Move LoginHandler into LoginServer which others embed (#3431)

* Move LoginHandler into LoginServer which others embed

* Add unit tests for loginServer

cmd/login-server.go

@@ -0,0 +1,41 @@
+/*
+ * Minio Cloud Storage, (C) 2016 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 cmd
+
+import "time"
+
+type loginServer struct {
+}
+
+// LoginHandler - Handles JWT based RPC logic.
+func (b loginServer) LoginHandler(args *RPCLoginArgs, reply *RPCLoginReply) error {
+	jwt, err := newJWT(defaultInterNodeJWTExpiry, serverConfig.GetCredential())
+	if err != nil {
+		return err
+	}
+	if err = jwt.Authenticate(args.Username, args.Password); err != nil {
+		return err
+	}
+	token, err := jwt.GenerateToken(args.Username)
+	if err != nil {
+		return err
+	}
+	reply.Token = token
+	reply.Timestamp = time.Now().UTC()
+	reply.ServerVersion = Version
+	return nil
+}