aah Authorization

Since v0.7 Authorization, or access control, is the function of specifying access rights to resources. In other words, who has access to what.

Examples of authorization checks are:

• Is the user allowed to look at this webpage
• Edit this data
• View this button
• Or print to this printer?

Those are all decisions determining what a user has access to.

Table of Contents

• Permissions Defined
  • Levels of permission granularity
• Roles Defined
  • Implicit Roles
  • Explicit Roles
• Users Defined
• How to do Authorization check?
  • In Application
  • In View/Template file

Elements of Authorization

Authorization has three core elements that referenced quite a bit in aah- permissions, roles, and users.

Permissions Defined

Permissions are the most atomic level of a security policy and they are statements of functionality. Permissions represent what can be done in your application. A well formed permission describes a resource types and what actions are possible when you interact with those resources. Can you open a door? Can you read a file? Can you delete a customer record? Can you push a button?

Common actions for data-related resources are create, read, update, and delete, commonly referred to as CRUD.

It is important to understand that permissions do not have knowledge of who can perform the actions- they are just statements of what actions can be performed.

Levels of permission granularity

The permissions above all specify an actions (open, read, delete, etc) on a resource (door, file, customer record, etc). In aah, you can define a permission to any depth you like. Here are a few common permission levels in order of granularity.

• Resource Level - This is the broadest and easiest to build. A user can edit customer records or open doors. The resource is specified but not a specific instance of that resource.
• Instance Level - The permission specifies the instance of a resource. A user can edit the customer record for Apple or open the kitchen door.
• Attribute Level - The permission now specifies an attribute of an instance or resource. A user can edit the address on the Apple customer record.

Roles Defined

In the context of Authorization, Roles are effectively a collection of permissions used to simplify the management of permissions and users. So users can be assigned roles instead of being assigned permissions directly, which can get complicated with larger user bases and more complex applications. So, for example, a bank application might have an administrator role or a bank teller role.

There are two types of roles that you need to be aware of and aah supports both.

Implicit Roles

Most people view roles as what we define as an implicit role where your application implies a set of permissions because a user has a particular role as opposed to the role explicitly being assigned permissions or your application checking for those permissions. Role checks in code are generally a reflection of an implicit role. You can view patient data because you have the administrator role. You can create an account because you have the bank teller role. The fact that these names exist does not have a correlation to what the software can actually do. Most people use roles in this manner. It is easiest but it can create a lot of maintenance and management problems for all the but the simplest application.

Explicit Roles

An explicit role has permissions explicitly assigned to it and therefore is an explicit collection of permissions. Permission checks in code are a reflection of an explicit role. You can view patient data because because you have the view patient data permission as part of your administrator role. You can create an account because you have the create account permission as part of your bank teller role. You can perform these actions, not because of some implicit role name based on a string but because the corresponding permission was explicitly assigned to your role.

The big benefits of explicit roles are easier manageability and lower maintenance of your application. If you ever need to add, remove, or change a role, you can do so without touching your source code.

Users Defined

A user is the who of an application. In aah, though; the concept of a user is really the Subject instance. aah use word Subject instead of user because user usually implies a human being and in aah a Subject can be anything interacting with your application– whether it be a human or a service.

Users are allowed to perform certain actions in your application through their association with roles or direct permissions. So you are able to open a customer record because you’ve been assigned the open customer record permission, either through a role you’ve been assigned or through a direct permission assignment.

For more information on Users, aka Subjects, please check out the Understanding Subject in aah documentation.

How to do Authorization check?

In Application

aah supports Authorization check by Configuration and Go code.

Via Configuration

Since v0.11.0 Define roles and permissions per route in routes.conf; aah does the Authorization check automatically using provided configuration for the Route. On failure, it calls Error Handling flow.

# Authorization (access rights/privileges)
authorization {
  # Satisfy value is used to evaluate the result of `roles` and `permissions` attribute.
  #
  # Possible values are
  #   - `either` => either roles or permissions should satisfy for Subject
  #   - `both`   => both roles and permissions should satisfy for Subject
  #
  # Default value is `either`.
  satisfy = "either"

  # Roles (Optional config)
  # Result of role function is evaluated as AND.
  #
  # Supported functions are `hasrole`, `hasanyrole`, `hasallroles`.
  # Roles are comma(,) separated values.
  roles = [
    "hasrole(manager)",
    "hasanyrole(role1, role2, role3)"
  ]

  # Permissions (Optional config)
  # Doc: https://docs.aahframework.org/security-permissions.html
  #
  # Result of permission function is evaluated as AND.
  #
  # Supported functions are `ispermitted`, `ispermittedall`.
  # Permissions are pipe(|) separated values.
  permissions = [
    "ispermitted(newsletter:read,write)",
    "ispermittedall(newsletter:read,write | newsletter:12345)"
  ]
}

Via Go code

The user can check the roles and permissions programmatically on Go code with structures like if and else blocks.

Firstly, get access to the current Subject/User. Then, call appropriate authorization methods with Subject instance.

subject := ctx.Subject()

Authorization Methods

For Example-

// Checks if Subject has role `administrator`.
if ctx.Subject().HasRole("administrator") {
  // allow access
} else {
  // don't allow access
}

// Checks if Subject has permission to read and edit newsletter.
if ctx.Subject().IsPermitted("newsletter:read,write") {
  // allow access
} else {
  // don't allow access
}

In View/Template file

aah provides templates/view functions to perform authorization in a flexible way on view files.

• hasrole
• hasanyrole
• hasallroles
• ispermitted
• ispermittedall

For Example:

Checks if Subject has permission to manage users. If true, then shows the link.

<html>
<body>
  {{ if ispermitted . "users:manage" }}
    <a href="/manage-users.html">Manage Users</a>
  {{ end }}
</body>
</html>

Attribution

This documentation includes content from Shiro security library.