GranularPermissions 1.0.3

GranularPermissions

The world's most over-engineered permissions system.

Features

• Generic nodes (not tied to a resource)
• Resource-bound nodes, evaluated with respect to a particular resource marked IPermissionManaged
• Simple chains allow/deny grants with respect to an identifier (e.g. user ID)
  • Evaluated one after each other in order of provided Index to come up with a final pass/fail answer
• Default disallow policy if no matching grants
• Complex resource-bound grants using a DSL which is compiled into AST transformation at startup and then evaluated at runtime
• AspNetMvc (Core) extensions for registering services, logging permissions for debugging etc

Terminology

• Node: A permission entry. Something that can be done that needs its access controlled.
  • These have a key which by convention is represented as EntityName.[SubGroup].Action.
• Grants: Allow/deny rules that cover a single permission node. Can be typed as Generic or ResourceBound.
• ResourceBound grant: Evaluation of the grant must be performed in the context pf a resource.
  • For example, Product.Edit probably requires the product in question to be considered when checking to see if the user should have the permission or not.
• Generic grant: Does not require a resource when evaluating. E.g. Product.Create.
• Chain: grants are organised into chains and have identifiers within a chain. When nodes are checked, all grants that match the identifier in the specified chain are considered.
  • Example chains: Groups or Users
  • Example identifiers: Group ID or User ID
• Condition: An additional requirement on top of a ResourceBound grant. Written in a DSL for this permissions system.

DSL examples

new Cat
{
    Breed = CatBreed.Bengal,
    Age = 10,
    Name = "Felix"
}

You could write some conditions for a resource bound grant on node Cat.Adopt:

resource.Name == "Felix" || resource.Age < 10

resource.Age != 5

Supported operators: <=, >=, <, >, &&, ||, ., ==, !=, !, ~= (regex)

Usage

From an ASP.NET MVC Core project, in ConfigureServices in Startup.cs:

services.AddScoped<IPermissionGrantProvider, SomePermissionGrantProvider>();
services.AddGranularPermissions(typeof(Permissions));

SomePermissionGrantProvider must implement IPermissionGrantProvider. Its role is to return all grants (which implement IPermissionGrantSerialized) persisted in the system. You may wish to retrieve them from a database, for instance.

The Permissions class must define all permission nodes you wish to exist in your project:

public static class Permissions
{
    public static class Product
    {
        public static readonly ResourceNode<ProductModel> View =
            new ResourceNode<ProductModel>("Product.View", "View an individual product");
        
        public static readonly GenericNode Create =
            new GenericNode("Product.Create", "Create a product");
        
        public static readonly ResourceNode<ProductModel> Buy =
            new ResourceNode<ProductModel>("Product.Purchase", "Purchase an individual product");
    }
    
    public static class Cat
    {
        public static readonly ResourceNode<ProductModel> Pet =
            new ResourceNode<ProductModel>("Cat.Pet", "Pet the cat without being bitten/scratched");
        
        public static readonly GenericNode Adopt =
            new GenericNode("Cat.Adopt", "Be adopted by a cat");
    }
}

To check a permission within a specified chain, call GetResultUsingChain on the IPermissionsService instance which will return a PermissionResult (Unset, Allow or Deny).

It is possible to reload the grants at runtime by calling ReplaceAllGrants with a new IEnumerable<IPermissionGrantSerialized>.

Example use-case

A web application has two groups which have different levels of access. Group 1 is for "Everyone" and includes a basic level of permission grants. Group 2, "Administrators" includes a higher level of access for a subset of application users who are in this group.

Within GranularPermissions, you'd have:

• One chain, "Groups"
• A set of IPermissionGrantSerialized for the "Groups" chain with Identifier=1. These will apply to all users in the Everyone group.
• A set of IPermissionGrantSerialized for the "Groups" chain with Identifier=2. These will apply to all users in the Administrators group.
• Some IPermissionGrantProvider which returns the aforementioned IPermissionGrantSerialized instances from DB

A simple permissions checker would call GetResultUsingChain("Groups", Permissions.Node.ToCheck, groupId) for each of the user's groups and then aggregate the results to come up with a final allowed/denied result. For example, the administrators group may be considered a higher priority than the everyone group.

For resource bound nodes, it's simply a case of passing an additional argument GetResultUsingChain("Groups", Permissions.Node.ToCheckWithResource, groupId, resourceToCheckAgainst).

TODO

• Add ability to register DSL functions/identifiers