feat: can implement faster hasPermission operations

Fixes #1

Author: pdevito3

README.md

@@ -343,7 +343,6 @@ For our [Database Store](#database-store) example above, we have the same 3 step
 **However it is implemented, the only thing that matters here is returning a list of strings as your final permissions.**
 
 ```c#
-
 public class DatabaseUserPolicyHandler : IUserPolicyHandler
 {
     private readonly RecipesDbContext _dbContext;
@@ -375,6 +374,46 @@ public class DatabaseUserPolicyHandler : IUserPolicyHandler
 }
 ```
 
+#### Enhancing Your `HasPermission` Checks
+
+The method `GetUserPermissions()` method requires all permissions for a user to be returned. When using a database, you might want to enhance the permformance of this call. You can do this by having your db use an `Exists` operation. To do this, you can implement the `HasPermission` method on your `UserPolicyHandler`. For example:
+
+```csharp
+
+public class DatabaseUserPolicyHandler : IUserPolicyHandler
+{
+    private readonly RecipesDbContext _dbContext;
+    private readonly IHttpContextAccessor _httpContextAccessor;
+
+    public UserPolicyHandler(RecipesDbContext dbContext, IHttpContextAccessor httpContextAccessor)
+    {
+        _dbContext = dbContext;
+        _httpContextAccessor = httpContextAccessor;
+    }
+    
+    public async Task<IEnumerable<string>> GetUserPermissions()
+    {
+        // ...
+    }
+  
+  	public async Task<bool> HasPermission(string permission)
+    {
+        var roles = await GetRoles();
+    
+        // super admins can do everything
+        if (roles.Contains(Role.SuperAdmin().Value))
+            return true;
+        
+        return await _dbContext.RolePermissions
+            .Where(rp => roles.Contains(rp.Role.Name))
+            .Select(rp => rp.Permission.Name)
+            .AnyAsync(x => x == permission);
+    }
+}
+```
+
+
+
 ### Registering HeimGuard
 
 Once you have your `IUserPolicyHandler` implementation set up, just go to your service builder and register HeimGuard like so:

src/HeimGuard/HeimGuardClient.cs

@@ -46,10 +46,7 @@ public HeimGuardClient(IUserPolicyHandler userPolicyHandler)
 
         /// <inheritdoc />
         public async Task<bool> HasPermissionAsync(string permission)
-        {
-            var policy = await _userPolicyHandler.GetUserPermissions();
-            return policy.Contains(permission);
-        }
+            => await _userPolicyHandler.HasPermission(permission);
 
         /// <inheritdoc />
         public async Task MustHavePermission<TException>(string permission) 

src/HeimGuard/IUserPolicyHandler.cs

@@ -1,6 +1,8 @@
 namespace HeimGuard
 {
     using System.Collections.Generic;
+    using System.Linq;
+    using System.Threading;
     using System.Threading.Tasks;
 
     /// <summary>
@@ -11,7 +13,13 @@ public interface IUserPolicyHandler
         /// <summary>
         /// Returns an IEnumerable of strings that represents a distinct list of a given user's permissions.
         /// </summary>
-        /// <returns><see cref="T:System.Threading.Tasks.Task" /> that represents the asynchronous operation, containing the list of peermissions for the current user..</returns>
+        /// <returns><see cref="T:System.Threading.Tasks.Task" /> that represents the asynchronous operation, containing the list of permissions for the current user.</returns>
         Task<IEnumerable<string>> GetUserPermissions();
+
+        /// <summary>
+        /// Returns a boolean value indicating whether the current user has the specified permission.
+        /// </summary>
+        /// <returns><see cref="T:System.Threading.Tasks.Task" /> that represents the asynchronous operation, containing a boolean indicating whether the current user has the specified permission.</returns>
+        async Task<bool> HasPermission(string permission) => (await GetUserPermissions()).Contains(permission);
     }
 }