refactor(credentials): derive RPC secret fallback and remove IAM keygen duplication (#3079)

* refactor(credentials): derive rpc secret and remove iam keygen

* fix(credentials): reject default access key RPC secret

* test(credentials): align RPC fallback and add keygen coverage

crates/credentials/Cargo.toml

@@ -1,3 +1,17 @@
+# Copyright 2024 RustFS Team
+#
+# 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]
 name = "rustfs-credentials"
 edition.workspace = true
@@ -12,9 +26,11 @@ categories = ["web-programming", "development-tools", "data-structures", "securi
 
 [dependencies]
 base64-simd = { workspace = true }
+hmac = { workspace = true }
 rand = { workspace = true }
 serde = { workspace = true }
 serde_json.workspace = true
+sha2 = { workspace = true }
 time = { workspace = true, features = ["serde", "parsing", "formatting", "macros"] }
 
 [lints]