Fix: add a support to pass basic authentication for authentication endpoint

Src/Notion.Client/Api/Authentication/CreateToken/AuthenticationClient.cs

@@ -9,11 +9,13 @@ public async Task<CreateTokenResponse> CreateTokenAsync(
             CreateTokenRequest createTokenRequest,
             CancellationToken cancellationToken = default)
         {
-            var body = (ICreateTokenBodyParameters)createTokenRequest;
+            ICreateTokenBodyParameters body = createTokenRequest;
+            IBasicAuthenticationParameters basicAuth = createTokenRequest;
 
             return await _client.PostAsync<CreateTokenResponse>(
                 ApiEndpoints.AuthenticationUrls.CreateToken(),
                 body,
+                basicAuthenticationParameters: basicAuth,
                 cancellationToken: cancellationToken
             );
         }

Src/Notion.Client/Api/Authentication/CreateToken/Request/CreateTokenRequest.cs

@@ -1,6 +1,6 @@
 namespace Notion.Client
 {
-    public class CreateTokenRequest : ICreateTokenBodyParameters
+    public class CreateTokenRequest : ICreateTokenBodyParameters, IBasicAuthenticationParameters
     {
         public string GrantType => "authorization_code";
 
@@ -9,5 +9,9 @@ public class CreateTokenRequest : ICreateTokenBodyParameters
         public string RedirectUri { get; set; }
 
         public ExternalAccount ExternalAccount { get; set; }
+
+        public string ClientId { get; set; }
+
+        public string ClientSecret { get; set; }
     }
 }

Src/Notion.Client/Api/Authentication/HeaderHelpers.cs

@@ -0,0 +1,21 @@
+using System;
+using System.Text;
+
+namespace Notion.Client
+{
+    internal static class HeaderHelpers
+    {
+        public static string GetBasicAuthHeaderValue(IBasicAuthenticationParameters basicAuth)
+        {
+            if (basicAuth == null)
+            {
+                return null;
+            }
+
+            var basicAuthString = $"{basicAuth.ClientId}:{basicAuth.ClientSecret}";
+            var basicAuthHeaderValue = Convert.ToBase64String(Encoding.UTF8.GetBytes(basicAuthString));
+
+            return basicAuthHeaderValue;
+        }
+    }
+}

Src/Notion.Client/Api/Authentication/IBasicAuthenticationParameters.cs

@@ -0,0 +1,8 @@
+namespace Notion.Client
+{
+    public interface IBasicAuthenticationParameters
+    {
+        string ClientId { get; }
+        string ClientSecret { get; }
+    }
+}

Src/Notion.Client/Api/Authentication/RevokeToken/AuthenticationClient.cs

@@ -9,11 +9,13 @@ public async Task RevokeTokenAsync(
             RevokeTokenRequest revokeTokenRequest,
             CancellationToken cancellationToken = default)
         {
-            var body = (IRevokeTokenBodyParameters)revokeTokenRequest;
+            IRevokeTokenBodyParameters body = revokeTokenRequest;
+            IBasicAuthenticationParameters basicAuth = revokeTokenRequest;
 
             await _client.PostAsync<RevokeTokenResponse>(
                 ApiEndpoints.AuthenticationUrls.RevokeToken(),
                 body,
+                basicAuthenticationParameters: basicAuth,
                 cancellationToken: cancellationToken
             );
         }

Src/Notion.Client/Api/Authentication/RevokeToken/Request/RevokeTokenRequest.cs

@@ -1,7 +1,11 @@
 namespace Notion.Client
 {
-    public class RevokeTokenRequest : IRevokeTokenBodyParameters
+    public class RevokeTokenRequest : IRevokeTokenBodyParameters, IBasicAuthenticationParameters
     {
         public string Token { get; set; }
+
+        public string ClientId { get; set; }
+
+        public string ClientSecret { get; set; }
     }
 }

Src/Notion.Client/RestClient/IRestClient.cs

@@ -20,6 +20,7 @@ Task<T> PostAsync<T>(
             IEnumerable<KeyValuePair<string, string>> queryParams = null,
             IDictionary<string, string> headers = null,
             JsonSerializerSettings serializerSettings = null,
+            IBasicAuthenticationParameters basicAuthenticationParameters = null,
             CancellationToken cancellationToken = default);
 
         Task<T> PatchAsync<T>(

Src/Notion.Client/RestClient/RestClient.cs

@@ -48,6 +48,7 @@ public async Task<T> PostAsync<T>(
             IEnumerable<KeyValuePair<string, string>> queryParams = null,
             IDictionary<string, string> headers = null,
             JsonSerializerSettings serializerSettings = null,
+            IBasicAuthenticationParameters basicAuthenticationParameters = null,
             CancellationToken cancellationToken = default)
         {
             void AttachContent(HttpRequestMessage httpRequest)
@@ -56,8 +57,15 @@ void AttachContent(HttpRequestMessage httpRequest)
                     Encoding.UTF8, "application/json");
             }
 
