Specify `authenticationContext` type

Lib/KeychainAccess/Keychain.swift

@@ -25,6 +25,9 @@
 
 import Foundation
 import Security
+#if os(iOS) || os(OSX)
+import LocalAuthentication
+#endif
 
 public let KeychainAccessErrorDomain = "com.kishikawakatsumi.KeychainAccess.error"
 
@@ -389,11 +392,12 @@ public final class Keychain {
         return options.authenticationPrompt
     }
 
+    #if os(iOS) || os(OSX)
     @available(iOS 9.0, OSX 10.11, *)
-    @available(watchOS, unavailable)
-    public var authenticationContext: Any? {
-        return options.authenticationContext
+    public var authenticationContext: LAContext? {
+        return options.authenticationContext as? LAContext
     }
+    #endif
 
     fileprivate let options: Options
 
@@ -495,13 +499,14 @@ public final class Keychain {
         return Keychain(options)
     }
 
+    #if os(iOS) || os(OSX)
     @available(iOS 9.0, OSX 10.11, *)
-    @available(watchOS, unavailable)
-    public func authenticationContext(_ authenticationContext: Any) -> Keychain {
+    public func authenticationContext(_ authenticationContext: LAContext) -> Keychain {
         var options = self.options
         options.authenticationContext = authenticationContext
         return Keychain(options)
     }
+    #endif
 
     // MARK:
 
@@ -1064,7 +1069,7 @@ struct Options {
     var comment: String?
 
     var authenticationPrompt: String?
-    var authenticationContext: Any?
+    var authenticationContext: AnyObject?
 
     var attributes = [String: Any]()
 }
@@ -1201,7 +1206,7 @@ extension Options {
             }
         }
 
-        #if os(iOS) || os(macOS)
+        #if !os(watchOS)
         if #available(iOS 9.0, OSX 10.11, *) {
             if authenticationContext != nil {
                 query[UseAuthenticationContext] = authenticationContext