Unlocking Fine-Grained Authorization with Amazon Verified Permissions: An Underrated AWS Service

In today’s application landscape, a comprehensive authorization solution is crucial for maintaining security and compliance. Amazon Verified Permissions (AVP) is an (I feel) often-overlooked service that offers powerful, fine-grained authorization capabilities for custom applications. Let’s explore this AWS service and discover how it can enhance your application’s security posture.

As I have worked across different AWS implementations and application deployments, there is often a desire by developers to implement their own authorization services, write their own policy language, check permissions stored in various database technologies, and otherwise fragment the authorization process. AWS released Amazon Verified Permissions service a while ago, but I don't see it talked about very much, and for organizations which are heavily invested in AWS, I think it is a great drop in solution for permissions and authorization management.

What is Amazon Verified Permissions?

Amazon Verified Permissions is a fully managed, scalable authorization service designed for custom applications. It uses the Cedar policy language to define and enforce fine-grained permissions, allowing developers to externalize authorization logic and centralize policy management.

Key features of AVP include:

• Fine-grained authorization using roles and attributes
• Centralized policy management
• Integration with identity providers like Amazon Cognito
• Real-time authorization decisions
• Automated policy analysis for compliance and auditing

How Amazon Verified Permissions Works

AVP leverages the Cedar policy language, an open-source language designed for writing and evaluating authorization policies. Here’s a high-level overview of how it works:

1. Define your authorization model using Cedar policies
2. Store and manage these policies in AVP
3. When a user attempts an action, your application sends an authorization request to AVP
4. AVP evaluates the request against relevant policies and returns an ALLOW or DENY decision
5. Your application enforces the decision

Key Components of AVP

Policy Management and Validation

AVP provides tools for creating, storing, and managing Cedar policies. It also offers policy validation to ensure that your policies are correctly formatted and align with your defined schema.

Policy Querying and Auditing

The service includes features for analyzing and auditing policies, helping you identify potential security issues or overly privileged access.

Integrations and Extensibility

AVP can integrate with identity providers like Amazon Cognito and works alongside other AWS services to provide a comprehensive authorization solution.

Getting Started with AVP

Let’s walk through a basic example of using Amazon Verified Permissions with Python. First, you’ll need to set up your AWS credentials and install the boto3 library.

import boto3

# Create a Verified Permissions client
avp_client = boto3.client('verifiedpermissions')

# Define a simple policy
policy = {
    "Sid": "AllowViewDocument",
    "Effect": "Allow",
    "Principal": {"Identifier": "User::Alice"},
    "Action": "Document::View",
    "Resource": {"Identifier": "Document::ProjectReport"}
}

# Create a policy store
policy_store = avp_client.create_policy_store(
    name="MyAppPolicyStore"
)

# Create a policy in the policy store
created_policy = avp_client.create_policy(
    policyStoreId=policy_store['policyStoreId'],
    definition=policy
)

# Check authorization
auth_response = avp_client.is_authorized(
    policyStoreId=policy_store['policyStoreId'],
    principal={"EntityType": "User", "EntityId": "Alice"},
    action="Document::View",
    resource={"EntityType": "Document", "EntityId": "ProjectReport"}
)

print(f"Authorization decision: {auth_response['decision']}")

This example demonstrates creating a policy store, defining a simple policy, and checking authorization using AVP.

• The policy defined in the policy variable allows a User called Alice to perform the action Document::View only when the specific resource is a Document with an ID of ProjectReport.
• You can see in the is_authorized call, you pass in information about the principal, action, and resource, and then get an authorization decision.

Notice how similar this is to AWS' IAM policies! Within AVP, you can define many different policies, and then say you have an API, you can pass the information about the principal and what they are accessing from each API call into an is_authorized call to determine whether to allow the request to be returned as successful or not!

AVP vs. Traditional Authorization Methods

Compared to traditional in-app authorization, AVP offers several advantages:

1. Externalized authorization logic, simplifying application code
2. Fine-grained, context-aware access control
3. Centralized policy management
4. Real-time authorization decisions
5. Built-in policy analysis and auditing capabilities

Best Practices and Tips

When using Amazon Verified Permissions, consider the following best practices:

1. Design your authorization model carefully before implementation
2. Use policy templates to standardize and simplify policy creation
3. Regularly audit and analyze your policies
4. Leverage AVP’s integration capabilities with other AWS services
5. Use the test bench feature to validate policies before deployment

Performance Considerations

To optimize AVP usage:

1. Use bulk authorization when possible to reduce API calls
2. Implement response caching for frequently accessed resources
3. Design your policies to be as specific as possible to improve evaluation speed

Areas for Additional Consideration

As with any technology solution, there are always bound to be downsides and considerations to make.

1. Multi-cloud and hybrid-cloud limitations:
   • As a single identity provider, AVP has limitations in interoperability across the identity stack and in a multi-cloud world.
   • Additional solutions may be needed to integrate AVP with on-premises or multi-cloud environments
2. While Cedar is open-source completely, it is something released and maintained by AWS. So, if you are worried about that type of lock-in or dependency, it's important to consider this, as AVP is fully reliant on it. I think AWS has done a good job getting it out into the community, where you could decouple this from AVP if needed.

Conclusion

Amazon Verified Permissions is a powerful service that can enhance the security and manageability of your custom applications. By externalizing and centralizing authorization logic, AVP allows developers to focus on core application functionality while ensuring robust, fine-grained access control. As applications become more complex and security requirements become more stringent, services like AVP will have an increasingly crucial role in maintaining secure and compliant applications.