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Stream Policy Authorization

Tutorial: Setting up and using Stream Policy Authorization in KurrentDB

This step-by-step tutorial guides you through enabling and configuring Stream Policy Authorization in KurrentDB. This feature allows KurrentDB administrators to define stream access policies based on stream prefixes.

Prerequisites

Step 1: Verify license key

Ensure you have a valid license key to utilize Stream Policy Authorization. Without the license, this feature will not function.

Step 2 (optional): Confirm Stream Policy Authorization availability

By default, Stream Policy Authorization is bundled with KurrentDB 24.10 LTS. You can confirm its availability in the KurrentDB logs. Look for the following log message:

[INF] AuthorizationPolicyRegistryFactory Loaded Authorization Policy plugin: streampolicy

Refer to the log documentation for instructions on accessing KurrentDB logs.

Step 3: Enable Stream Policy Authorization

Note

When Stream Policy Authorization is enabled, KurrentDB will not enforce stream Access Control Lists (ACLs).*

To enable stream policies, append an event of type $authorization-policy-changed to the $authorization-policy-settings stream:

HTTP
POST https://localhost:2113/streams/$authorization-policy-settings
Authorization: Basic admin changeit
Content-Type: application/json
ES-EventId: 11887e82-9fb4-4112-b937-aea895b32a4a
ES-EventType: $authorization-policy-changed

{
    "streamAccessPolicyType": "streampolicy"
}

Step 4: Confirm Stream Policy Authorization activation

After enabling Stream Policy Authorization, you can confirm it is active by checking the log file. You should see the following log messages:

[22860,28,17:30:42.247,INF] StreamBasedAuthorizationPolicyRegistry New Authorization Policy Settings event received
[22860,28,17:30:42.249,INF] StreamBasedAuthorizationPolicyRegistry Starting factory streampolicy
...
[22860,28,17:30:42.264,INF] StreamBasedPolicySelector      Existing policy found in $policies stream (0)
[22860,28,17:30:42.269,INF] StreamBasedPolicySelector      Successfully applied policy
[22860,28,17:30:42.271,INF] StreamBasedPolicySelector      Subscribing to $policies at 0

If no valid license is detected, Stream Policy Authorization logs errors and defaults to the ACL policy settings. Refer to the Stream Policy Authorization documentation for a list of potential errors and their resolutions.

Step 5: Configure stream policies and rules

KurrentDB creates default stream policies by adding a default policy event in the $policies stream when the feature is enabled for the first time. The default policies specified in that event include:

  • Restricts system streams (i.e., streams that start with $) to the $admins group.
  • Grants users outside of the $ops group access to user streams (i.e., streams created by users of KurrentDB, excluding system streams) and their metadata.
  • Grants users outside of the $ops group read access to the default projection streams (i.e., streams that start with $ce,$et,$bc, $category, $streams) and their metadata.

You can create custom stream policies if you want to manage access more granularly. To do this, follow these steps:

  1. Identify users or user groups and their access permissions
    Start by determining the users and their roles within your system, along with the specific stream access permissions each role requires, such as read, write, or delete.

    For instance, you may identify the following users and their respective access permissions:

    UsersStreamsAccess permissions
    Users in the financeTeamStreams prefixed with finance-Read and metadata read permissions
    Users in the financeAdmin groupStreams prefixed with finance-Full permissions
    Users in the salesTeamStreams prefixed with sales-Read, write, and metadata read permissions
    Users in the salesAdmin groupStreams prefixed with sales-Full permissions
    Superuser ouroStreams prefixed with finance- or sales-Full permissions
    Other usersAny streamPermissions granted by the default stream policies

  2. Define custom policies in the $policies stream
    Policies control specific permissions, including read ($r), write ($w), delete ($d), metadata read ($mr), and metadata write ($mw).

