Add client ip to graylog output with Gelf.Extensions.Logging package - asp.net-core

Question

I am using the Gelf.Extensions.Logging package to send log info to graylog from an asp.net core 3 website, and I would like additional fields like current user name, client ip, user agent.
In startup.cs, I have the following, but I don't know how to add the data to AdditionalFields that I want - I'm not even sure that this would be the right place, as I can't see how to inject the http context at this early stage.
public static IHostBuilder CreateHostBuilder(string[] args) =>
Host.CreateDefaultBuilder(args)
.ConfigureWebHostDefaults(webBuilder =>
{
webBuilder.UseStartup<Startup>()
.ConfigureLogging((context, builder) => builder.AddGelf(options =>
{
options.AdditionalFields["machine_name"] = Environment.MachineName;
options.AdditionalFields["environment_name"] = context.HostingEnvironment.EnvironmentName;
options.AdditionalFields["app_version"] = Assembly.GetEntryAssembly()?.GetCustomAttribute<AssemblyInformationalVersionAttribute>().InformationalVersion;
}));
});
My appsettings.json is like so:
{
"Logging": {
"IncludeScopes": false,
"LogLevel": {
"Default": "Information",
"Microsoft": "Information",
"System": "Warning"
},
"GELF": {
"Host": "graylog",
"Port": 12202,
"Protocol": "HTTP",
"LogSource": "DataEntry",
"LogLevel": {
"Default": "Information",
"Microsoft": "Information",
"System": "Warning"
}
}
},
"AllowedHosts": "*",
/* snip */
}

Answer 1

It turns out the recommended approach here it to use a middleware like this example to add information about the current request as fields:
public class Startup
{
public void Configure(IApplicationBuilder app)
{
// Register the middleware like so:
app.UseAppEnvironmentInfo();
}
}
public static class RequestAppEnvironmentInfoMiddlewareExtensions
{
public static IApplicationBuilder UseAppEnvironmentInfo(
this IApplicationBuilder builder)
{
return builder.UseMiddleware<AppEnvironmentInfoMiddleware>();
}
}
public class AppEnvironmentInfoMiddleware
{
private readonly RequestDelegate _next;
private readonly IHttpContextAccessor _httpContextAccessor;
private readonly ILogger<AppEnvironmentInfoMiddleware> _logger;
public AppEnvironmentInfoMiddleware(RequestDelegate next,
IHttpContextAccessor httpContextAccessor, ILogger<AppEnvironmentInfoMiddleware> logger)
{
_next = next;
_httpContextAccessor = httpContextAccessor;
_logger = logger;
}
public async Task Invoke(HttpContext context)
{
using (_logger.BeginScope(("machine_name", Environment.MachineName)))
using (_logger.BeginScope(("environment_name", context.HostingEnvironment.EnvironmentName)))
using (_logger.BeginScope(("app_version", Assembly.GetEntryAssembly()?.GetCustomAttribute<AssemblyInformationalVersionAttribute>().InformationalVersion)))
{
await _next.Invoke(context);
}
}
}