refactor: Restructure project layout and clean up dependencies (#30)

This commit introduces a significant reorganization of the project structure to improve maintainability and clarity.

Key changes include:
- Adjusted the directory layout for a more logical module organization.
- Removed unused crate dependencies, reducing the overall project size and potentially speeding up build times.
- Updated import paths and configuration files to reflect the structural changes.

crates/policy/src/auth.rs

@@ -0,0 +1,47 @@
+// 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.
+
+mod credentials;
+
+pub use credentials::Credentials;
+pub use credentials::*;
+use serde::{Deserialize, Serialize};
+use time::OffsetDateTime;
+
+#[derive(Serialize, Deserialize, Clone, Debug, Default)]
+pub struct UserIdentity {
+    pub version: i64,
+    pub credentials: Credentials,
+    pub update_at: Option<OffsetDateTime>,
+}
+
+impl UserIdentity {
+    pub fn new(credentials: Credentials) -> Self {
+        UserIdentity {
+            version: 1,
+            credentials,
+            update_at: Some(OffsetDateTime::now_utc()),
+        }
+    }
+}
+
+impl From<Credentials> for UserIdentity {
+    fn from(value: Credentials) -> Self {
+        UserIdentity {
+            version: 1,
+            credentials: value,
+            update_at: Some(OffsetDateTime::now_utc()),
+        }
+    }
+}