feat: add support for OAuth tokens.

src/NLog.Targets.ElasticSearch/ElasticsearchTokenProvider.cs

@@ -0,0 +1,132 @@
+using Newtonsoft.Json;
+using NLog.Common;
+using System;
+using System.Net.Http;
+using System.Net.Http.Headers;
+using System.Text;
+
+namespace NLog.Targets.ElasticSearch
+{
+    public sealed class ElasticsearchTokenProvider : IElasticsearchTokenProvider
+    {
+        private const string DefaultContentType = "application/json";
+        private readonly Uri _baseAddress;
+        private readonly string _username;
+        private readonly string _password;
+
+        public ElasticsearchTokenProvider(Uri baseAddress, string username, string password)
+        {
+            _baseAddress = baseAddress;
+            _password = password;
+            _username = username;
+        }
+
+        public OAuthAccessToken GetToken()
+        {
+            var tokenRequest = new
+            {
+                grant_type = "password",
+                username = _username,
+                password = _password,
+            };
+
+            using var stringContent = new StringContent(
+                JsonConvert.SerializeObject(tokenRequest),
+                Encoding.UTF8,
+                DefaultContentType);
+
+            OAuthAccessToken token = null;
+            try
+            {
+                token = DoRequest<OAuthAccessToken>(stringContent, HttpMethod.Post);
+                if (token != null)
+                {
+                    token.GeneratedTime = DateTime.UtcNow.Ticks;
+                }
+            }
+            catch (Exception ex)
+            {
+                InternalLogger.Error(ex, "ElasticSearch: Error generating the token.");
+            }
+
+            return token;
+        }
+
+        public OAuthAccessToken RefreshToken(OAuthAccessToken currentToken)
+        {
+            var refreshToken = new
+            {
+                grant_type = "refresh_token",
+                refresh_token = currentToken?.RefreshToken,
+            };
+
+            using var stringContent = new StringContent(
+                JsonConvert.SerializeObject(refreshToken),
+                Encoding.UTF8,
+                DefaultContentType);
+
+            OAuthAccessToken token;
+            try
+            {
+                token = DoRequest<OAuthAccessToken>(stringContent, HttpMethod.Post, currentToken?.AccessToken);
+                if (token != null)
+                {
+                    token.GeneratedTime = DateTime.UtcNow.Ticks;
+                }
+            }
+            catch (Exception ex)
+            {
+                InternalLogger.Error(ex, "ElasticSearch: Error refreshing the token. Trying to generate new token.");
+
+                token = GetToken();
+            }
+
+            return token;
+        }
+
+        private T DoRequest<T>(HttpContent content, HttpMethod httpMethod, string bearerToken = null)
+        {
+            using var httpClient = new HttpClient { BaseAddress = _baseAddress };
+            httpClient.DefaultRequestHeaders.Accept.ParseAdd(DefaultContentType);
+            using var request = new HttpRequestMessage
+            {
+                Method = httpMethod,
+                RequestUri = new Uri($"/_security/oauth2/token", UriKind.Relative),
+                Content = content,
+            };
+
+            if (!string.IsNullOrWhiteSpace(bearerToken))
+            {
+                request.Headers.Authorization = new AuthenticationHeaderValue("Bearer", bearerToken);
+            }
+            else
+            {
+                if (!string.IsNullOrWhiteSpace(_username))
+                {
+                    var encodedCredential = Convert.ToBase64String(Encoding.UTF8.GetBytes($"{_username}:{_password}"));
+
+                    request.Headers.Authorization = new AuthenticationHeaderValue("Basic", encodedCredential);
+                }
+                else
+                {
+                    InternalLogger.Error("ElasticSearch: For token generation a username must be configured.");
+                    return default;
+                }
+            }
+
+            using var response = httpClient.SendAsync(request).GetAwaiter().GetResult();
+
+            if (!response.IsSuccessStatusCode)
+            {
+                var responseContent = response.Content.ReadAsStringAsync();
+
+                InternalLogger.Error($"ElasticSearch: error trying to refresh token. Call status: {response.StatusCode}. Response: {responseContent}");
+                return default;
+            }
+
+            var token = JsonConvert.DeserializeObject<T>(response.Content.ReadAsStringAsync().GetAwaiter().GetResult());
+
+            return token;
+        }
+    }
+}