-            var response = await SendAsync(uri, HttpMethod.Post, queryParams, headers, AttachContent,
-                cancellationToken);
+            var response = await SendAsync(
+                uri,
+                HttpMethod.Post,
+                queryParams,
+                headers,
+                AttachContent,
+                basicAuthenticationParameters,
+                cancellationToken
+            );
 
             return await response.ParseStreamAsync<T>(serializerSettings);
         }
@@ -77,7 +85,7 @@ void AttachContent(HttpRequestMessage httpRequest)
             }
 
             var response = await SendAsync(uri, new HttpMethod("PATCH"), queryParams, headers, AttachContent,
-                cancellationToken);
+                basicAuthenticationParameters: null, cancellationToken);
 
             return await response.ParseStreamAsync<T>(serializerSettings);
         }
@@ -88,7 +96,8 @@ public async Task DeleteAsync(
             IDictionary<string, string> headers = null,
             CancellationToken cancellationToken = default)
         {
-            await SendAsync(uri, HttpMethod.Delete, queryParams, headers, null, cancellationToken);
+            await SendAsync(uri, HttpMethod.Delete, queryParams, headers, null,
+                basicAuthenticationParameters: null, cancellationToken);
         }
 
         private static ClientOptions MergeOptions(ClientOptions options)
@@ -116,6 +125,7 @@ private static async Task<Exception> BuildException(HttpResponseMessage response
                     if (errorResponse.ErrorCode == NotionAPIErrorCode.RateLimited)
                     {
                         var retryAfter = response.Headers.RetryAfter.Delta;
+
                         return new NotionApiRateLimitException(
                             response.StatusCode,
                             errorResponse.ErrorCode,
@@ -139,14 +149,16 @@ private async Task<HttpResponseMessage> SendAsync(
             IEnumerable<KeyValuePair<string, string>> queryParams = null,
             IDictionary<string, string> headers = null,
             Action<HttpRequestMessage> attachContent = null,
+            IBasicAuthenticationParameters basicAuthenticationParameters = null,
             CancellationToken cancellationToken = default)
         {
             EnsureHttpClient();
 
             requestUri = AddQueryString(requestUri, queryParams);
 
             using var httpRequest = new HttpRequestMessage(httpMethod, requestUri);
-            httpRequest.Headers.Authorization = new AuthenticationHeaderValue("Bearer", _options.AuthToken);
+
+            httpRequest.Headers.Authorization = CreateAuthenticationHeader(basicAuthenticationParameters);
             httpRequest.Headers.Add("Notion-Version", _options.NotionVersion);
 
             if (headers != null)
@@ -166,6 +178,13 @@ private async Task<HttpResponseMessage> SendAsync(
             return response;
         }
 
+        private AuthenticationHeaderValue CreateAuthenticationHeader(IBasicAuthenticationParameters basicAuth)
+        {
+            return basicAuth != null
+                ? new AuthenticationHeaderValue("Basic", HeaderHelpers.GetBasicAuthHeaderValue(basicAuth))
+                : new AuthenticationHeaderValue("Bearer", _options.AuthToken);
+        }
+
         private static void AddHeaders(HttpRequestMessage request, IDictionary<string, string> headers)
         {
             foreach (var header in headers)

Test/Notion.IntegrationTests/AuthenticationClientTests.cs

@@ -0,0 +1,39 @@
+using System.Threading.Tasks;
+using Notion.Client;
+using Xunit;
+
+namespace Notion.IntegrationTests;
+
+public class AuthenticationClientTests : IntegrationTestBase
+{
+    private readonly string _clientId = GetEnvironmentVariableRequired("NOTION_CLIENT_ID");
+    private readonly string _clientSecret = GetEnvironmentVariableRequired("NOTION_CLIENT_SECRET");
+
+    [Fact]
+    public async Task Create_and_revoke_token()
+    {
+        // Arrange
+        var createRequest = new CreateTokenRequest
+        {
+            Code = "03b3bd2d-6b96-4104-a9f4-ee04d881532c",
+            ClientId = _clientId,
+            ClientSecret = _clientSecret,
+            RedirectUri = "https://localhost:5001",
+        };
+
+        // Act
+        var response = await Client.AuthenticationClient.CreateTokenAsync(createRequest);
+
+        // Assert
+        Assert.NotNull(response);
+        Assert.NotNull(response.AccessToken);
+
+        // revoke token
+        await Client.AuthenticationClient.RevokeTokenAsync(new RevokeTokenRequest
+        {
+            Token = response.AccessToken,
+            ClientId = _clientId,
+            ClientSecret = _clientSecret
+        });
+    }
+}

Test/Notion.IntegrationTests/IntegrationTestBase.cs

@@ -15,10 +15,13 @@ protected IntegrationTestBase()
 
         Client = NotionClientFactory.Create(options);
 
-        ParentPageId = Environment.GetEnvironmentVariable("NOTION_PARENT_PAGE_ID")
-                       ?? throw new InvalidOperationException("Parent page id is required.");
-
-        ParentDatabaseId = Environment.GetEnvironmentVariable("NOTION_PARENT_DATABASE_ID")
-                           ?? throw new InvalidOperationException("Parent database id is required.");
+        ParentPageId = GetEnvironmentVariableRequired("NOTION_PARENT_PAGE_ID");
+        ParentDatabaseId = GetEnvironmentVariableRequired("NOTION_PARENT_DATABASE_ID");
+    }
+
+    protected static string GetEnvironmentVariableRequired(string envName)
+    {
+        return Environment.GetEnvironmentVariable(envName) ??
+               throw new InvalidOperationException($"Environment variable '{envName}' is required.");
     }
 }