initial commit: Proximity iOS app proposal, full Swift code scaffold, reference backend, testing docs, generated Xcode project

Proximity/Services/Auth/KeychainStore.swift

@@ -0,0 +1,47 @@
+import Foundation
+import Security
+
+/// Secure persistence for the session token using the iOS Keychain.
+/// Never stores the session in UserDefaults or plain files.
+struct KeychainStore {
+
+    private let service = "com.proximity.app.session"
+
+    func save(_ session: Session) {
+        let data = (try? JSONEncoder().encode(session)) ?? Data()
+        let query: [String: Any] = [
+            kSecClass as String: kSecClassGenericPassword,
+            kSecAttrService as String: service,
+            kSecAttrAccount as String: "session"
+        ]
+        // Delete existing, then add.
+        SecItemDelete(query as CFDictionary)
+        var add = query
+        add[kSecValueData as String] = data
+        SecItemAdd(add as CFDictionary, nil)
+    }
+
+    func loadSession() -> Session? {
+        let query: [String: Any] = [
+            kSecClass as String: kSecClassGenericPassword,
+            kSecAttrService as String: service,
+            kSecAttrAccount as String: "session",
+            kSecReturnData as String: true,
+            kSecMatchLimit as String: kSecMatchLimitOne
+        ]
+        var result: AnyObject?
+        let status = SecItemCopyMatching(query as CFDictionary, &result)
+        guard status == errSecSuccess,
+              let data = result as? Data else { return nil }
+        return try? JSONDecoder().decode(Session.self, from: data)
+    }
+
+    func clearSession() {
+        let query: [String: Any] = [
+            kSecClass as String: kSecClassGenericPassword,
+            kSecAttrService as String: service,
+            kSecAttrAccount as String: "session"
+        ]
+        SecItemDelete(query as CFDictionary)
+    }
+}