feat(sdk): ✨ Add username/password authentication matching existing client

Implemented dynamic token authentication using existing RetrieveToken pattern:

## Authentication Enhancements:
- **UsernamePasswordProvider**: Implements existing `POST /api/v1/login` flow
- **Token Caching**: 1-hour cache with thread-safe refresh logic
- **NewClientWithCredentials()**: Convenience constructor for username/password auth
- **Dual Auth Support**: Both static token and dynamic username/password flows

## Key Features:
- **Exact API Match**: Mirrors existing `client/client.go RetrieveToken()` implementation
- **Thread Safety**: Concurrent token refresh with mutex protection
- **Caching Strategy**: Reduces login calls, configurable expiry
- **Error Handling**: Structured login failures with context
- **Token Invalidation**: Manual cache clearing for token refresh

## Implementation Details:
```go
// Static token (existing)
client := client.NewClient(baseURL,
  client.WithAuthProvider(client.NewStaticTokenProvider(token)))

// Username/password (new - matches existing pattern)
client := client.NewClientWithCredentials(baseURL, username, password)
```

## Testing:
- **Comprehensive Auth Tests**: Login success/failure, caching, expiry
- **Mock Server Tests**: httptest-based token flow validation
- **Concurrent Safety**: Token refresh under concurrent access
- **Updated Examples**: Support both auth methods

## Backward Compatibility:
- Existing StaticTokenProvider unchanged
- All existing APIs maintain same signatures
- Example updated to support both auth methods via environment variables

This matches the existing prototype's authentication exactly while adding
production features like caching and thread safety.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

sdk/examples/deploy_app.go

@@ -16,20 +16,34 @@ import (
 
 func main() {
 	// Configure SDK client
-	baseURL := getEnvOrDefault("EDGEXR_BASE_URL", "https://hub.apps.edge.platform.mg3.mdb.osc.live/api/v1")
+	baseURL := getEnvOrDefault("EDGEXR_BASE_URL", "https://hub.apps.edge.platform.mg3.mdb.osc.live")
+
+	// Support both token-based and username/password authentication
 	token := getEnvOrDefault("EDGEXR_TOKEN", "")
+	username := getEnvOrDefault("EDGEXR_USERNAME", "")
+	password := getEnvOrDefault("EDGEXR_PASSWORD", "")
 
-	if token == "" {
-		log.Fatal("EDGEXR_TOKEN environment variable is required")
+	var edgeClient *client.Client
+
+	if token != "" {
+		// Use static token authentication
+		fmt.Println("🔐 Using Bearer token authentication")
+		edgeClient = client.NewClient(baseURL,
+			client.WithHTTPClient(&http.Client{Timeout: 30 * time.Second}),
+			client.WithAuthProvider(client.NewStaticTokenProvider(token)),
+			client.WithLogger(log.Default()),
+		)
+	} else if username != "" && password != "" {
+		// Use username/password authentication (matches existing client pattern)
+		fmt.Println("🔐 Using username/password authentication")
+		edgeClient = client.NewClientWithCredentials(baseURL, username, password,
+			client.WithHTTPClient(&http.Client{Timeout: 30 * time.Second}),
+			client.WithLogger(log.Default()),
+		)
+	} else {
+		log.Fatal("Authentication required: Set either EDGEXR_TOKEN or both EDGEXR_USERNAME and EDGEXR_PASSWORD")
 	}
 
-	// Create SDK client with authentication and logging
-	client := client.NewClient(baseURL,
-		client.WithHTTPClient(&http.Client{Timeout: 30 * time.Second}),
-		client.WithAuthProvider(client.NewStaticTokenProvider(token)),
-		client.WithLogger(log.Default()),
-	)
-
 	ctx := context.Background()
 
 	// Example application to deploy
@@ -49,14 +63,14 @@ func main() {
 	}
 
 	// Demonstrate app lifecycle
-	if err := demonstrateAppLifecycle(ctx, client, app); err != nil {
+	if err := demonstrateAppLifecycle(ctx, edgeClient, app); err != nil {
 		log.Fatalf("App lifecycle demonstration failed: %v", err)
 	}
 
 	fmt.Println("✅ SDK example completed successfully!")
 }
 
-func demonstrateAppLifecycle(ctx context.Context, c *client.Client, input *client.NewAppInput) error {
+func demonstrateAppLifecycle(ctx context.Context, edgeClient *client.Client, input *client.NewAppInput) error {
 	appKey := input.App.Key
 	region := input.Region
 
@@ -65,14 +79,14 @@ func demonstrateAppLifecycle(ctx context.Context, c *client.Client, input *clien
 
 	// Step 1: Create the application
 	fmt.Println("\n1. Creating application...")
-	if err := c.CreateApp(ctx, input); err != nil {
+	if err := edgeClient.CreateApp(ctx, input); err != nil {
 		return fmt.Errorf("failed to create app: %w", err)
 	}
 	fmt.Printf("✅ App created: %s/%s v%s\n", appKey.Organization, appKey.Name, appKey.Version)
 
 	// Step 2: Query the application
 	fmt.Println("\n2. Querying application...")
-	app, err := c.ShowApp(ctx, appKey, region)
+	app, err := edgeClient.ShowApp(ctx, appKey, region)
 	if err != nil {
 		return fmt.Errorf("failed to show app: %w", err)
 	}
@@ -82,7 +96,7 @@ func demonstrateAppLifecycle(ctx context.Context, c *client.Client, input *clien
 	// Step 3: List applications in the organization
 	fmt.Println("\n3. Listing applications...")
 	filter := client.AppKey{Organization: appKey.Organization}
-	apps, err := c.ShowApps(ctx, filter, region)
+	apps, err := edgeClient.ShowApps(ctx, filter, region)
 	if err != nil {
 		return fmt.Errorf("failed to list apps: %w", err)
 	}
@@ -90,14 +104,14 @@ func demonstrateAppLifecycle(ctx context.Context, c *client.Client, input *clien
 
 	// Step 4: Clean up - delete the application
 	fmt.Println("\n4. Cleaning up...")
-	if err := c.DeleteApp(ctx, appKey, region); err != nil {
+	if err := edgeClient.DeleteApp(ctx, appKey, region); err != nil {
 		return fmt.Errorf("failed to delete app: %w", err)
 	}
 	fmt.Printf("✅ App deleted: %s/%s v%s\n", appKey.Organization, appKey.Name, appKey.Version)
 
 	// Step 5: Verify deletion
 	fmt.Println("\n5. Verifying deletion...")
-	_, err = c.ShowApp(ctx, appKey, region)
+	_, err = edgeClient.ShowApp(ctx, appKey, region)
 	if err != nil {
 		if fmt.Sprintf("%v", err) == client.ErrResourceNotFound.Error() {
 			fmt.Printf("✅ App successfully deleted (not found)\n")