Add licverifier package (#10237)

license verification package implements a simple library to 
verify MinIO Subnet license keys.

pkg/licverifier/verifier.go

@@ -0,0 +1,72 @@
+/*
+ * MinIO Cloud Storage, (C) 2020 MinIO, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+// Package licverifier implements a simple library to verify MinIO Subnet license keys.
+package licverifier
+
+import (
+	"crypto/ecdsa"
+	"errors"
+	"fmt"
+
+	"github.com/dgrijalva/jwt-go"
+)
+
+// LicenseVerifier needs an ECDSA public key in PEM format for initialization.
+type LicenseVerifier struct {
+	ecPubKey *ecdsa.PublicKey
+}
+
+// LicenseInfo holds customer metadata present in the license key.
+type LicenseInfo struct {
+	Email           string `json:"sub"`         // Email of the license key requestor
+	TeamName        string `json:"teamName"`    // Subnet team name
+	AccountID       int64  `json:"accountId"`   // Subnet account id
+	StorageCapacity int64  `json:"capacity"`    // Storage capacity used in TB
+	ServiceType     string `json:"serviceType"` // Subnet service type
+}
+
+// Valid checks if customer metadata from the license key is valid.
+func (li *LicenseInfo) Valid() error {
+	if li.AccountID <= 0 {
+		return errors.New("Invalid accountId in claims")
+	}
+	return nil
+}
+
+// NewLicenseVerifier returns an initialized license verifier with the given
+// ECDSA public key in PEM format.
+func NewLicenseVerifier(pemBytes []byte) (*LicenseVerifier, error) {
+	pbKey, err := jwt.ParseECPublicKeyFromPEM(pemBytes)
+	if err != nil {
+		return nil, fmt.Errorf("Failed to parse public key: %s", err)
+	}
+	return &LicenseVerifier{
+		ecPubKey: pbKey,
+	}, nil
+}
+
+// Verify verifies the license key and validates the claims present in it.
+func (lv *LicenseVerifier) Verify(license string) (LicenseInfo, error) {
+	var licInfo LicenseInfo
+	_, err := jwt.ParseWithClaims(license, &licInfo, func(token *jwt.Token) (interface{}, error) {
+		return lv.ecPubKey, nil
+	})
+	if err != nil {
+		return LicenseInfo{}, fmt.Errorf("Failed to verify license: %s", err)
+	}
+	return licInfo, nil
+}