Method to check native auth availability for provider in the device

.ruby-version

@@ -1 +1 @@
-ruby-2.2.1
+ruby-2.3.1

.swiftlint.yml

@@ -18,7 +18,7 @@ type_body_length:
   - 400 # error
 type_name:
   min_length: 3 # only warning
-variable_name:
+identifier_name:
   min_length: # only min_length
     warning: 3 # only error
   excluded: # No regex support available for this
@@ -27,4 +27,7 @@ variable_name:
     - a0_isManagementError
     - a0_fragmentValues
     - a0_queryValues
+    - Code
+    - WebLink
+    - AndroidLink
 reporter: "xcode" # reporter type (xcode, json, csv, checkstyle, junit)

Auth0/AuthProvider.swift

@@ -35,8 +35,23 @@ import UIKit
          ...
          return transaction
      }
+
+     static func isAvailable() -> Bool {
+         return true
+     }
+
  ```
  */
 public protocol AuthProvider {
     func login(withConnection connection: String, scope: String, parameters: [String: Any]) -> NativeAuthTransaction
+
+    /**
+     Determine if the Auth method used by the Provider is available on the device.
+     e.g. If using a Twitter Auth provider it should check the presence of a Twitter account on the device.
+
+     If a Auth is performed on a provider that returns `false` the transaction will fail with an error.
+
+     - returns: Bool if the AuthProvider is available on the device
+     */
+    static func isAvailable() -> Bool
 }

Auth0/Handlers.swift

@@ -65,7 +65,7 @@ func databaseUser(from response: Response<AuthenticationError>, callback: Reques
 
 func noBody(from response: Response<AuthenticationError>, callback: Request<Void, AuthenticationError>.Callback) {
     do {
-        let _ = try response.result()
+        _ = try response.result()
         callback(.success(result: ()))
     } catch let error {
         callback(.failure(error: error))

Auth0/SafariSession.swift

@@ -66,7 +66,7 @@ class SafariSession: NSObject, AuthTransaction {
             }
         var items = self.handler.values(fromComponents: components)
         guard has(state: self.state, inItems: items) else { return false }
-        if let _ = items["error"] {
+        if items["error"] != nil {
             self.finish(.failure(error: AuthenticationError(info: items, statusCode: 0)))
         } else {
             self.handler.credentials(from: items, callback: self.finish)

Auth0/_ObjectiveWebAuth.swift

@@ -39,7 +39,7 @@ public class _ObjectiveOAuth2: NSObject {
     }
 
     public func addParameters(_ parameters: [String: String]) {
-        let _ = self.webAuth.parameters(parameters)
+        _ = self.webAuth.parameters(parameters)
     }
 
     /**
@@ -64,7 +64,7 @@ public class _ObjectiveOAuth2: NSObject {
     public var connection: String? {
         set {
             if let value = newValue {
-                let _ = self.webAuth.connection(value)
+                _ = self.webAuth.connection(value)
             }
         }
         get {
@@ -78,7 +78,7 @@ public class _ObjectiveOAuth2: NSObject {
     public var scope: String? {
         set {
             if let value = newValue {
-                let _ = self.webAuth.scope(value)
+                _ = self.webAuth.scope(value)
             }
         }
         get {