refactor vault configuration and add master-key KMS (#6488)

This refactors the vault configuration by moving the
vault-related environment variables to `environment.go`
(Other ENV should follow in the future to have a central
place for adding / handling ENV instead of magic constants
and handling across different files)

Further this commit adds master-key SSE-S3 support.
The operator can specify a SSE-S3 master key using
`MINIO_SSE_MASTER_KEY` which will be used as master key
to derive and encrypt per-object keys for SSE-S3
requests.

This commit is also a pre-condition for SSE-S3
auto-encyption support.

Fixes #6329

cmd/environment.go

@@ -0,0 +1,166 @@
+// Minio Cloud Storage, (C) 2016, 2017, 2018 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 (
+	"encoding/hex"
+	"errors"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+
+	"github.com/minio/minio/cmd/crypto"
+)
+
+const (
+	// EnvKMSMasterKey is the environment variable used to specify
+	// a KMS master key used to protect SSE-S3 per-object keys.
+	// Valid values must be of the from: "KEY_ID:32_BYTE_HEX_VALUE".
+	EnvKMSMasterKey = "MINIO_SSE_MASTER_KEY"
+)
+
+const (
+	// EnvVaultEndpoint is the environment variable used to specify
+	// the vault HTTPS endpoint.
+	EnvVaultEndpoint = "MINIO_SSE_VAULT_ENDPOINT"
+
+	// EnvVaultAuthType is the environment variable used to specify
+	// the authentication type for vault.
+	EnvVaultAuthType = "MINIO_SSE_VAULT_AUTH_TYPE"
+
+	// EnvVaultAppRoleID is the environment variable used to specify
+	// the vault AppRole ID.
+	EnvVaultAppRoleID = "MINIO_SSE_VAULT_APPROLE_ID"
+
+	// EnvVaultAppSecretID is the environment variable used to specify
+	// the vault AppRole secret corresponding to the AppRole ID.
+	EnvVaultAppSecretID = "MINIO_SSE_VAULT_APPROLE_SECRET"
+
+	// EnvVaultKeyVersion is the environment variable used to specify
+	// the vault key version.
+	EnvVaultKeyVersion = "MINIO_SSE_VAULT_KEY_VERSION"
+
+	// EnvVaultKeyName is the environment variable used to specify
+	// the vault named key-ring. In the S3 context it's referred as
+	// customer master key ID (CMK-ID).
+	EnvVaultKeyName = "MINIO_SSE_VAULT_KEY_NAME"
+
+	// EnvVaultCAPath is the environment variable used to specify the
+	// path to a directory of PEM-encoded CA cert files. These CA cert
+	// files are used to authenticate Minio to Vault over mTLS.
+	EnvVaultCAPath = "MINIO_SSE_VAULT_CAPATH"
+
+	// EnvVaultNamespace is the environment variable used to specify
+	// vault namespace. The vault namespace is used if the enterprise
+	// version of Hashicorp Vault is used.
+	EnvVaultNamespace = "MINIO_SSE_VAULT_NAMESPACE"
+)
+
+// Environment provides functions for accessing environment
+// variables.
+var Environment = environment{}
+
+type environment struct{}
+
+// Get retrieves the value of the environment variable named
+// by the key. If the variable is present in the environment the
+// value (which may be empty) is returned. Otherwise it returns
+// the specified default value.
+func (environment) Get(key, defaultValue string) string {
+	if v, ok := os.LookupEnv(key); ok {
+		return v
+	}
+	return defaultValue
+}
+
+// Lookup retrieves the value of the environment variable named
+// by the key. If the variable is present in the environment the
+// value (which may be empty) is returned and the boolean is true.
+// Otherwise the returned value will be empty and the boolean will
+// be false.
+func (environment) Lookup(key string) (string, bool) { return os.LookupEnv(key) }
+
+// LookupKMSConfig extracts the KMS configuration provided by environment
+// variables and merge them with the provided KMS configuration. The
+// merging follows the following rules:
+//
+// 1. A valid value provided as environment variable is higher prioritized
+// than the provided configuration and overwrites the value from the
+// configuration file.
+//
+// 2. A value specified as environment variable never changes the configuration
+// file. So it is never made a persistent setting.
+//
+// It sets the global KMS configuration according to the merged configuration
+// on success.
+func (env environment) LookupKMSConfig(config crypto.KMSConfig) (err error) {
+	// Lookup Hashicorp-Vault configuration & overwrite config entry if ENV var is present
+	config.Vault.Endpoint = env.Get(EnvVaultEndpoint, config.Vault.Endpoint)
+	config.Vault.CAPath = env.Get(EnvVaultCAPath, config.Vault.CAPath)
+	config.Vault.Auth.Type = env.Get(EnvVaultAuthType, config.Vault.Auth.Type)
+	config.Vault.Auth.AppRole.ID = env.Get(EnvVaultAppRoleID, config.Vault.Auth.AppRole.ID)
+	config.Vault.Auth.AppRole.Secret = env.Get(EnvVaultAppSecretID, config.Vault.Auth.AppRole.Secret)
+	config.Vault.Key.Name = env.Get(EnvVaultKeyName, config.Vault.Key.Name)
+	config.Vault.Namespace = env.Get(EnvVaultNamespace, config.Vault.Namespace)
+	keyVersion := env.Get(EnvVaultKeyVersion, strconv.Itoa(config.Vault.Key.Version))
+	config.Vault.Key.Version, err = strconv.Atoi(keyVersion)
+	if err != nil {
+		return fmt.Errorf("Invalid ENV variable: Unable to parse %s value (`%s`)", EnvVaultKeyVersion, keyVersion)
+	}
+	if err = config.Vault.Verify(); err != nil {
+		return err
+	}
+
+	// Lookup KMS master keys - only available through ENV.
+	if masterKey, ok := env.Lookup(EnvKMSMasterKey); ok {
+		if !config.Vault.IsEmpty() { // Vault and KMS master key provided
+			return errors.New("Ambiguous KMS configuration: vault configuration and a master key are provided at the same time")
+		}
+		globalKMSKeyID, globalKMS, err = parseKMSMasterKey(masterKey)
+		if err != nil {
+			return err
+		}
+	}
+	if !config.Vault.IsEmpty() {
+		globalKMS, err = crypto.NewVault(config.Vault)
+		if err != nil {
+			return err
+		}
+		globalKMSKeyID = config.Vault.Key.Name
+	}
+	return nil
+}
+
+// parseKMSMasterKey parses the value of the environment variable
+// `EnvKMSMasterKey` and returns a key-ID and a master-key KMS on success.
+func parseKMSMasterKey(envArg string) (string, crypto.KMS, error) {
+	values := strings.SplitN(envArg, ":", 2)
+	if len(values) != 2 {
+		return "", nil, fmt.Errorf("Invalid KMS master key: %s does not contain a ':'", envArg)
+	}
+	var (
+		keyID  = values[0]
+		hexKey = values[1]
+	)
+	if len(hexKey) != 64 { // 2 hex bytes = 1 byte
+		return "", nil, fmt.Errorf("Invalid KMS master key: %s not a 32 bytes long HEX value", hexKey)
+	}
+	var masterKey [32]byte
+	if _, err := hex.Decode(masterKey[:], []byte(hexKey)); err != nil {
+		return "", nil, fmt.Errorf("Invalid KMS master key: %s not a 32 bytes long HEX value", hexKey)
+	}
+	return keyID, crypto.NewKMS(masterKey), nil
+}