Inherited Roles

Introduction

An inherited role is a way to create a new role which inherits permissions from two or more roles.

Once an inherited role is created, it can be treated as any other role i.e. it can be provided in the X-Hasura-Role session variable. An inherited role derives its roles from a role set.

Inherited roles are useful for when you need to define multiple permission rules which may use overlapping logic on schema objects and also for greater modularity in role management.

Supported from

Inherited roles are supported in all general availability (GA) versions of Hasura.

Creating inherited roles

Console

Inherited roles can be created in the Console by going to the Settings⚙️ tab and clicking on Inherited Roles.

Enter the new inherited role name and click "Create". Select the role set which will comprise it and click "Save Role" to save your new Inherited Role.

CLI

To add a new inherited role, edit the metadata -> inherited_roles.yaml file adding the inherited role definition like this:

- role_name: sample_inherited_role
  role_set:
    - user
    - editor

Apply the Metadata by running:

hasura metadata apply

API

You can add a inherited role using the add_inherited_role Metadata API:

POST /v1/metadata HTTP/1.1
Content-Type: application/json
X-Hasura-Role: admin

{
  "type": "add_inherited_role",
  "args": {
     "role_name":"sample_inherited_role",
     "role_set":[
        "user",
        "editor"
     ]
  }
}

Inherited roles cannot form cycles

For example:

Suppose there are two inherited roles: inherited_role1, inherited_role2 and two non-inherited roles: role1, role2 and:

• inherited_role1 inherits from role1 and inherited_role2

• inherited_role2 inherits from role2 and inherited_role1

The above configuration won't work because inherited_role1 and inherited_role2 form a cycle.

Overriding inherited roles

By default, inherited roles will inherit the permissions from its role set.

If you need to define a different permission than the inherited one for a particular entity and role pair, then it can be done by creating a separate specific permission. After creation, it will override the inherited permission, if any.

How the permissions of the inherited role are interpreted

1. Select permissions

A select permission is comprised of the following things:

1. Row selection filter
2. Columns accessible to the role
3. Limit
4. Allow aggregation
5. Scalar computed fields accessible to the role

Suppose there are two roles, role1 gives access to column C1 with row permission P1 and role2 gives access to columns C1 and C2 with row permission P2. Consider the following GraphQL query executed with an inherited role comprised of role1 and role2:

query {
  T {
    C1
    C2
  }
}

The above GraphQL query will be translated to the following SQL query.

select (case when (P1 or P2) then C1 else null end) as C1,
       (case when P2 then C2 else null end) as C2
from T
where (P1 or P2)

The other parameters of the select permission will be combined in the following manner:

1. Limit - Maximum of the limits will be the limit of the inherited role
2. Allow aggregations - If any of the role allows aggregation, then the inherited role will allow aggregation
3. Scalar computed fields - same as table column fields, as in the above example

Accessibility of a field for an inherited role

Accessibility of a field for an inherited role is defined as follows:

1. When all the roles give access to a column C, then C will always be accessible.
2. When not all, but some of the roles give access to the column C then the value of the column C will be outputted when the OR of P1,P2....P(n) is true and when it evaluates to false, the value of the column C will be null, where P is the row filter of the select permissions in which column C is given access to.
3. When none of the roles give access to column C, it won't be accessible to the inherited role.

Inherited select permissions Example 1

Let's take the example of an users table with the following columns:

1. id - Int - Primary key
2. name - Text
3. email - Text

There are two roles defined:

1. user - The user role will be able to access all columns of their row when the session variable X-Hasura-User-Id is equal to the id.
2. anonymous - The anonymous role will be able to access only the id and name columns of all the users.

Let's create a new inherited role called user_anonymous_inherited_role which inherits from the user and the anonymous roles.

1. Executing the query as user role

POST /v1/graphql HTTP/1.1
Content-Type: application/json
X-Hasura-Role: user
X-Hasura-User-Id: 1

GraphiQL

Query Variables

Request Headers

Documentation Explorer

⚲

No Schema Available

2. Executing the query as anonymous role

POST /v1/graphql HTTP/1.1
Content-Type: application/json
X-Hasura-Role: anonymous

GraphiQL

Query Variables

Request Headers

Documentation Explorer

⚲

No Schema Available

3. Executing the query as user_anonymous_inherited_role role

POST /v1/graphql HTTP/1.1
Content-Type: application/json
X-Hasura-Role: user_anonymous_inherited_role
X-Hasura-User-Id: 1

GraphiQL

Query Variables

Request Headers

Documentation Explorer

⚲

No Schema Available

In the response of the query being executed with the user_anonymous_inherited_role role, there are 3 rows returned and if we compare that to the queries executed as the user and anonymous roles, the results are unioned in the inherited role.

But some of the fields in some of the results have null values despite the value in the database not being null. This can only happen with inherited roles when a column doesn't have permission in the particular row. In the above example, we see that the email of "Bob" and "Sam" is null but is populated for "Alice" as the X-Hasura-User-Id session variable on the query is set to the corresponding id of that row.

The "Alice" row is executed as the user role and the other rows are executed as the anonymous role which is why the value is null.

Inherited select permissions Example 2

Suppose we have two tables, users and authors, and similarly two roles user and author are defined. The user role doesn't have permission to query the authors table and the author role doesn't have permission to query the users table. With only the user and the author role, we won't be able to construct a query which fetches data from both the tables. This can be solved by creating an inherited role out of user and author which can query both the tables in a single query.

POST /v1/graphql HTTP/1.1
Content-Type: application/json
X-Hasura-Role: user_authors_inherited_role
X-Hasura-User-Id: 1

GraphiQL

Query Variables

Request Headers

Documentation Explorer

⚲

No Schema Available

2. Mutation and Remote Schema permissions

A mutation (insert, update and delete) or Remote Schema permission is inherited in the following manner:

Suppose there's an inherited role R which inherits permissions from n roles in the set namely pr1, pr2, pr3 ...prn. The inherited permission for the role R on some entity can only be inherited when the permission on the entity is the same for all roles in the set.

For example, if two insert permissions are configured in the following way:

1. insert permission metadata of role pr1

   {
     "type": "pg_create_insert_permission",
     "args": {
       "table": "article",
       "source": "default",
       "role": "pr1",
       "permission": {
         "check": {
           "author_id": "X-HASURA-AUTHOR-ID"
         }
       }
     }
   }

2. insert permission metadata of the role pr2

   {
     "type": "pg_create_insert_permission",
     "args": {
       "table": "article",
       "source": "default",
       "role": "pr2",
       "permission": {
         "check": {
           "author_id": "X-HASURA-USER-ID"
         }
       }
     }
   }

The check constraint is different for each of the permissions and there's no way to resolve this conflict.

Whenever a conflict occurs while a role inherits from its role set, then the Metadata for that entity and role combination will be marked as inconsistent.

These can be seen by calling the get_inconsistent_metadata API. Following the above example, the role R which is trying to inherit permissions from the role pr1 and pr2 will be marked as inconsistent for the table permission of the table article.

This inconsistency is informational and can be ignored if the conflicting role entity pair is not going to be used. If this inconsistency needs to be resolved, then it can be done by adding a permission explicitly for the conflicting role entity pair.

3. Actions and Custom Functions permissions

Inheritance of permissions of Actions and custom functions work in the following way:

If any of the roles in the set have permission configured for a given Action or custom function, then the inherited role will also be able to access the given action or custom function.