Suggestion for adding Retrofit support to API with minimal impact on …

…existing solution:

* Only change to Client.kt is to make it override a ClientInterface
* Added RetrofitClientFacade to wrap normal client, that add Retrofit service support
* Retrofit service will be built when calling resumeLastLoggedInUser() RetrofitClientFacade
* All other client calls to RetrofitClientFacade will by proxied to the normal Client instance
* For Retrofit clients, makeAuthenticatedRequest() should be caused on RetrofitClientFacade instance and not on User object

webflows/src/main/kotlin/com/schibsted/account/webflows/client/Client.kt

@@ -83,7 +83,7 @@ sealed class RefreshTokenError {
 typealias LoginResultHandler = (Either<LoginError, User>) -> Unit
 
 /**  Represents a client registered with Schibsted account. */
-class Client {
+class Client : ClientInterface {
     internal val httpClient: OkHttpClient
     internal val schibstedAccountApi: SchibstedAccountApi
     internal val configuration: ClientConfiguration
@@ -133,7 +133,7 @@ class Client {
      * @param authRequest Authentication request parameters.
      */
     @JvmOverloads
-    fun getAuthenticationIntent(context: Context, authRequest: AuthRequest = AuthRequest()): Intent {
+    override fun getAuthenticationIntent(context: Context, authRequest: AuthRequest): Intent {
         val customTabsIntent = CustomTabsIntent.Builder().build().apply {
             intent.data = generateLoginUrl(authRequest)
         }
@@ -146,7 +146,7 @@ class Client {
      * @param authRequest Authentication request parameters.
      */
     @JvmOverloads
-    fun launchAuth(context: Context, authRequest: AuthRequest = AuthRequest()) {
+    override fun launchAuth(context: Context, authRequest: AuthRequest) {
         CustomTabsIntent.Builder()
             .build()
             .launchUrl(context, generateLoginUrl(authRequest))
@@ -164,7 +164,7 @@ class Client {
      * This only needs to be used if manually starting the login flow using [launchAuth].
      * If using [getAuthenticationIntent] this step will be handled for you.
      */
-    fun handleAuthenticationResponse(intent: Intent, callback: LoginResultHandler) {
+    override fun handleAuthenticationResponse(intent: Intent, callback: LoginResultHandler) {
         val authResponse = intent.data?.query ?: return callback(
             Left(LoginError.UnexpectedError("No authentication response"))
         )
@@ -223,7 +223,7 @@ class Client {
     }
 
     /** Resume any previously logged-in user session */
-    fun resumeLastLoggedInUser(): User? {
+    override fun resumeLastLoggedInUser(): User? {
         val session = sessionStorage.get(configuration.clientId) ?: return null
         return User(this, session.userTokens)
     }

webflows/src/main/kotlin/com/schibsted/account/webflows/client/ClientInterface.kt

@@ -0,0 +1,35 @@
+package com.schibsted.account.webflows.client
+
+import android.content.Context
+import android.content.Intent
+import com.schibsted.account.webflows.activities.AuthorizationManagementActivity
+import com.schibsted.account.webflows.user.User
+
+interface ClientInterface {
+    /**
+     * Start login flow.
+     *
+     * Requires [AuthorizationManagementActivity.setup] to have been called before this.
+     *
+     * @param authRequest Authentication request parameters.
+     */
+    fun getAuthenticationIntent(context: Context, authRequest: AuthRequest = AuthRequest()): Intent
+
+    /**
+     * Start auth activity manually.
+     *
+     * @param authRequest Authentication request parameters.
+     */
+    fun launchAuth(context: Context, authRequest: AuthRequest = AuthRequest())
+
+    /**
+     * Call this with the intent received via deep link to complete the login flow.
+     *
+     * This only needs to be used if manually starting the login flow using [launchAuth].
+     * If using [getAuthenticationIntent] this step will be handled for you.
+     */
+    fun handleAuthenticationResponse(intent: Intent, callback: LoginResultHandler)
+
+    /** Resume any previously logged-in user session */
+    fun resumeLastLoggedInUser(): User?
+}

webflows/src/main/kotlin/com/schibsted/account/webflows/client/RetrofitClientFacade.kt

@@ -0,0 +1,55 @@
+package com.schibsted.account.webflows.client
+
+import com.schibsted.account.webflows.user.User
+import retrofit2.Retrofit
+
+/**  Represents a client registered with Schibsted account - with Retrofit support. */
+class RetrofitClientFacade<S>(
+    private val client: Client,
+    private val serviceClass: Class<S>,
+    private val retrofitBuilder: Retrofit.Builder,
+): ClientInterface by client {
+
+    private var retrofitApi: S? = null
+    private var user: User? = null
+
+    /** Resume any previously logged-in user session */
+    override fun resumeLastLoggedInUser(): User? {
+        val loggedInUser = client.resumeLastLoggedInUser()
+
+        if (loggedInUser != null) {
+            user = loggedInUser
+            retrofitApi = retrofitBuilder
+                .client(loggedInUser.httpClient)
+                .build()
+                .create(serviceClass)
+
+            return loggedInUser
+        }
+
+        user = null
+        retrofitApi = null
+        return null
+    }
+
+    /**
+     * Perform the given [request] with user access token as Bearer token in Authorization header.
+     *
+     * If the initial request fails with a 401, a refresh token request is made to get a new access
+     * token and the request will be retried with the new token if successful.
+     *
+     * If the refresh token request fails with an OAuth 'invalid_grant' error response, meaning the
+     * refresh token has expired or been invalidated, the user will be logged-out (and all existing
+     * tokens will be destroyed).
+     *
+     * @param request retrofit suspend request to perform with authentication using user tokens
+     */
+    suspend fun <V> makeAuthenticatedRequest(request: suspend (S) -> V?): V? {
+        if (user?.isLoggedIn() == true) {
+            retrofitApi?.let {
+                return request(it)
+            }
+        }
+        return null
+    }
+}