    In this example, based on the users and permissions you identified in the previous step:

    • The custom policy financePolicy gives users in the financeTeam read and metadata read permissions, and superuser ouro and users in the financeAdmin group full permissions.
    • Similarly, the custom policy salesPolicy gives users in the salesTeam read, write, and metadata read permissions, and superuser ouro and users in the salesAdmin group full permissions.
     "streamPolicies": {  
   "financePolicy": {  
     "$r": ["ouro", "financeAdmin", "financeTeam"],  
     "$w": ["ouro", "financeAdmin"],  
     "$d": ["ouro", "financeAdmin"],  
     "$mr": ["ouro", "financeAdmin", "financeTeam"],  
     "$mw": ["ouro", "financeAdmin"] 
   },  
   "salesPolicy": {  
     "$r": ["ouro", "salesAdmin", "salesTeam"],  
     "$w": ["ouro", "salesAdmin", "salesTeam"],  
     "$d": ["ouro", "salesAdmin"],  
     "$mr": ["ouro", "salesAdmin", "salesTeam"],  
     "$mw": ["ouro", "salesAdmin"] 
   }  
  }

  3. Apply policies to stream prefixes You can apply custom or default policies to specific stream prefixes using streamRules. You can also apply the same policy to multiple streams by defining multiple stream rules.

    In this example, streams with the finance- and sales- prefixes use custom policies, while projection-related streams use the default projection policy.

    "streamRules": [  
  {  
    "startsWith": "finance-",  
    "policy": "financePolicy"  
  },
  {  
    "startsWith": "sales-",  
    "policy": "salesPolicy"  
  },
  {  
    "startsWith": "$et-",  
    "policy": "projectionsDefault"  
  },  
  {  
    "startsWith": "$ce-",  
    "policy": "projectionsDefault"  
  },  
  {    
    "startsWith": "$bc-",  
    "policy": "projectionsDefault"  
  },  
  {  
    "startsWith": "$category-",  
    "policy": "projectionsDefault"  
  },  
  {  
    "startsWith": "$streams",  
    "policy": "projectionsDefault"  
  }  
 ]

  4. Specify default stream rules
    You must still specify default stream rules when you update the $policies stream.

    "defaultStreamRules": {  
    "userStreams": "publicDefault", 
    "systemStreams": "adminsDefault"  
  }

    Combine the code from these three steps and follow the structure to configure a custom policy. The stream policies now include the custom policies you defined and, unless you want to remove or change them, the default policies created by the KurrentDB when Stream Policy Authorization is initially enabled.

    Click here to view the complete JSON code of the example above titled customPolicy.json.
    {
  "streamPolicies": {
    "financePolicy": {
      "$r": ["ouro", "financeAdmin", "financeTeam"],
      "$w": ["ouro", "financeAdmin"],
      "$d": ["ouro", "financeAdmin"],
      "$mr": ["ouro", "financeAdmin", "financeTeam"],
      "$mw": ["ouro", "financeAdmin"]
    },
    "salesPolicy": {
      "$r": ["ouro", "salesAdmin", "salesTeam"],
      "$w": ["ouro", "salesAdmin", "salesTeam"],
      "$d": ["ouro", "salesAdmin"],
      "$mr": ["ouro", "salesAdmin", "salesTeam"],
      "$mw": ["ouro", "salesAdmin"]
    },
    "publicDefault": {
      "$r": ["$all"],
      "$w": ["$all"],
      "$d": ["$all"],
      "$mr": ["$all"],
      "$mw": ["$all"]
    },
    "adminsDefault": {
      "$r": ["$admins"],
      "$w": ["$admins"],
      "$d": ["$admins"],
      "$mr": ["$admins"],
      "$mw": ["$admins"]
    },
    "projectionsDefault": {
      "$r": ["$all"],
      "$w": ["$admins"],
      "$d": ["$admins"],
      "$mr": ["$all"],
      "$mw": ["$admins"]
    }
  },
  "streamRules": [
    {
      "startsWith": "finance-",
      "policy": "financePolicy"
    },
    {
      "startsWith": "sales-",
      "policy": "salesPolicy"
    },
    {
      "startsWith": "$et-",
      "policy": "projectionsDefault"
    },
    {
      "startsWith": "$ce-",
      "policy": "projectionsDefault"
    },
    {
      "startsWith": "$bc-",
      "policy": "projectionsDefault"
    },
    {
      "startsWith": "$category-",
      "policy": "projectionsDefault"
    },
    {
      "startsWith": "$streams",
      "policy": "projectionsDefault"
    }
  ],
  "defaultStreamRules": {
    "userStreams": "publicDefault",
    "systemStreams": "adminsDefault"
  }
}

