New AccountManager component, update samples apps to use it

This introduces an account manager component, and updates two sample apps
to use it - logins and history sync.

AccountManager encapsulates state transitions exposed by Rust liblogins,
and provides a simple observable API and a few public methods to interact
with a FirefoxAccount.

Internally it's implemented as a state machine. Consumers are expected to
handle interactions with a web view that are necessary to complete an OAUTH flow.

components/service/firefox-accounts/build.gradle

@@ -31,9 +31,13 @@ dependencies {
     // Parts of this dependency are typealiase'd or are otherwise part of this module's public API.
     api Dependencies.mozilla_fxa
 
+    // Observable is part of public API of the FxaAccountManager.
+    api project(':support-base')
+
     implementation Dependencies.kotlin_stdlib
     implementation Dependencies.kotlin_coroutines
 
+    testImplementation project(':support-test')
     testImplementation Dependencies.testing_junit
     testImplementation Dependencies.testing_robolectric
     testImplementation Dependencies.testing_mockito

components/service/firefox-accounts/src/main/java/mozilla/components/service/fxa/AccountStorage.kt

@@ -0,0 +1,49 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+package mozilla.components.service.fxa
+
+import android.content.Context
+import android.content.SharedPreferences
+
+const val FXA_STATE_PREFS_KEY = "fxaAppState"
+const val FXA_STATE_KEY = "fxaState"
+
+interface AccountStorage {
+    @Throws(Exception::class)
+    fun read(): FirefoxAccountShaped?
+    fun write(account: FirefoxAccountShaped)
+    fun clear()
+}
+
+class SharedPrefAccountStorage(val context: Context) : AccountStorage {
+    /**
+     * @throws FxaException if JSON failed to parse into a [FirefoxAccount].
+     */
+    override fun read(): FirefoxAccountShaped? {
+        val savedJSON = accountPreferences().getString(FXA_STATE_KEY, null)
+                ?: return null
+
+        // May throw a generic FxaException if it fails to process saved JSON.
+        return FirefoxAccount.fromJSONString(savedJSON)
+    }
+
+    override fun write(account: FirefoxAccountShaped) {
+        accountPreferences()
+            .edit()
+            .putString(FXA_STATE_KEY, account.toJSONString())
+            .apply()
+    }
+
+    override fun clear() {
+        accountPreferences()
+            .edit()
+            .remove(FXA_STATE_KEY)
+            .apply()
+    }
+
+    private fun accountPreferences(): SharedPreferences {
+        return context.getSharedPreferences(FXA_STATE_PREFS_KEY, Context.MODE_PRIVATE)
+    }
+}

components/service/firefox-accounts/src/main/java/mozilla/components/service/fxa/FirefoxAccount.kt

@@ -16,15 +16,21 @@ import org.mozilla.fxaclient.internal.FxaException.Unauthorized as Unauthorized
 /**
  * Facilitates testing consumers of FirefoxAccount.
  */
-interface FirefoxAccountShaped {
+interface FirefoxAccountShaped : AutoCloseable {
+    fun beginOAuthFlow(scopes: Array<String>, wantsKeys: Boolean): Deferred<String>
+    fun beginPairingFlow(pairingUrl: String, scopes: Array<String>): Deferred<String>
+    fun getProfile(ignoreCache: Boolean): Deferred<Profile>
+    fun getProfile(): Deferred<Profile>
+    fun completeOAuthFlow(code: String, state: String): Deferred<Unit>
     fun getAccessToken(singleScope: String): Deferred<AccessTokenInfo>
     fun getTokenServerEndpointURL(): String
+    fun toJSONString(): String
 }
 
 /**
  * FirefoxAccount represents the authentication state of a client.
  */
-class FirefoxAccount internal constructor(private val inner: InternalFxAcct) : AutoCloseable, FirefoxAccountShaped {
+class FirefoxAccount internal constructor(private val inner: InternalFxAcct) : FirefoxAccountShaped {
 
     private val job = SupervisorJob()
     private val scope = CoroutineScope(Dispatchers.IO) + job
@@ -50,11 +56,11 @@ class FirefoxAccount internal constructor(private val inner: InternalFxAcct) : A
      * @param wantsKeys Fetch keys for end-to-end encryption of data from Mozilla-hosted services
      * @return Deferred<String> that resolves to the flow URL when complete
      */
-    fun beginOAuthFlow(scopes: Array<String>, wantsKeys: Boolean): Deferred<String> {
+    override fun beginOAuthFlow(scopes: Array<String>, wantsKeys: Boolean): Deferred<String> {
         return scope.async { inner.beginOAuthFlow(scopes, wantsKeys) }
     }
 
-    fun beginPairingFlow(pairingUrl: String, scopes: Array<String>): Deferred<String> {
+    override fun beginPairingFlow(pairingUrl: String, scopes: Array<String>): Deferred<String> {
         return scope.async { inner.beginPairingFlow(pairingUrl, scopes) }
     }
 
@@ -67,7 +73,7 @@ class FirefoxAccount internal constructor(private val inner: InternalFxAcct) : A
      * @throws Unauthorized We couldn't find any suitable access token to make that call.
      * The caller should then start the OAuth Flow again with the "profile" scope.
      */
-    fun getProfile(ignoreCache: Boolean): Deferred<Profile> {
+    override fun getProfile(ignoreCache: Boolean): Deferred<Profile> {
         return scope.async {
             val internalProfile = inner.getProfile(ignoreCache)
             Profile(
@@ -87,7 +93,7 @@ class FirefoxAccount internal constructor(private val inner: InternalFxAcct) : A
      * @throws Unauthorized We couldn't find any suitable access token to make that call.
      * The caller should then start the OAuth Flow again with the "profile" scope.
      */
-    fun getProfile(): Deferred<Profile> = getProfile(false)
+    override fun getProfile(): Deferred<Profile> = getProfile(false)
 
     /**
      * Fetches the token server endpoint, for authentication using the SAML bearer flow.
@@ -109,7 +115,7 @@ class FirefoxAccount internal constructor(private val inner: InternalFxAcct) : A
      *
      * Modifies the FirefoxAccount state.
      */
-    fun completeOAuthFlow(code: String, state: String): Deferred<Unit> {
+    override fun completeOAuthFlow(code: String, state: String): Deferred<Unit> {
         return scope.async { inner.completeOAuthFlow(code, state) }
     }
 
@@ -135,7 +141,7 @@ class FirefoxAccount internal constructor(private val inner: InternalFxAcct) : A
      *
      * @return String containing the authentication details in JSON format
      */
-    fun toJSONString(): String = inner.toJSONString()
+    override fun toJSONString(): String = inner.toJSONString()
 
     companion object {
         /**