Add support for create token endpoint

Src/Notion.Client/Api/ApiEndpoints.cs

@@ -131,5 +131,10 @@ public static string Create()
                 return "/v1/comments";
             }
         }
+
+        public static class AuthenticationUrls
+        {
+            public static string CreateToken() => "/v1/oauth/token";
+        }
     }
 }

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

@@ -0,0 +1,12 @@
+namespace Notion.Client
+{
+    public sealed partial class AuthenticationClient : IAuthenticationClient
+    {
+        private readonly IRestClient _client;
+
+        public AuthenticationClient(IRestClient restClient)
+        {
+            _client = restClient;
+        }
+    }
+}

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

@@ -0,0 +1,21 @@
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace Notion.Client
+{
+    public sealed partial class AuthenticationClient
+    {
+        public async Task<CreateTokenResponse> CreateTokenAsync(
+            CreateTokenRequest createTokenRequest,
+            CancellationToken cancellationToken = default)
+        {
+            var body = (ICreateTokenBodyParameters)createTokenRequest;
+
+            return await _client.PostAsync<CreateTokenResponse>(
+                ApiEndpoints.AuthenticationUrls.CreateToken(),
+                body,
+                cancellationToken: cancellationToken
+            );
+        }
+    }
+}

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

@@ -0,0 +1,13 @@
+namespace Notion.Client
+{
+    public class CreateTokenRequest : ICreateTokenBodyParameters
+    {
+        public string GrantType => "authorization_code";
+
+        public string Code { get; set; }
+
+        public string RedirectUri { get; set; }
+
+        public ExternalAccount ExternalAccount { get; set; }
+    }
+}

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

@@ -0,0 +1,22 @@
+using Newtonsoft.Json;
+
+namespace Notion.Client
+{
+    /// <summary>
+    /// External account info
+    /// </summary>
+    public class ExternalAccount
+    {
+        /// <summary>
+        /// External account key
+        /// </summary>
+        [JsonProperty("key")]
+        public string Key { get; set; }
+
+        /// <summary>
+        /// External account name
+        /// </summary>
+        [JsonProperty("name")]
+        public string Name { get; set; }
+    }
+}

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

@@ -0,0 +1,35 @@
+using Newtonsoft.Json;
+
+namespace Notion.Client
+{
+    public interface ICreateTokenBodyParameters
+    {
+        /// <summary>
+        /// A constant string: "authorization_code".
+        /// </summary>
+        [JsonProperty("grant_type")]
+        string GrantType { get; }
+
+        /// <summary>
+        /// A unique random code that Notion generates to authenticate with your service,
+        /// generated when a user initiates the OAuth flow.
+        /// </summary>
+        [JsonProperty("code")]
+        string Code { get; set; }
+
+        /// <summary>
+        /// The "redirect_uri" that was provided in the OAuth Domain & URI section
+        /// of the integration's Authorization settings. Do not include this field if a
+        /// "redirect_uri" query param was not included in the Authorization URL
+        /// provided to users. In most cases, this field is required.
+        /// </summary>
+        [JsonProperty("redirect_uri")]
+        string RedirectUri { get; set; }
+
+        /// <summary>
+        /// External account details
+        /// </summary>
+        [JsonProperty("external_account")]
+        ExternalAccount ExternalAccount { get; set; }
+    }
+}

Src/Notion.Client/Api/Authentication/CreateToken/Response/CreateTokenResponse.cs

@@ -0,0 +1,31 @@
+using Newtonsoft.Json;
+
+namespace Notion.Client
+{
+    public class CreateTokenResponse
+    {
+        [JsonProperty("access_token")]
+        public string AccessToken { get; set; }
+
+        [JsonProperty("token_type")]
+        public string TokenType { get; set; } = "bearer";
+
+        [JsonProperty("bot_id")]
+        public string BotId { get; set; }
+
+        [JsonProperty("duplicated_template_id")]
+        public string DuplicatedTemplateId { get; set; }
+
+        [JsonProperty("owner")]
+        public IBotOwner Owner { get; set; }
+
+        [JsonProperty("workspace_icon")]
+        public string WorkspaceIcon { get; set; }
+
+        [JsonProperty("workspace_id")]
+        public string WorkspaceId { get; set; }
+
+        [JsonProperty("workspace_name")]
+        public string WorkspaceName { get; set; }
+    }
+}

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

@@ -0,0 +1,22 @@
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace Notion.Client
+{
+    /// <summary>
+    /// Authentication client
+    /// </summary>
+    public interface IAuthenticationClient
+    {
+        /// <summary>
+        /// Creates an access token that a third-party service can use to authenticate with Notion.
+        /// </summary>
+        /// <param name="createTokenRequest"></param>
+        /// <param name="cancellationToken"></param>
+        /// <returns></returns>
+        Task<CreateTokenResponse> CreateTokenAsync(
+            CreateTokenRequest createTokenRequest,
+            CancellationToken cancellationToken = default
+        );
+    }
+}

Src/Notion.Client/NotionClient.cs

@@ -5,6 +5,8 @@ namespace Notion.Client
     [SuppressMessage("ReSharper", "UnusedMemberInSuper.Global")]
     public interface INotionClient
     {
+        IAuthenticationClient AuthenticationClient { get; }
+
         IUsersClient Users { get; }
 
         IDatabasesClient Databases { get; }
@@ -29,7 +31,8 @@ public NotionClient(
             IPagesClient pages,
             ISearchClient search,
             ICommentsClient comments,
-            IBlocksClient blocks)
+            IBlocksClient blocks,
+            IAuthenticationClient authenticationClient)
         {
             RestClient = restClient;
             Users = users;
@@ -38,8 +41,11 @@ public NotionClient(
             Search = search;
             Comments = comments;
             Blocks = blocks;
+            AuthenticationClient = authenticationClient;
         }
 
+        public IAuthenticationClient AuthenticationClient { get; }
+
         public IUsersClient Users { get; }
 
         public IDatabasesClient Databases { get; }

Src/Notion.Client/NotionClientFactory.cs

@@ -12,8 +12,9 @@ public static NotionClient Create(ClientOptions options)
                 , new DatabasesClient(restClient)
                 , new PagesClient(restClient)
                 , new SearchClient(restClient)
-                , blocks: new BlocksClient(restClient)
-                , comments: new CommentsClient(restClient)
+                , new CommentsClient(restClient)
+                , new BlocksClient(restClient)
+                , new AuthenticationClient(restClient)
             );
         }
     }