add Package.swift file to support integration with Swift Package Manager (#237) (#243)

Co-authored-by: Luke Newman <[email protected]>

Author: IldarAbdullin-okta

Package.swift

@@ -0,0 +1,18 @@
+// swift-tools-version:5.1
+// The swift-tools-version declares the minimum version of Swift required to build this package.
+
+import PackageDescription
+
+let package = Package(
+    name: "OktaOidc",
+    platforms: [
+        .macOS(.v10_10), .iOS(.v11)
+    ],
+    products: [
+        .library(name: "OktaOidc", targets: ["OktaOidc"])
+    ],
+    targets: [
+        .target(name: "OktaOidc", dependencies: []),
+        .testTarget(name: "OktaTests", dependencies: ["OktaOidc"])
+    ]
+)