Config migration should handle plain-text (#8506)

This PR fixes issues found in config migration

 - StorageClass migration error when rrs is empty
 - Plain-text migration of older config
 - Do not run in safe mode with incorrect credentials
 - Update logger_http documentation for _STATE env

Refer more reported issues at #8434

cmd/config-encrypted_test.go

@@ -0,0 +1,75 @@
+/*
+ * MinIO Cloud Storage, (C) 2019 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 (
+	"bytes"
+	"testing"
+
+	"github.com/minio/minio/pkg/auth"
+	"github.com/minio/minio/pkg/madmin"
+)
+
+func TestDecryptData(t *testing.T) {
+	cred1 := auth.Credentials{
+		AccessKey: "minio",
+		SecretKey: "minio123",
+	}
+
+	cred2 := auth.Credentials{
+		AccessKey: "minio",
+		SecretKey: "minio1234",
+	}
+
+	data := []byte(`config data`)
+	edata1, err := madmin.EncryptData(cred1.String(), data)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	edata2, err := madmin.EncryptData(cred2.String(), data)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	tests := []struct {
+		edata   []byte
+		creds   []auth.Credentials
+		success bool
+	}{
+		{edata1, []auth.Credentials{cred1, cred2}, true},
+		{edata2, []auth.Credentials{cred1, cred2}, true},
+		{data, []auth.Credentials{cred1, cred2}, false},
+	}
+
+	for _, test := range tests {
+		t.Run("", func(t *testing.T) {
+			ddata, err := decryptData(test.edata, test.creds...)
+			if err != nil && test.success {
+				t.Errorf("Expected success, saw failure %v", err)
+			}
+			if err == nil && !test.success {
+				t.Error("Expected failure, saw success")
+			}
+			if test.success {
+				if !bytes.Equal(ddata, data) {
+					t.Errorf("Expected %s, got %s", string(data), string(ddata))
+				}
+			}
+		})
+	}
+}