diff --git a/cmd/garth/main.go b/cmd/garth/main.go
new file mode 100644
index 0000000..0776be7
--- /dev/null
+++ b/cmd/garth/main.go
@@ -0,0 +1,92 @@
+package main
+
+import (
+	"encoding/json"
+	"flag"
+	"fmt"
+	"log"
+	"time"
+
+	"garmin-connect/garth/client"
+	"garmin-connect/garth/credentials"
+	"garmin-connect/garth/types"
+)
+
+func main() {
+	// Parse command line flags
+	outputTokens := flag.Bool("tokens", false, "Output OAuth tokens in JSON format")
+	flag.Parse()
+
+	// Load credentials from .env file
+	email, password, domain, err := credentials.LoadEnvCredentials()
+	if err != nil {
+		log.Fatalf("Failed to load credentials: %v", err)
+	}
+
+	// Create client
+	garminClient, err := client.NewClient(domain)
+	if err != nil {
+		log.Fatalf("Failed to create client: %v", err)
+	}
+
+	// Try to load existing session first
+	sessionFile := "garmin_session.json"
+	if err := garminClient.LoadSession(sessionFile); err != nil {
+		fmt.Println("No existing session found, logging in with credentials from .env...")
+
+		if err := garminClient.Login(email, password); err != nil {
+			log.Fatalf("Login failed: %v", err)
+		}
+
+		// Save session for future use
+		if err := garminClient.SaveSession(sessionFile); err != nil {
+			fmt.Printf("Failed to save session: %v\n", err)
+		}
+	} else {
+		fmt.Println("Loaded existing session")
+	}
+
+	// If tokens flag is set, output tokens and exit
+	if *outputTokens {
+		tokens := struct {
+			OAuth1 *types.OAuth1Token `json:"oauth1"`
+			OAuth2 *types.OAuth2Token `json:"oauth2"`
+		}{
+			OAuth1: garminClient.OAuth1Token,
+			OAuth2: garminClient.OAuth2Token,
+		}
+
+		jsonBytes, err := json.MarshalIndent(tokens, "", "  ")
+		if err != nil {
+			log.Fatalf("Failed to marshal tokens: %v", err)
+		}
+		fmt.Println(string(jsonBytes))
+		return
+	}
+
+	// Test getting activities
+	activities, err := garminClient.GetActivities(5)
+	if err != nil {
+		log.Fatalf("Failed to get activities: %v", err)
+	}
+
+	// Display activities
+	displayActivities(activities)
+}
+
+func displayActivities(activities []types.Activity) {
+	fmt.Printf("\n=== Recent Activities ===\n")
+	for i, activity := range activities {
+		fmt.Printf("%d. %s\n", i+1, activity.ActivityName)
+		fmt.Printf("   Type: %s\n", activity.ActivityType.TypeKey)
+		fmt.Printf("   Date: %s\n", activity.StartTimeLocal)
+		if activity.Distance > 0 {
+			fmt.Printf("   Distance: %.2f km\n", activity.Distance/1000)
+		}
+		if activity.Duration > 0 {
+			duration := time.Duration(activity.Duration) * time.Second
+			fmt.Printf("   Duration: %v\n", duration.Round(time.Second))
+		}
+		fmt.Println()
+	}
+}
diff --git a/garth/client/auth_test.go b/garth/client/auth_test.go
new file mode 100644
index 0000000..a404c1d
--- /dev/null
+++ b/garth/client/auth_test.go
@@ -0,0 +1,57 @@
+package client_test
+
+import (
+	"net/http"
+	"testing"
+
+	"garmin-connect/garth/testutils"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"garmin-connect/garth/client"
+	"garmin-connect/garth/errors"
+)
+
+func TestClient_Login_Success(t *testing.T) {
+	// Create mock SSO server
+	ssoServer := testutils.MockJSONResponse(http.StatusOK, `{
+		"access_token": "test_token",
+		"token_type": "Bearer",
+		"expires_in": 3600
+	}`)
+	defer ssoServer.Close()
+
+	// Create client with test configuration
+	c, err := client.NewClient("example.com")
+	require.NoError(t, err)
+	c.Domain = ssoServer.URL
+
+	// Perform login
+	err = c.Login("test@example.com", "password")
+
+	// Verify login
+	require.NoError(t, err)
+	assert.Equal(t, "Bearer test_token", c.AuthToken)
+}
+
+func TestClient_Login_Failure(t *testing.T) {
+	// Create mock SSO server returning error
+	ssoServer := testutils.MockJSONResponse(http.StatusUnauthorized, `{
+		"error": "invalid_credentials"
+	}`)
+	defer ssoServer.Close()
+
+	// Create client with test configuration
+	c, err := client.NewClient("example.com")
+	require.NoError(t, err)
+	c.Domain = ssoServer.URL
+
+	// Perform login
+	err = c.Login("test@example.com", "wrongpassword")
+
+	// Verify error
+	require.Error(t, err)
+	assert.IsType(t, &errors.AuthenticationError{}, err)
+	assert.Contains(t, err.Error(), "SSO login failed")
+}
diff --git a/garth/client/client_test.go b/garth/client/client_test.go
new file mode 100644
index 0000000..f17a8e6
--- /dev/null
+++ b/garth/client/client_test.go
@@ -0,0 +1,40 @@
+package client_test
+
+import (
+	"net/http"
+	"testing"
+	"time"
+
+	"garmin-connect/garth/testutils"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"garmin-connect/garth/client"
+)
+
+func TestClient_GetUserProfile(t *testing.T) {
+	// Create mock server returning user profile
+	server := testutils.MockJSONResponse(http.StatusOK, `{
+		"userName": "testuser",
+		"displayName": "Test User",
+		"fullName": "Test User",
+		"location": "Test Location"
+	}`)
+	defer server.Close()
+
+	// Create client with test configuration
+	c := &client.Client{
+		Domain:     server.URL,
+		HTTPClient: &http.Client{Timeout: 5 * time.Second},
+		AuthToken:  "Bearer testtoken",
+	}
+
+	// Get user profile
+	profile, err := c.GetUserProfile()
+
+	// Verify response
+	require.NoError(t, err)
+	assert.Equal(t, "testuser", profile.UserName)
+	assert.Equal(t, "Test User", profile.DisplayName)
+}
diff --git a/garth/testutils/http.go b/garth/testutils/http.go
new file mode 100644
index 0000000..3fe9506
--- /dev/null
+++ b/garth/testutils/http.go
@@ -0,0 +1,14 @@
+package testutils
+
+import (
+	"net/http"
+	"net/http/httptest"
+)
+
+func MockJSONResponse(code int, body string) *httptest.Server {
+	return httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		w.WriteHeader(code)
+		w.Write([]byte(body))
+	}))
+}