Authorization Policy using Dependency Injection in asp.net core

Question

I want to create policy based authorisation for aspnet.core

I have lots of policies that I want to implement and I don't want to bloat the startup.cs file with policies.

public void ConfigureServices(IServiceCollection services)
{
    services.AddAuthorization(options =>
    {
        options
            .AddPolicy("Policy1", policyBuilder =>
            {
                policyBuilder
                    .RequireClaim("scope", "1")
                    .Build();
            }).AddPolicy("Policy2", policyBuilder =>
            {
                policyBuilder
                    .RequireClaim("scope", "2")
                    .Build();
            }).AddPolicy("Policy3", policyBuilder =>
            {
                policyBuilder
                    .RequireClaim("scope", "3")
                    .Build();
            }).AddPolicy("Policy4", policyBuilder =>
            {
                policyBuilder
                    .RequireClaim("scope", "4")
                    .Build();
                ;
            });
    });
}

I want to inject all the policies at startup.

Does anyone have any idea how to do this?

I thought about creating a factory that gets all the policies by reflection, but I really want to be able to inject classes into the policies.

e.g.

public interface IPolicy
{
    string Name { get; }
    AuthorizationPolicy AuthorizationPolicy { get; }
}

public class UserCreatePolicy : IPolicy
{
    public const string Name = "UserCreatePolicy";

    public UserCreatePolicy(IUserRoleService userRoleService)
    {
        _userRoleService = userRoleService;
    }

    public AuthorizationPolicy AuthorizationPolicy =>
        new AuthorizationPolicyBuilder()
            .RequireClaim("scope", _userRoleService.GetRole(1))
            .Build();
}

public class AuthorizationPolicyFactory
{
    public static void Create(AuthorizationOptions authorizationOptions)
    {
        typeof(IPolicy).Assembly
            .GetTypes()
            .Where(x => typeof(IPolicy).IsAssignableFrom(x) && !x.IsAbstract && !x.IsInterface)
            .ToList()
            .ForEach(type =>
            {
                if (Activator.CreateInstance(type) is IPolicy policy)
                {
                    authorizationOptions.AddPolicy(policy.Name, policy.AuthorizationPolicy);
                }
            });
    }
}

Ideally I don't want to have to use reflection and instead use Dependency injection.

NtFreX · Accepted Answer · 2017-10-03 09:22:31Z

You could use the IServiceProvider directly. Even if it is an anti pattern for such cases I see no way around.

public interface IPolicy
{
    string Name { get; }
    void ConfigurePolicy(AuthorizationPolicyBuilder builder);
}

public class UserCreatePolicy : IPolicy
{
    public string Name { get; } = "UserCreatePolicy";

    public UserCreatePolicy(IUserRoleService userRoleService)
    {
        _userRoleService = userRoleService;
    }

    public void ConfigurePolicy(AuthorizationPolicyBuilder builder)
    {
        builder
            .RequireClaim("scope", _userRoleService.GetRole(1))
            .Build();
    }
}

To configure this policies I've created an extension method.

public static class AuthorizationPolicyExtensions
{
    public static void ConfigureAuthorizationPolicies(this IServiceCollection serviceCollection, AuthorizationOptions authorizationOptions)
    {
        var policiesTypes = typeof(IPolicy).Assembly
            .GetTypes()
            .Where(x => typeof(IPolicy).IsAssignableFrom(x) && !x.IsAbstract && !x.IsInterface)
            .ToList();

        foreach (var type in policiesTypes)
        {
            serviceCollection.AddTransient(type);
        }

        var serviceProvider = serviceCollection.BuildServiceProvider();

        var policies = policiesTypes
            .Select(x => serviceProvider.GetService(x) as IPolicy)
            .Where(x => x != null);

        foreach (var policy in policies)
        {
            authorizationOptions.AddPolicy(policy.Name, policy.ConfigurePolicy);
        }
    }
}

It searches for IPolicy types and registers them in the inversion of control container. Then it will resolve those IPolicy's with the IServiceProvider and register them.

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