  5. Add custom policy to the $policies stream
    To add your custom policy configuration to the $policies stream, append an event of type $policy-updated to the $policies stream like below:

    HTTP
    POST https://localhost:2113/streams/$policies
Authorization: Basic admin changeit
Content-Type: application/json
ES-EventId: b04a64bf-4ac2-4f36-a856-6da9b63e64b7
ES-EventType: $policy-updated

 ./customPolicy.json

Step 6: Validate the policy configuration

After updating the $policies stream, ensure your policy update is applied correctly by checking the logs. You should see the following log message:

[INF] StreamBasedPolicySelector      New policy found in $policies stream (1)
[INF] StreamBasedPolicySelector      Successfully applied policy

If the policy is invalid, KurrentDB continues running with the previous valid policy, and an error is logged.

Step 7 (optional): Testing and monitoring policies

  1. Validate access controls
    Test the permissions by attempting access to streams under various prefixes as different users.

    For instance, given the code example in the tutorial, you should have the following test results:

    Test usersTest streamsAccess attemptsExpected result for each attempt
    user1 (a user in the financeTeam)finance-123Read or metadata readSuccess
    user1 (a user in the financeTeam)finance-123Write, delete, or metadata writeFailure
    user2 (a user in the financeAdmin group)finance-45Read, write, delete, metadata read, or metadata writeSuccess
    ourofinance-6Read, write, delete, metadata read, or metadata writeSuccess
    user4 (a user not in the financeTeam or the financeAdmin group)finance-7Read, write, delete, metadata read, or metadata writeFailure
    user3 (a user in the salesTeam)sales-456Read, write, or metadata readSuccess
    user3 (a user in the salesTeam)sales-456Delete or metadata writeFailure
    user2 (a user in the salesAdmin group)sales-78Read, write, delete, metadata read, or metadata writeSuccess
    ourosales-9Read, write, delete, metadata read, or metadata writeSuccess
    user5 (a user not in the salesTeam or the salesAdmin group)sales-10Read, write, delete, metadata read, or metadata writeFailure
    User6 (any user)account-123Read, write, delete, metadata read, or metadata writeSuccess

  2. Monitor logs for errors
    Errors in policy applications are logged. If any issues arise, KurrentDB maintains the last valid policy configuration. Adjust and repost policies as needed.

  3. Fallback policy
    If custom policies are invalid or the feature fails to load, KurrentDB restricts access to admins only, ensuring security. To resolve this, either update the $authorization-policy-settings stream with valid settings or revert to ACLs as outlined below.

Step 8 (optional): Disable Stream Policies Authorization (Reverting to ACLs)

If you want to disable the stream policies authorization and revert to ACLs, you can post an event to $authorization-policy-settings with streamAccessPolicyType set to acl:

HTTP
### Configure cluster to use acls
POST https://localhost:2113/streams/$authorization-policy-settings
Authorization: Basic admin changeit
Content-Type: application/json
ES-EventId: d07a6637-d9d0-43b7-8f48-6a9a8800af12
ES-EventType: $authorization-policy-changed

{
    "streamAccessPolicyType": "acl"
}

Summary

By following this tutorial, you should have successfully:

  • Enabled the Stream Policy Authorization feature.
  • Configured default and custom stream policies.
  • Applied stream access policies to specific stream prefixes.
  • Validated the stream policy configuration.

This setup ensures that your KurrentDB instance has tailored access control based on stream prefixes, making it easier to manage permissions and secure access to streams in your environment.

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