LogUserAgentMiddleware.cs

public class LogUserAgentMiddleware : IMiddleware
{
    private readonly ILogger _logger;

    public LogUserAgentMiddleware(ILogger<LogUserAgentMiddleware> logger)
    {
        // The null check here is belt and braces in case there is a
        // custom middleware factory that uses GetService instead of
        // GetRequiredService. If using the default, this check is not
        // required.
         _logger = logger ?? throw new ArgumentNullException(nameof(logger));
    }
    public async Task InvokeAsync(HttpContext context, RequestDelegate next)
    {
        var userAgent = context.Request.Headers.GetCommaSeparatedValues("User-Agent").LastOrDefault();
        if (userAgent is not null) _logger?.LogTrace($"User Agent : {userAgent}");
        await next(context);
    }
}