AIP-56 Extensible user management

Status

Motivation

Today, the user management is part of core Airflow. Users, roles and permissions are stored in the Airflow metastore and managed through Flask-AppBuilder (FAB). Any additional feature in the user management part of Airflow means modifying core Airflow and more importantly, verifying it fits everyone needs from individuals to teams within enterprises.

For context, this had been brought up in a discussion regarding multi tenancy. It had been suggested that, instead of adding new features in the user management part of Airflow (such as having tenants), to extract this part of core Airflow and move it to a new component in Airflow: the auth manager. The target is, like executors, to have a generic interface defining the common API/functions of all auth managers which they need to implement. This way, Airflow would offer a pluggable/extensible way to define and use the auth manager that suits user needs. As opposed to the generic interface, the different auth manager implementations are not part of core Airflow and reside, depending on the service used underneath, in their respective provider (e.g AWS, Google) if it exists or in a new provider if it does not.

Proposal

The proposal is to extract the whole user management part of Airflow outside of core Airflow and introduce the auth manager. The goal of the auth manager is to manage all features and resources related to users, roles and permissions. This way users could simply chose between a very minimalist/simple auth manager and a more advanced one with notion of groups/tenants. Everything under the FAB security manager as it exists today is extracted out from core Airflow and handled by the auth manager.

The auth manager interface (or base auth manager) is an interface each auth manager needs to inherit from. This interface defines the common API of a auth manager and is the only integration point with core Airflow. In other words, any action related to user management is done through classes inheriting from this interface.
Since it is impossible to forecast what feature/view each auth manager is going to offer, the “Security” tab in the nav bar will be configured by each auth manager.
Auth managers are “pluggable”, meaning you can swap them based on your installation needs. Airflow can only have one auth manager configured at a time; this is set by the auth_manager option in the [core] section of the configuration file.

Implementations

In order to explain more into details how auth managers work, I decided to take two different implementations of auth manager:

• FAB auth manager. This auth manager offers the exact same features and experience as the current user management in Airflow. The implementation of this auth manager is part of this AIP.
• KeyCloak auth manager. This auth managers leverages KeyCloak to manager users and roles. The implementation of this auth manager is not part of this AIP. I still decided to include diagrams and explanations about this auth manager in this AIP to increase clarity and understanding about the potential different implementations of auth manager.

Minimalist FAB auth manager (backward compatible)

The target of the FAB auth manager is to offer a backward compatible experience to the users. To put it simple, it moves the FAB security manager out of core Airflow to a new provider: the FAB provider. All the different pages are still served through the web server. The “Security” tab is configured to be as it is today. End users should see no difference between before auth managers and after.

KeyCloak auth manager

The target of the KeyCloak auth manager is to delegate the user management to KeyCloak. The whole user management part is delegated to KeyCloak and admins have to configure roles and permissions in KeyCloak directly. A new provider KeyCloak needs to be created and contain only the KeyCloak auth manager. This auth manager will not be part of this AIP.

Authentication flow

The authentication flow allows a user to log in Airflow. The flow follows the oauth 2.0 protocol.

When the authentication succeeds, a Flask session is created as it is today. This Flask session stores the user information about the user that is connected. Depending on the auth manager the kind of information stored can vary but, as an example, if the auth manager service used follows OpenID Connect (OIDC), the OIDC access token will be stored in the Flask session so it can be used anytime throughout the user session.

To simplify the example diagrams below, we consider the user is not logged in and the authentication on the backend side succeed.

FAB auth manager

FAB auth manager is different from the other auth managers. Instead of delegating the login experience to an external service, it includes and defines the login page within the manager. The page is still served through the web server. The goal is to have the login page as it is today.

KeyCloak auth manager

Authorization flow

The is_authorized API is the API each auth manager needs to implement to check whether the current user has permissions to make a specific action. This API provides as well some context about the action being made and the resource being accessed so that the auth manager can make some authorization decisions based on multiple parameters. This context needs to be extensible so that it is easy to add new information to it. You can find the schema of this context below. It is represented as JSON for readability purposes but since is_authorized is a classic Python class method, they will be regular Python parameters.