src/NLog.Targets.ElasticSearch/ExceptionExtensions.cs

@@ -7,7 +7,9 @@ internal static class ExceptionExtensions
         public static Exception FlattenToActualException(this Exception exception)
         {
             if (!(exception is AggregateException aggregateException))
+            {
                 return exception;
+            }
 
             var flattenException = aggregateException.Flatten();
             if (flattenException.InnerExceptions.Count == 1)

src/NLog.Targets.ElasticSearch/ExpandoObjectExtensions.cs

@@ -1,13 +1,12 @@
 using System.Collections.Generic;
 using System.Dynamic;
-using System.Linq;
 
 namespace NLog.Targets.ElasticSearch
 {
     internal static class ExpandoObjectExtensions
     {
         /// <summary>
-        /// Replaces dot ('.') character in Keys with an underscore ('_') 
+        /// Replaces dot ('.') character in Keys with an underscore ('_')
         /// </summary>
         /// <returns>ExpandoObject</returns>
         public static ExpandoObject ReplaceDotInKeys(this ExpandoObject obj, bool alwaysCloneObject = true)
@@ -19,15 +18,21 @@ public static ExpandoObject ReplaceDotInKeys(this ExpandoObject obj, bool always
                 {
                     case null:
                         if (clone == null)
+                        {
                             return obj.ReplaceDotInKeys();
+                        }
+
                         break;
                     case ExpandoObject expandoObject:
                         if (clone == null)
+                        {
                             return obj.ReplaceDotInKeys();
+                        }
+
                         ((IDictionary<string, object>)clone)[item.Key.Replace('.', '_')] = expandoObject.ReplaceDotInKeys();
                         break;
                     default:
-                        if (item.Key.Contains('.'))
+                        if (item.Key.Contains("."))
                         {
                             if (clone == null)
                                 return obj.ReplaceDotInKeys();
@@ -37,9 +42,11 @@ public static ExpandoObject ReplaceDotInKeys(this ExpandoObject obj, bool always
                         {
                             ((IDictionary<string, object>)clone)[item.Key] = item.Value;
                         }
+
                         break;
                 }
             }
+
             return clone ?? obj;
         }
     }

src/NLog.Targets.ElasticSearch/Field.cs

@@ -1,6 +1,6 @@
-using System;
-using NLog.Config;
+using NLog.Config;
 using NLog.Layouts;
+using System;
 
 namespace NLog.Targets.ElasticSearch
 {
@@ -20,7 +20,7 @@ public class Field
         /// Value with NLog <see cref="NLog.Layouts.Layout"/> rendering support
         /// </summary>
         [RequiredParameter]
-        public Layout Layout { get; set; } 
+        public Layout Layout { get; set; }
 
         /// <summary>
         /// Custom type conversion from default string to other type

src/NLog.Targets.ElasticSearch/FlatObjectContractResolver.cs

@@ -1,7 +1,7 @@
-using System;
-using System.Reflection;
-using Newtonsoft.Json;
+using Newtonsoft.Json;
 using Newtonsoft.Json.Serialization;
+using System;
+using System.Reflection;
 
 namespace NLog.Targets.ElasticSearch
 {
@@ -16,7 +16,10 @@ protected override JsonProperty CreateProperty(MemberInfo member, MemberSerializ
         {
             var jsonProperty = base.CreateProperty(member, memberSerialization);
             if (jsonProperty.Readable && !IsSimpleType(jsonProperty.PropertyType))
+            {
                 jsonProperty.Converter = _flatObjectConverter;
+            }
+
             return jsonProperty;
         }
 

src/NLog.Targets.ElasticSearch/IElasticSearchTarget.cs

@@ -1,8 +1,8 @@
-using System;
+using Elasticsearch.Net;
+using NLog.Layouts;
+using System;
 using System.Collections.Generic;
 using System.Net;
-using Elasticsearch.Net;
-using NLog.Layouts;
 
 namespace NLog.Targets.ElasticSearch
 {
@@ -13,7 +13,6 @@ public interface IElasticSearchTarget
     {
         /// <summary>
         /// Gets or sets a connection string name to retrieve the Uri from.
-        /// 
         /// Use as an alternative to Uri
         /// </summary>
         string ConnectionStringName { get; set; }
@@ -33,7 +32,7 @@ public interface IElasticSearchTarget
         /// <summary>
         /// Set it to true if ElasticSearch uses BasicAuth
         /// </summary>
-        [Obsolete]
+        [Obsolete("Deprecated. Authentication is done with BasicAuth if field Username is not empty.")]
         bool RequireAuth { get; set; }
 
