A user can have many roles and each role can define different permissions on the same index. It is important to understand the behavior of document and field level security in this scenario.

Document level security takes into account each role held by the user and combines each document level security query for a given index with an "OR". This means that only one of the role queries must match for a document to be returned. For example, if a role grants access to an index without document level security and another grants access with document level security, document level security is not applied; the user with both roles has access to all of the documents in the index.

Field level security takes into account each role the user has and combines all of the fields listed into a single set for each index. For example, if a role grants access to an index without field level security and another grants access with field level security, field level security is not be applied for that index; the user with both roles has access to all of the fields in the index.

For example, let’s say role_a grants access to only the address field of the documents in index1; it doesn’t specify any document restrictions. Conversely, role_b limits access to a subset of the documents in index1; it doesn’t specify any field restrictions. If you assign a user both roles, role_a gives the user access to all documents and role_b gives the user access to all fields.

If you need to restrict access to both documents and fields, consider splitting documents by index instead.

When you create a role, you can specify a query that defines the document level security permissions. You can optionally use Mustache templates in the role query to insert the username of the current authenticated user into the role. Like other places in Elasticsearch that support templating or scripting, you can specify inline, stored, or file-based templates and define custom parameters. You access the details for the current authenticated user through the _user parameter.

For example, the following role query uses a template to insert the username of the current authenticated user:

POST /_security/role/example1
{
  "indices" : [
    {
      "names" : [ "my_index" ],
      "privileges" : [ "read" ],
      "query" : {
        "template" : {
          "source" : {
            "term" : { "acl.username" : "{{_user.username}}" }
          }
        }
      }
    }
  ]
}

You can access the following information through the _user variable:

You can also access custom user metadata. For example, if you maintain a group_id in your user metadata, you can apply document level security based on the group.id field in your documents:

POST /_security/role/example2
{
  "indices" : [
    {
      "names" : [ "my_index" ],
      "privileges" : [ "read" ],
      "query" : {
        "template" : {
          "source" : {
            "term" : { "group.id" : "{{_user.metadata.group_id}}" }
          }
        }
      }
    }
  ]
}

To guarantee that a user reads only their own documents, it makes sense to set up document level security. In this scenario, each document must have the username or role name associated with it, so that this information can be used by the role query for document level security. This is a situation where the Set Security User Processor ingest processor can help.

The set security user processor attaches user-related details (such as username, roles, email, full_name and metadata ) from the current authenticated user to the current document by pre-processing the ingest. When you index data with an ingest pipeline, user details are automatically attached to the document.

For more information see Ingest node and Set security user processor.