Improved type safety, local auth support, and better error handling

Sources/KeychainKit/Protocols/KeychainServiceProtocol.swift

@@ -0,0 +1,28 @@
+import Foundation
+
+/// A protocol that defines the required properties for a keychain service descriptor.
+///
+/// Types conforming to this protocol provide an identifier used to distinguish stored items
+/// and may optionally specify an access group to enable keychain sharing between apps.
+public protocol KeychainServiceProtocol {
+    /// A unique string used to identify the keychain service.
+    var identifier: String { get }
+
+    /// An optional keychain access group identifier to support shared access between apps.
+    ///
+    /// The default implementation returns `nil`, indicating no access group is specified.
+    var accessGroup: String? { get }
+}
+
+public extension KeychainServiceProtocol {
+    /// The default implementation returns `nil`, indicating that no access group is specified.
+    var accessGroup: String? { nil }
+}
+
+public extension KeychainServiceProtocol where Self: RawRepresentable, Self.RawValue == String {
+    /// Provides a default `identifier` implementation for `RawRepresentable` types
+    /// whose `RawValue` is `String`.
+    ///
+    /// The `identifier` is derived from the raw string value.
+    var identifier: String { rawValue }
+}