Product license verification in Console (#518)

Operator UI - Provide and store License key
- New License section in Operator UI will allow user to provide the
  license key via input form
- New License section in Operator UI will allow the user to fetch the
  license key using subnet credentials
-  Console backend has to verify provided license is valid -
   https://godoc.org/github.com/minio/minio/pkg/licverifier#example-package
-  Console backend has to store the license key in k8s secrets

Operator UI - Set license to tenant during provisioning
- Check if license key exists in k8s secret during tenant creation
- If License is present attach the license-key jwt to the new console
tenant via an environment variable

Operator UI - Set license for an existing tenant
- Tenant view will display information about the current status of the
  Tenant License
- If Tenant doesn't have a License then Operator-UI will allow to attach
new license by clicking the Add License button
- Console backend will extract the license from the k8s secret and save
the license-key jwt in the tenant console environment variable and
redeploy

pkg/subnet/config.go

@@ -0,0 +1,51 @@
+// This file is part of MinIO Kubernetes Cloud
+// Copyright (c) 2020 MinIO, Inc.
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package subnet
+
+import (
+	"errors"
+	"log"
+
+	"github.com/minio/minio/pkg/env"
+	"github.com/minio/minio/pkg/licverifier"
+)
+
+// GetSubnetURL
+func GetSubnetURL() string {
+	return env.Get(ConsoleSubnetURL, "https://subnet.min.io")
+}
+
+// GetLicenseInfoFromJWT will return license metadata from a jwt string license
+func GetLicenseInfoFromJWT(license string, publicKeys []string) (*licverifier.LicenseInfo, error) {
+	if license == "" {
+		return nil, errors.New("license is not present")
+	}
+	for _, publicKey := range publicKeys {
+		lv, err := licverifier.NewLicenseVerifier([]byte(publicKey))
+		if err != nil {
+			log.Print(err)
+			continue
+		}
+		licInfo, err := lv.Verify(license)
+		if err != nil {
+			log.Print(err)
+			continue
+		}
+		return &licInfo, nil
+	}
+	return nil, errors.New("invalid license key")
+}