible rows for the ``select`` operation. .. _limit-rows-permissions: Row fetch limit ^^^^^^^^^^^^^^^ In the case of ``select`` operations, the number of rows to be returned in the response can be limited using this configuration: .. thumbnail:: ../../../../img/graphql/manual/auth/limit-rows-for-select.png :alt: Row fetch limit In the above example, this configuration restricts the number of accessible rows (*based on the rule*: ``{"id":{"_eq":"X-Hasura-User-Id"}}``) to 20. .. _aggr-query-permissions: Aggregation queries permissions ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ In the case of ``select`` operations, access to :doc:`aggregation queries <../../queries/aggregation-queries>` can be restricted for a given role using this configuration. .. thumbnail:: ../../../../img/graphql/manual/auth/aggregation-query-permissions.png :alt: Aggregation queries permissions In the above example, the role ``user`` is allowed to make aggregation queries. .. _col-presets-permissions: Column presets ^^^^^^^^^^^^^^ While this is strictly not a permission configuration, defining :doc:`role-based column presets <../../schema/default-values/column-presets>` on any column automatically removes access to it. This preset can be defined for ``insert`` and ``update`` operations. This configuration is also very useful to avoid sending sensitive user-information in the query and leverage session variables or static data instead.