How do you use the HttpContext object in Blazor server-side to retrieve information about the user or user agent?

Use HttpContext through the IHttpContextAccessor interface to get the user agent details in a Blazor Server application. The following example demonstrates how to use HttpContext to get the user agent and IP address details by default. Extend the AddHttpContextAccessor() method in the Program.cs file. 

[Program.cs]

builder.Services.AddHttpContextAccessor();

[Index.razor]

@page "/"
@using Microsoft.AspNetCore.Http
@inject IHttpContextAccessor httpContextAccessor

<p>UserAgent = @UserAgent</p>
<p>IPAddress = @IPAddress</p>

@code {
    public string UserAgent { get; set; }
    public string IPAddress { get; set; }

    protected override void OnInitialized()
    {
        UserAgent = httpContextAccessor.HttpContext.Request.Headers["User-Agent"];
        IPAddress = httpContextAccessor.HttpContext.Connection.RemoteIpAddress.ToString();
    }
}

Refer to this link for more details.