         /// <summary>

src/NLog.Targets.ElasticSearch/IElasticsearchTokenProvider.cs

@@ -0,0 +1,9 @@
+namespace NLog.Targets.ElasticSearch
+{
+    public interface IElasticsearchTokenProvider
+    {
+        OAuthAccessToken GetToken();
+
+        OAuthAccessToken RefreshToken(OAuthAccessToken currentToken);
+    }
+}

src/NLog.Targets.ElasticSearch/JsonToStringConverter.cs

@@ -1,20 +1,20 @@
-using System;
-using Newtonsoft.Json;
+using Newtonsoft.Json;
+using System;
 
 namespace NLog.Targets.ElasticSearch
 {
     internal sealed class JsonToStringConverter : JsonConverter
     {
         private readonly Type _type;
 
-        /// <inheritdoc />
-        public override bool CanRead { get; } = false;
-
         public JsonToStringConverter(Type type)
         {
             _type = type;
         }
 
+        /// <inheritdoc />
+        public override bool CanRead { get; } = false;
+
         /// <inheritdoc />
         public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
         {

src/NLog.Targets.ElasticSearch/NLog.Targets.ElasticSearch.csproj

@@ -12,12 +12,14 @@
     <DelaySign>false</DelaySign>
     <AssemblyOriginatorKeyFile>NLog.Targets.ElasticSearch.snk</AssemblyOriginatorKeyFile>
     <GenerateDocumentationFile>true</GenerateDocumentationFile>
+    <LangVersion>9</LangVersion>
   </PropertyGroup>
   <ItemGroup>
     <PackageReference Include="Elasticsearch.Net" Version="7.13.2" />
     <PackageReference Include="NEST" Version="7.13.2" />
     <PackageReference Include="Newtonsoft.Json" Version="12.0.3" />
     <PackageReference Include="NLog" Version="4.6.8" />
     <PackageReference Include="Microsoft.SourceLink.GitHub" Version="1.0.0" PrivateAssets="All" />
+    <PackageReference Include="System.Net.Http" Version="4.3.4" />
   </ItemGroup>
 </Project>

src/NLog.Targets.ElasticSearch/OAuthAccessToken.cs

@@ -0,0 +1,54 @@
+using Newtonsoft.Json;
+
+namespace NLog.Targets.ElasticSearch
+{
+    public class OAuthAccessToken
+    {
+        [JsonProperty(PropertyName = "access_token")]
+        public string AccessToken { get; set; }
+
+        [JsonProperty(PropertyName = "expires_in")]
+        public long ExpiresIn { get; set; }
+
+        public string Scope { get; set; }
+
+        public string Type { get; set; }
+
+        [JsonProperty(PropertyName = "refresh_token")]
+        public string RefreshToken { get; set; }
+
+        public long GeneratedTime { get; set; }
+
+        public override int GetHashCode()
+        {
+            unchecked
+            {
+                var hash = 17;
+                hash = (hash * 23) + AccessToken?.GetHashCode() ?? 0;
+                hash = (hash * 23) + RefreshToken?.GetHashCode() ?? 0;
+                return hash;
+            }
+        }
+
+        public override bool Equals(object obj)
+        {
+            if (obj is null)
+            {
+                return false;
+            }
+
+            if (ReferenceEquals(this, obj))
+            {
+                return true;
+            }
+
+            if (obj.GetType() != GetType())
+            {
+                return false;
+            }
+
+            var objTyped = (OAuthAccessToken)obj;
+            return this.AccessToken.Equals(objTyped.AccessToken) && this.RefreshToken.Equals(objTyped.RefreshToken);
+        }
+    }
+}