User impersonation#

PrestoSQL has to be authenticated when accessing an external service through the connector. Typically it requires passing authentication credentials, which contain information on behalf of what user PrestoSQL connects. Such credentials are stored in connector properties file.

Any PrestoSQL user accesses the external service as the user configured in the connector properties. This approach has the following downsides:

  • No authorization policies, built-in into this external service, are able to recognize the actual PrestoSQL user. As a result any user, who authenticates to PrestoSQL and access the data with PrestoSQL, has the same permissions and is tracked as the same service user.

  • It is difficult to perform an audit of access of the external service, since every PrestoSQL user is seen as the same local user in the external service.

One way of solving this is to impersonate the PrestoSQL user as the local user in the external service. With this approach PrestoSQL authenticates in the external service using credentials stored in the connector properties file. Once it connects, it informs the external service that any further action in a given session should be performed on behalf of current PrestoSQL user. That way a PrestoSQL user alice becomes a local user alice in the external service. This requires the user that connects to the external service, which is configured in connector properties file, to be trusted in this system and to be allowed to impersonate other users.

When impersonating PrestoSQL users in the external service, PrestoSQL itself also requires authentication and proper access control configuration to ensure that users with valid credentials can be authenticated in the external service.

Note that the external service is required to support the impersonation mechanism, and actual details are different depending on the service.

The connectors that support user impersonation as the PrestoSQL user are shown in the Starburst connectors overview.

The Hive Connector also supports user impersonation when connecting to Hive Metastore or HDFS. However, the Hive connector doesn’t support PrestoSQL user to local user translation.

PrestoSQL user to local user translation#

The same actual user could be represented differently among services. For example, a PrestoSQL user alice_in_presto can be represented in the external service as alice_in_external_service. This requires a translation that details the mapping to use. You can specify the path to the translations file with auth-to-local.config-file in the connector properties file:

auth-to-local.config-file=etc/auth-to-local-rules.json

The config file is specified in JSON format, and contains the rules defining how PrestoSQL users are represented in the external service.

Refresh#

By default, when a change is made to the auth-to-local.config-file, PrestoSQL must be restarted to load the changes. There is an optional property to refresh the properties without requiring a PrestoSQL restart. The refresh period is specified in the connector properties file:

auth-to-local.refresh-period=10m

User translation rules#

These rules control the PrestoSQL user name translation to the external service local user name. The local user is calculated by the first matching rule read from top to bottom. If no rule matches, an error is raised. Each rule is composed of the following fields:

  • match (optional): determines if local user should be calculated from PrestoSQL user name (USER) or principal (PRINCIPAL). Defaults to USER.

  • pattern (required): regex to match against the value pointed with match.

  • substitution (optional): local user replacement for PrestoSQL user.

  • case (optional): determines if result local user should be lowercased (LOWER), upper cassed (UPPER) or case should remain (KEEP). Defaults to KEEP.

For example, if you want to impersonate PrestoSQL user alice to access the external system as user alice_in_the_external_system and bob as charlie, you can use the following rules:

{
  "rules": [
    {
      "match": "USER",
      "pattern": "alice",
      "substitution": "alice_in_the_external_system"
    },
    {
      "match": "USER",
      "pattern": "bob",
      "substitution": "charlie"
    }
  ]
}

If you want to impersonate PrestoSQL users with principals alice/hr@company.com and charlie/eng@company.com to access the external system as users HR_ALICE and ENG_CHARLIE accordingly, but PrestoSQL principals bob/marketing@company.com and danny/marketing@company.com to use marketing_acount, you can use the following rules:

{
  "rules": [
    {
      "match": "PRINCIPAL",
      "pattern": "[^/]+/marketing@company.com",
      "substitution": "marketing_acount"
    },
    {
      "match": "PRINCIPAL",
      "pattern": "([^/]+)/(.+)@company.com",
      "case": "UPPER",
      "substitution": "$2_1"
    }
  ]
}