How do I consume the REST API in .NET using a class library?

To consume a REST API in .NET using a class library, you can use the `HttpClient` class, which is part of the `System.Net.Http` namespace. Here are the steps to achieve this:

1. **Create a Class Library:**
   - Start by creating a new class library project in Visual Studio. This project will contain the code responsible for consuming the REST API.

2. **Install `System.Net.Http` NuGet Package:**
   - In your class library project, make sure to install the `System.Net.Http` NuGet package. This package provides the `HttpClient` class, which is essential for making HTTP requests.

3. **Write Code to Consume the REST API:**
   - Use the `HttpClient` class to make requests to the REST API. You can create methods in your class library that correspond to different API endpoints or operations.

   ```csharp
   using System;
   using System.Net.Http;
   using System.Threading.Tasks;

   public class ApiClient
   {
       private readonly HttpClient _httpClient;

       public ApiClient(string baseApiUrl)
       {
           _httpClient = new HttpClient
           {
               BaseAddress = new Uri(baseApiUrl)
           };
       }

       public async Task<string> GetResourceAsync(string endpoint)
       {
           HttpResponseMessage response = await _httpClient.GetAsync(endpoint);

           if (response.IsSuccessStatusCode)
           {
               return await response.Content.ReadAsStringAsync();
           }
           else
           {
               // Handle error, throw exception, or return null, based on your requirements.
               return null;
           }
       }
   }
   ```

   In the example above:
   - The `ApiClient` class is initialized with a base API URL.
   - The `GetResourceAsync` method sends a GET request to the specified endpoint and returns the response content as a string.

4. **Use the Class Library in Your Application:**
   - Reference the class library in your application project (e.g., a console application, web application, etc.).
   - Create an instance of the `ApiClient` class and use its methods to interact with the REST API.

   ```csharp
   class Program
   {
       static async Task Main(string[] args)
       {
           string baseApiUrl = "https://api.example.com";
           ApiClient apiClient = new ApiClient(baseApiUrl);

           string endpoint = "/resource";
           string result = await apiClient.GetResourceAsync(endpoint);

           Console.WriteLine(result);
       }
   }
   ```

   Replace the `baseApiUrl` and `endpoint` variables with your actual API base URL and endpoint.

Remember to handle exceptions, error cases, and implement additional methods as needed based on the specific requirements of your application and the REST API you are working with. Additionally, consider handling security aspects such as API authentication and authorization if required by the API.