{
	"action": "POST|GET|PUT|DELETE",
	"resource-type": "<resource-type>",
	"resource-details": {
		"id": "<resource-id>",
		"tags": [<resource-tag-1>, <resource-tag-2>],
        <other-resource-specific-information>,
	},
}

• action. Create (POST), Read (GET), Update (PUT) or Delete (DELETE) operation. 
• resource-type. The type of resource being accessed. The different values of this parameter are the list of resources already defined in Airflow today (you can see this list in Security → Resources in Airflow UI).
• resource-details (optional). This is an optional extensible object to provide more metadata about the resource being accessed
  • id (optional). The resource ID. If resource is "DAG", then this parameter relates to the DAG ID, if resource is "Variable", it relates to the Variable ID, etc...
  • tags (optional). List of tags associated to the resource. Only available for resources you can tag, e.g. DAGs.
  • This object is extensible, as such, other parameters can be added to this object to provide more information about the resource. e.g. "dag-folder", if resource is "DAG", specifies the DAG folder where the DAG is defined.

Examples:

{
	"action": "POST",
	"resource-type": "Variable"
}

{
	"action": "GET",
	"resource-type": "Variable"
}

{
	"action": "GET",
	"resource-type": "Variable",
	"resource-details": {
		"id": "my-var-id",
	},
}

{
	"action": "DELETE",
	"resource-type": "DAG",
	"resource-details": {
		"id": "my-dag-id",
		"tags": ["example1", "example2"],
		"dag-folder": "/dags/marketing",
	},
}

In order to understand how this API is implemented in different auth managers, let’s take the use case of “User clicks on Variables in the Admin menu”.

FAB auth manager

The is_authorized API in the FAB auth manager checks if the current user has the specified permissions. The implementation is very close to check_authorization in the security manager.

KeyCloak auth manager

Airflow Rest API

As part of the Rest API, some resources are no longer managed by core Airflow but by auth managers: roles and users. Therefore, these APIs will be removed:

• User APIs
• Role APIs

However, some auth managers might need to define additional Rest API for their own needs. FAB auth manager is an example, in order to be backward compatible, the APIs listed above that are removed from core Airflow need to be redefined/moved from core Airflow to FAB auth manager. By default, no additional Rest API is defined in the base auth manager.

Airflow CLI

Among the sub-commands exposed by Airflow CLI, roles and users, similarly to the Rest API, need to be removed from core Airflow. Like the Rest API, some auth managers might need to define additional CLI commands (e.g. FAB auth manager).

UI

The different UI pages used to manage users and roles are no longer part of Core Airflow and moved to auth managers. Depending on the auth manager and its service/tool used underneath, two options are possibles:

• Use the UI provided by the service/tool directly to manage users and roles. This is the preferred option.
• Create UI pages in the auth manager to manage users and roles. This is the option chosen for the FAB auth manager.

Even though the preferred option is to delegate entirely the user management to auth managers, the second option is necessary to implement the FAB auth manager.

Auth manager API

All auth managers have a common API defined in the auth manager interface. You can find in the table below the common API needed from all auth managers. The different categories are just for documentation and grouping purposes but might not be reflected in the architecture/code.

Future work

Here are some examples of task that are not part of the AIP but can be done as follow-up once the AIP is completed.

• Create KeyCloak provider and KeyCloak auth manager within it
• Additional providers (e.g. AWS auth manager, Google auth manager)

Considerations

What problem does it solve?

Why is it needed?

Having a user management which fits everyone needs (from individuals to teams within enterprises) is impossible. Users need to have an extensible and pluggable way to use and define the user management they want.

Native user management support in cloud providers means that roles can be mapped directed to identity provider.  Currently, Airflow operators have to work around this and are unable to provide seamless RBAC in Airflow when running it on different cloud platforms.

Which users are affected by the change?

All users are impacted by the change. Though, by default Airflow would use the FAB auth manager that is backward compatible and users should not see any difference. Of course, if an admin decides to change the auth manager to use another one, then the whole user management experience of the environment would change.

What defines this AIP as "done"?

• The auth manager interface defined
• New provider FAB provider created
• FAB auth manager inhering from the auth manager interface defined. This FAB auth manager is part of the new provider: FAB provider. By default Airflow uses this auth manager