public class MyRequestParameters : RequestParameters { public bool Pretty { get => Q<bool>("pretty"); init => Q("pretty", value); } } 

using Elastic.Transport; var body = """ { "name": "my-api-key", "expiration": "1d", "...": "..." } """; MyRequestParameters requestParameters = new() { Pretty = true }; var pathAndQuery = requestParameters.CreatePathWithQueryStrings("/_security/api_key", client.ElasticsearchClientSettings); var endpointPath = new EndpointPath(Elastic.Transport.HttpMethod.POST, pathAndQuery); // Or, if the path does not contain query parameters: // new EndpointPath(Elastic.Transport.HttpMethod.POST, "my_path") var response = await client.Transport .RequestAsync<StringResponse>( endpointPath, PostData.String(body), null, null, cancellationToken: default) .ConfigureAwait(false); 

var settings = new ElasticsearchClientSettings(new Uri("http://localhost:9200)) .OnBeforeRequest(OnBeforeRequest); RequestConfiguration? globalRequestConfiguration = null; ConditionalWeakTable<RequestConfiguration, RequestConfiguration>? globalRequestConfigurations = null; void OnBeforeRequest(ElasticsearchClient client, Request request, EndpointPath endpointPath, ref PostData? postData, ref IRequestConfiguration? requestConfiguration) { // Each time a request is made, the transport creates a new `BoundConfiguration` for every `IRequestConfiguration` // that is not in the cache (based on reference equality). // To prevent frequent allocations of our mutated request configurations (and the secondary allocations for // `BoundConfiguration`), we have to maintain a custom cache that maps every original request configuration to the // mutated one. if (requestConfiguration is null) { globalRequestConfiguration = Interlocked.CompareExchange( ref globalRequestConfiguration, new RequestConfiguration { UserAgent = UserAgent.Create("my-custom-user-agent") }, null) ?? globalRequestConfiguration; requestConfiguration = globalRequestConfiguration; return; } if (requestConfiguration is not RequestConfiguration rc) { // Only `RequestConfiguration` (not all implementations of `IRequestConfiguration`) gets cached in the // internal cache. requestConfiguration = MutateRequestConfiguration(requestConfiguration); return; } // ReSharper disable InconsistentlySynchronizedField var cache = (Interlocked.CompareExchange( ref globalRequestConfigurations, new ConditionalWeakTable<RequestConfiguration, RequestConfiguration>(), null ) ?? globalRequestConfigurations); if (cache.TryGetValue(rc, out var mutatedRequestConfiguration)) { requestConfiguration = mutatedRequestConfiguration; return; } mutatedRequestConfiguration = MutateRequestConfiguration(rc); #if NET8_0_OR_GREATER cache.TryAdd(rc, mutatedRequestConfiguration); #else lock (cache) { cache.Add(rc, mutatedRequestConfiguration); } #endif // ReSharper restore InconsistentlySynchronizedField return; RequestConfiguration MutateRequestConfiguration(IRequestConfiguration requestConfiguration) { return new RequestConfiguration(requestConfiguration) { UserAgent = UserAgent.Create("my-custom-user-agent") }; } }