started stubbing things out

src/Garmin/ApiClient.cs

@@ -14,6 +14,7 @@ namespace Garmin
 	public interface IGarminApiClient
 	{
 		Task InitSigninFlowAsync(object queryParams, string userAgent, out CookieJar jar);
+		Task InitCookieJarAsync(object queryParams, string userAgent, out CookieJar jar)
 		Task<SendCredentialsResult> SendCredentialsAsync(GarminApiAuthentication auth, object queryParams, object loginData, CookieJar jar);
 		Task<string> SendMfaCodeAsync(string userAgent, object queryParams, object mfaData, CookieJar jar);
 		Task<IFlurlResponse> SendServiceTicketAsync(string userAgent, string serviceTicket, CookieJar jar);
@@ -25,6 +26,7 @@ public class ApiClient : IGarminApiClient
 		private const string BASE_URL = "https://connect.garmin.com";
 		private const string SSO_URL = "https://sso.garmin.com";
 		private const string SIGNIN_URL = "https://sso.garmin.com/sso/signin";
+		private const string SSO_EMBED_URL = "https://sso.garmin.com/sso/embed";
 
 		private static string UPLOAD_URL = $"{BASE_URL}/modern/proxy/upload-service/upload";
 
@@ -42,6 +44,16 @@ public Task InitSigninFlowAsync(object queryParams, string userAgent, out Cookie
 						.GetStringAsync();
 		}
 
+		public Task InitCookieJarAsync(object queryParams, string userAgent, out CookieJar jar)
+		{
+			return SSO_EMBED_URL
+						.WithHeader("User-Agent", userAgent)
+						.WithHeader("origin", ORIGIN)
+						.SetQueryParams(queryParams)
+						.WithCookies(out jar)
+						.GetStringAsync();
+		}
+
 		public async Task<SendCredentialsResult> SendCredentialsAsync(GarminApiAuthentication auth, object queryParams, object loginData, CookieJar jar)
 		{
 			var result = new SendCredentialsResult();

src/Garmin/Auth/GarminOAuthService.cs

@@ -1,6 +1,12 @@
-using System;
+using Common.Service;
+using Common.Stateful;
+using Flurl;
+using Flurl.Http;
+using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Net;
+using System.Runtime.Intrinsics.X86;
 using System.Text;
 using System.Threading.Tasks;
 
@@ -11,6 +17,55 @@ public interface IGarminOAuthService
 
 }
 
-public class GarminOAuthService
-{
+public class GarminOAuthService : IGarminOAuthService
+{
+	private readonly ISettingsService _settingsService;
+	private readonly IGarminApiClient _apiClient;
+
+	public GarminOAuthService(ISettingsService settingsService, IGarminApiClient apiClient)
+	{
+		_settingsService = settingsService;
+		_apiClient = apiClient;
+	}
+
+	private async Task GetAuthTokenAsync()
+	{
+		var auth = new GarminApiAuthentication();
+		auth.UserAgent = "Mozilla/5.0 (iPhone; CPU iPhone OS 16_5 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) Mobile/15E148";
+
+
+		/////////////////////////////////
+		// Init Cookie Jar
+		////////////////////////////////
+		var queryParams = new
+		{
+			id = "gauth-widget",
+			embedWidget = "true",
+			gauthHost = "https://sso.garmin.com/sso"
+		};
+
+		CookieJar jar = null;
+		try
+		{
+			await _apiClient.InitCookieJarAsync(queryParams, auth.UserAgent, out jar);
+		}
+		catch (FlurlHttpException e)
+		{
+			throw new GarminAuthenticationError("Failed to initialize sign in flow.", e) { Code = Code.FailedPriorToCredentialsUsed };
+		}
+
+		object loginData = new
+		{
+			embed = "true",
+			username = auth.Email,
+			password = auth.Password,
+			lt = "e1s1",
+			_eventId = "submit",
+			displayNameRequired = "false",
+		};
+
+		/////////////////////////////////
+		// Get CSRF token
+		////////////////////////////////
+	}
 }

src/Garmin/Garmin.csproj

@@ -24,6 +24,10 @@
     <None Remove="Fit\**" />
   </ItemGroup>
 
+  <ItemGroup>
+    <PackageReference Include="IdentityModel" Version="6.2.0" />
+  </ItemGroup>
+
   <ItemGroup>
     <ProjectReference Include="..\Common\Common.csproj" />
   </ItemGroup>