feat: plugins integration.

pkg/server/middleware/middlewares.go

@@ -28,6 +28,7 @@ import (
 	"github.com/containous/traefik/v2/pkg/middlewares/stripprefix"
 	"github.com/containous/traefik/v2/pkg/middlewares/stripprefixregex"
 	"github.com/containous/traefik/v2/pkg/middlewares/tracing"
+	"github.com/containous/traefik/v2/pkg/plugins"
 	"github.com/containous/traefik/v2/pkg/server/provider"
 )
 
@@ -40,6 +41,7 @@ const (
 // Builder the middleware builder.
 type Builder struct {
 	configs        map[string]*runtime.MiddlewareInfo
+	pluginBuilder  *plugins.Builder
 	serviceBuilder serviceBuilder
 }
 
@@ -48,8 +50,8 @@ type serviceBuilder interface {
 }
 
 // NewBuilder creates a new Builder.
-func NewBuilder(configs map[string]*runtime.MiddlewareInfo, serviceBuilder serviceBuilder) *Builder {
-	return &Builder{configs: configs, serviceBuilder: serviceBuilder}
+func NewBuilder(configs map[string]*runtime.MiddlewareInfo, serviceBuilder serviceBuilder, pluginBuilder *plugins.Builder) *Builder {
+	return &Builder{configs: configs, serviceBuilder: serviceBuilder, pluginBuilder: pluginBuilder}
 }
 
 // BuildChain creates a middleware chain.
@@ -338,6 +340,27 @@ func (b *Builder) buildConstructor(ctx context.Context, middlewareName string) (
 		}
 	}
 
+	// Plugin
+	if config.Plugin != nil {
+		if middleware != nil {
+			return nil, badConf
+		}
+
+		pluginType, rawPluginConfig, err := findPluginConfig(config.Plugin)
+		if err != nil {
+			return nil, err
+		}
+
+		m, err := b.pluginBuilder.Build(pluginType, rawPluginConfig, middlewareName)
+		if err != nil {
+			return nil, err
+		}
+
+		middleware = func(next http.Handler) (http.Handler, error) {
+			return m.NewHandler(ctx, next)
+		}
+	}
+
 	if middleware == nil {
 		return nil, fmt.Errorf("invalid middleware %q configuration: invalid middleware type or middleware does not exist", middlewareName)
 	}