Multi-tenant SaaS Applications with Keycloak's Group-Based Authorization

Question

Pulumi · Accepted Answer

Building a multi-tenant Software as a Service (SaaS) application involves setting up an authentication and authorization system that can handle different levels of access for different groups of users. Keycloak is an open-source Identity and Access Management solution that can help with this by providing group-based authorization.

Group-based authorization allows you to define access controls and permissions based on the groups a particular user belongs to. In a multi-tenant SaaS application, tenants could be considered as groups. Depending on which tenant (group) a user belongs to, they will have different access rights.

To manage group-based authorization in Keycloak using Pulumi, you can utilize resources from the `pulumi_keycloak` module. You will need to create groups, assign users to those groups, and potentially define client roles and permissions associated with these groups.

Below is a Python program using Pulumi that sets up a basic structure for group-based authorization in a multi-tenant SaaS application:

```python
import pulumi
import pulumi_keycloak as keycloak

# Assume the Realm is already created and you have its ID.
realm_id = "my-realm"

# Define a new Group for a tenant.
tenant_group = keycloak.Group("tenant-a-group",
    realm_id=realm_id,
    name="Tenant A")

# Define a Keycloak Client, which represents your application interfacing with Keycloak for authentication and authorization.
client = keycloak.openid.Client("my-application-client",
    realm_id=realm_id,
    client_id="my-application",
    name="My Application",
    enabled=True,
    access_type="CONFIDENTIAL",
    standard_flow_enabled=True,
    implicit_flow_enabled=False,
    direct_access_grants_enabled=True)

# Assign a group policy to the client for group-specific access.
group_policy = keycloak.openid.ClientGroupPolicy("tenant-a-policy",
    realm_id=realm_id,
    resource_server_id=client.id,
    name="Tenant A Policy",
    groups=[{
        "id": tenant_group.id,
        "path": tenant_group.path.apply(lambda path: f"/{path}"),  # pulumi.Output transformation to get group path
        "extendChildren": False
    }],
    decision_strategy="UNANIMOUS")

# Assign a user to the Tenant A group.
user = keycloak.User("sample-user",
    realm_id=realm_id,
    username="user1")

user_group_membership = keycloak.UserGroups("user1-membership",
    realm_id=realm_id,
    user_id=user.id,
    group_ids=[tenant_group.id])

# Export Group and User IDs
pulumi.export("tenant_group_id", tenant_group.id)
pulumi.export("sample_user_id", user.id)
```
In this program:

1. We import the `pulumi` and `pulumi_keycloak` modules.
2. We define a group in Keycloak to represent a tenant in our application.
3. We create a Keycloak client that serves as the intermediary between your application and Keycloak's services.
4. We set up a group policy for the client to enforce permissions based on group membership. Here, we add the group we created for Tenant A.
5. We create a user and assign them to the Tenant A group to ensure that they are subject to the permissions defined by their group membership.
6. We export the IDs of the created group and user so they can be referenced outside the Pulumi program, if needed.

Remember that you need to have the Keycloak server and realm already set up before running this program, and provide the necessary realm ID.

This basic structure can be expanded with more refined permissions, multiple groups, and different policy configurations according to the needs of your SaaS application's authorization requirements. With group-based authorization, Keycloak will now handle user access based on the group assignments and policies you’ve defined, which is critical in a multi-tenant application environment.