Add GrpcWeb middleware

Co-authored-by: Kevin Pollet <pollet.kevin@gmail.com>

pkg/middlewares/grpcweb/grpcweb.go

@@ -0,0 +1,27 @@
+package grpcweb
+
+import (
+	"context"
+	"net/http"
+
+	"github.com/improbable-eng/grpc-web/go/grpcweb"
+	"github.com/traefik/traefik/v2/pkg/config/dynamic"
+	"github.com/traefik/traefik/v2/pkg/log"
+	"github.com/traefik/traefik/v2/pkg/middlewares"
+)
+
+const typeName = "grpc-web"
+
+// New builds a new gRPC web request converter.
+func New(ctx context.Context, next http.Handler, config dynamic.GrpcWeb, name string) http.Handler {
+	log.FromContext(middlewares.GetLoggerCtx(ctx, name, typeName)).Debug("Creating middleware")
+
+	return grpcweb.WrapHandler(next, grpcweb.WithCorsForRegisteredEndpointsOnly(false), grpcweb.WithOriginFunc(func(origin string) bool {
+		for _, originCfg := range config.AllowOrigins {
+			if originCfg == "*" || originCfg == origin {
+				return true
+			}
+		}
+		return false
+	}))
+}