Added a new policy to require being an admin. Implemented ability to delete a user.

API/Controllers/AdminController.cs

@@ -26,10 +26,18 @@ namespace API.Controllers
         }
 
         [Authorize(Policy = "RequireAdminRole")]
-        [HttpDelete]
+        [HttpDelete("delete-user")]
         public async Task<ActionResult> DeleteUser(string username)
         {
-            return BadRequest("Not Implemented");
+            var user = await _userRepository.GetUserByUsernameAsync(username);
+            _userRepository.Delete(user);
+
+            if (await _userRepository.SaveAllAsync())
+            {
+                return Ok();
+            }
+            
+            return BadRequest("Could not delete the user.");
         }