ABAC authorization - Amazon Identity and Access Management
Comparison of ABAC to the traditional RBAC model
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ABAC authorization

Attribute-based access control (ABAC) is an authorization strategy that defines permissions based on attributes. Amazon calls these attributes tags. You can attach tags to IAM resources, including IAM entities (IAM users or IAM roles) and to Amazon resources. You can create a single ABAC policy or small set of policies for your IAM principals. You can design ABAC policies can that allow operations when the principal's tag matches the resource tag. ABAC's attribute system that provides both high user context and granular access control. Because ABAC is attribute-based, it can perform dynamic authorization for data or applications that grants or revokes access in real time. ABAC is helpful in environments that are scaling and in situations where identity or resource policy management has become complex.

For example, you can create three IAM roles with the access-project tag key. Set the tag value of the first IAM role to Heart, the second to Star, and the third to Lightning. You can then use a single policy that allows access when the IAM role and the Amazon resource have the tag value access-project. For a detailed tutorial that demonstrates how to use ABAC in Amazon, see IAM tutorial: Define permissions to access Amazon resources based on tags. To learn about services that support ABAC, see Amazon services that work with IAM.

This diagram illustrates that the tags applied to a principal must match the tags applied to a resource for the user to be granted permissions to the resource. Tags be applied to user groups, resource groups, individual users and individual resources.

Comparison of ABAC to the traditional RBAC model

The traditional authorization model used in IAM is role-based access control (RBAC). RBAC defines permissions based on a person's job function, or role, which is distinct from an IAM role. IAM does include managed policies for job functions that align permissions to a job function in an RBAC model.

In IAM, you implement RBAC by creating different policies for different job functions. You then attach the policies to identities (IAM users, IAM groups, or IAM roles). As a best practice, you grant the minimum permissions necessary for the job function. This results in least privilege access. Each job function policy list the specific resources that identities assigned that policy can access. The disadvantage to using the traditional RBAC model is that when you or your users add new resources to your environment, you have to update the policies to allow access to those resources.

For example, assume that you have three projects, named Heart, Star, and Lightning, on which your employees work. You create an IAM role for each project. You then attach policies to each IAM role to define the resources that anyone allowed to assume the IAM role can access. If an employee changes jobs within your company, you assign them to a different IAM role. You can assign people or programs to more than one IAM role. However, the Star project might require additional resources, such as a new Amazon EC2 container. In that case, you have to update the policy attached to the Star IAM role to specify the new container resource. Otherwise, Star project members aren't allowed to access the new container.

This diagram illustrates that role-based access control requires that each identity be assigned a specific job-function based policy to access different resources.
ABAC provides the following advantages over the traditional RBAC model:

  • ABAC permissions scale with innovation. It's no longer necessary for an administrator to update existing policies to allow access to new resources. For example, assume that you designed your ABAC strategy with the access-project tag. A developer uses the IAM role with the access-project = Heart tag. When people on the Heart project need additional Amazon EC2 resources, the developer can create new Amazon EC2 instances with the access-project = Heart tag. Then anyone on the Heart project can start and stop those instances because their tag values match.

  • ABAC requires fewer policies. Because you don't have to create different policies for different job functions, you create fewer policies. Those policies are easier to manage.

  • Using ABAC, teams can dynamically respond to change and growth. Because permissions for new resources are automatically granted based on attributes you don't have to manually assign policies to identities. For example, if your company already supports the Heart and Star projects using ABAC, it's easy to add a new Lightning project. An IAM administrator creates a new IAM role with the access-project = Lightning tag. It's not necessary to change the policy to support a new project. Anyone that has permissions to assume the IAM role can create and view instances tagged with access-project = Lightning. Another scenario is when a team member moves from the Heart project to the Lightning project. To provide team member access to the Lightning project , the IAM administrator assigns them to a different IAM role. It's not necessary to change the permissions policies.

  • Granular permissions are possible using ABAC. When you create policies, it's a best practice to grant least privilege. Using traditional RBAC, you write a policy that allows access to specific resources. However, when you use ABAC, you can allow actions on all resources if the resource's tag matches the principal's tag.

  • Use employee attributes from your corporate directory with ABAC. You can configure your SAML or OIDC provider to pass session tags to IAM. When your employees federate into Amazon, IAM applies their attributes to their resulting principal. You can then use ABAC to allow or deny permissions based on those attributes.

For a detailed tutorial that demonstrates how to use ABAC in Amazon, see IAM tutorial: Define permissions to access Amazon resources based on tags.