How To Call Web API From An ASPX Page And Handle The Response

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When working with ASP.NET Web Forms applications, integrating with modern Web APIs is a common requirement. Whether you’re consuming internal APIs or third-party services, you may want to retrieve and display API data on an .aspx page. This article walks you through how to call Web API from an ASPX page and process the response using C#.

Project Scenario

You want to make an HTTP request (GET or POST) to an external or internal Web API from your ASPX code-behind (C#), read the response, and optionally deserialize the result (e.g., JSON).

Prerequisites

ASP.NET Web Forms application (.NET Framework)
A publicly accessible or internal RESTful API
Basic knowledge of HttpClient and JSON
Install-Package Newtonsoft.Json

Step-by-Step Implementation

Create a login page ASPX Page (Front-end UI)

<%@ Page Language="C#" Async="true" AutoEventWireup="true" CodeFile="Login.aspx.cs" Inherits="Login" %>

<!DOCTYPE html>
<html>
<head runat="server">
    <title>Login Page</title>
</head>
<body>
    <form id="form1" runat="server">
        <div>
            Username:
            <asp:TextBox ID="txtUsername" runat="server" />
            <br />
            Password:
            <asp:TextBox ID="txtPassword" runat="server" TextMode="Password" />
            <br />
            <asp:Button ID="btnLogin" runat="server" Text="Login" OnClick="btnLogin_Click" />
            <br />
            <asp:Label ID="lblResult" runat="server" ForeColor="Red" />
        </div>
    </form>
</body>
</html>

<%@ Page Language="C#" Async="true" AutoEventWireup="true" CodeFile="Login.aspx.cs" Inherits="Login" %>

<!DOCTYPE html>

<html>

<title>Login Page</title>

</head>

<body>

<div>

Username:

<asp:TextBox ID="txtUsername" runat="server" />

<br />

Password:

<asp:TextBox ID="txtPassword" runat="server" TextMode="Password" />

<br />

<asp:Button ID="btnLogin" runat="server" Text="Login" OnClick="btnLogin_Click" />

<br />

<asp:Label ID="lblResult" runat="server" ForeColor="Red" />

</div>

</form>

</body>

</html>

Code-Behind (Login.aspx.cs)

using System;
using System.Collections.Generic;
using System.Net.Http;
using System.Threading.Tasks;
using Newtonsoft.Json;
using System.Net.Http.Headers;

public partial class Login : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        // No async in Page_Load here, handled in button click
    }

    protected async void btnLogin_Click(object sender, EventArgs e)
    {
        string username = txtUsername.Text;
        string password = txtPassword.Text;

        string apiUrl = "https://yourdomain.com/api/v1/auth/login/"; // Replace with your actual API

        try
{
    using (HttpClientHandler handler = new HttpClientHandler())
    {
        handler.UseCookies = true;
        handler.CookieContainer = new System.Net.CookieContainer();

        using (HttpClient client = new HttpClient(handler))
        {
            // Set request header explicitly
            client.DefaultRequestHeaders.Accept.Clear();
            client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/x-www-form-urlencoded"));

            var formData = new FormUrlEncodedContent(new[]
            {
                new KeyValuePair<string, string>("username", username),
                new KeyValuePair<string, string>("password", password)
            });

            // Optional: Manually set the content type header on the content itself (though it's already handled)
            formData.Headers.ContentType = new MediaTypeHeaderValue("application/x-www-form-urlencoded");

            HttpResponseMessage response = await client.PostAsync(apiUrl, formData);

            if (response.IsSuccessStatusCode)
            {
                Uri uri = new Uri(apiUrl);
                var cookies = handler.CookieContainer.GetCookies(uri);
                foreach (System.Net.Cookie cookie in cookies)
                {
                    lblResult.Text += $"<br />Cookie: {cookie.Name} = {cookie.Value}";
                }
            }
            else
            {
                DisplayMessage("Login failed: " + response.StatusCode);
            }
        }
    }
}
catch (Exception ex)
{
    DisplayMessage("Oops! An error has occurred. " + ex.Message);
    ErrorTracking.SaveError(user.LoginID, Page.Title, "btnLogin_Click", ex);
}
    }
}

using System;

using System.Collections.Generic;

using System.Net.Http;

using System.Threading.Tasks;

using Newtonsoft.Json;

using System.Net.Http.Headers;

public partial class Login : System.Web.UI.Page

{

protected void Page_Load(object sender, EventArgs e)

{

// No async in Page_Load here, handled in button click

}

protected async void btnLogin_Click(object sender, EventArgs e)

{

string username = txtUsername.Text;

string password = txtPassword.Text;

string apiUrl = "https://yourdomain.com/api/v1/auth/login/"; // Replace with your actual API

try

{

using (HttpClientHandler handler = new HttpClientHandler())

{

handler.UseCookies = true;

handler.CookieContainer = new System.Net.CookieContainer();

using (HttpClient client = new HttpClient(handler))

{

// Set request header explicitly

client.DefaultRequestHeaders.Accept.Clear();

client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/x-www-form-urlencoded"));

var formData = new FormUrlEncodedContent(new[]

{

new KeyValuePair<string, string>("username", username),

new KeyValuePair<string, string>("password", password)

});

// Optional: Manually set the content type header on the content itself (though it's already handled)

formData.Headers.ContentType = new MediaTypeHeaderValue("application/x-www-form-urlencoded");

HttpResponseMessage response = await client.PostAsync(apiUrl, formData);

if (response.IsSuccessStatusCode)

{

Uri uri = new Uri(apiUrl);

var cookies = handler.CookieContainer.GetCookies(uri);

foreach (System.Net.Cookie cookie in cookies)

{

lblResult.Text += $"<br />Cookie: {cookie.Name} = {cookie.Value}";

}

else

{

DisplayMessage("Login failed: " + response.StatusCode);

}

catch (Exception ex)

{

DisplayMessage("Oops! An error has occurred. " + ex.Message);

ErrorTracking.SaveError(user.LoginID, Page.Title, "btnLogin_Click", ex);

}

How to Call Web API from an ASPX Page and Handle the Response

Project Scenario

Prerequisites

Step-by-Step Implementation

Call Web API from an ASPX Page

Leave a Comment X

How to Call Web API from an ASPX Page and Handle the Response

Project Scenario

Prerequisites

Step-by-Step Implementation

Call Web API from an ASPX Page

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Leave a Comment X