Add Google login suppot (OAuth).

app/src/main/java/chat/rocket/android/authentication/login/presentation/LoginPresenter.kt

@@ -23,6 +23,7 @@ private const val TYPE_LOGIN_USER_EMAIL = 0
 private const val TYPE_LOGIN_CAS = 1
 private const val TYPE_LOGIN_OAUTH = 2
 private const val SERVICE_NAME_GITHUB = "github"
+private const val SERVICE_NAME_GOOGLE = "google"
 private const val SERVICE_NAME_GILAB = "gitlab"
 
 class LoginPresenter @Inject constructor(private val view: LoginView,
@@ -126,8 +127,12 @@ class LoginPresenter @Inject constructor(private val view: LoginView,
                         }
                     }
                     if (settings.isGoogleAuthenticationEnabled()) {
-                        view.enableLoginByGoogle()
-                        totalSocialAccountsEnabled++
+                        val clientId = getOauthClientId(services, SERVICE_NAME_GOOGLE)
+                        if (clientId != null) {
+                            view.setupGoogleButtonListener(UrlHelper.getGoogleOauthUrl(clientId, server!!, state), state)
+                            view.enableLoginByGoogle()
+                            totalSocialAccountsEnabled++
+                        }
                     }
                     if (settings.isLinkedinAuthenticationEnabled()) {
                         view.enableLoginByLinkedin()

app/src/main/java/chat/rocket/android/authentication/login/presentation/LoginView.kt

@@ -117,9 +117,19 @@ interface LoginView : LoadingView, MessageView, InternetView {
 
     /**
      * Shows the "login by Google" view if it is enable by the server settings.
+     *
+     * REMARK: We must set up the Google button listener before enabling it [setupGoogleButtonListener].
      */
     fun enableLoginByGoogle()
 
+    /**
+     * Setups the Google button when tapped.
+     *
+     * @param googleUrl The Google OAuth URL to authenticate with.
+     * @param state A random string generated by the app, which you'll verify later (to protect against forgery attacks).
+     */
+    fun setupGoogleButtonListener(googleUrl: String, state: String)
+
     /**
      * Shows the "login by Linkedin" view if it is enable by the server settings.
      */

app/src/main/java/chat/rocket/android/authentication/login/ui/LoginFragment.kt

@@ -219,6 +219,14 @@ class LoginFragment : Fragment(), LoginView {
         button_google.isClickable = true
     }
 
+    // TODO: Use custom tabs instead of web view. See https://github.com/RocketChat/Rocket.Chat.Android/issues/968
+    override fun setupGoogleButtonListener(googleUrl: String, state: String) {
+        button_google.setOnClickListener {
+            startActivityForResult(context?.oauthWebViewIntent(googleUrl, state), REQUEST_CODE_FOR_OAUTH)
+            activity?.overridePendingTransition(R.anim.slide_up, R.anim.hold)
+        }
+    }
+
     override fun enableLoginByLinkedin() {
         button_linkedin.isClickable = true
     }

app/src/main/java/chat/rocket/android/helper/UrlHelper.kt

@@ -32,9 +32,20 @@ object UrlHelper {
      * @param state An unguessable random string used to protect against forgery attacks.
      * @return The Github Oauth URL.
      */
-    // TODO: Fix github url.
     fun getGithubOauthUrl(clientId: String, state: String): String =
         "https://github.com/login/oauth/authorize?scope=user:email&client_id=$clientId&state=$state"
+
+    /**
+     * Returns the Google Oauth URL.
+     *
+     * @param clientId The Google client ID.
+     * @param serverUrl The server URL.
+     * @param state An unguessable random string used to protect against forgery attacks.
+     * @return The Google Oauth URL.
+     */
+    fun getGoogleOauthUrl(clientId: String, serverUrl: String, state: String) =
+        "https://accounts.google.com/o/oauth2/v2/auth?client_id=$clientId&redirect_uri=${removeTrailingSlash(serverUrl)}/_oauth/google?close&response_type=code&state=$state&scope=email%20profile"
+
     /**
      * Returns the Gitlab Oauth URL.
      *

app/src/main/java/chat/rocket/android/webview/oauth/ui/OauthWebViewActivity.kt

@@ -34,6 +34,8 @@ const val INTENT_OAUTH_CREDENTIAL_SECRET = "credential_secret"
 class OauthWebViewActivity : AppCompatActivity() {
     private lateinit var webPageUrl: String
     private lateinit var state: String
+    private var isWebViewSetUp: Boolean = false
+
 
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
@@ -50,7 +52,10 @@ class OauthWebViewActivity : AppCompatActivity() {
 
     override fun onResume() {
         super.onResume()
-        setupWebView()
+        if (!isWebViewSetUp) {
+            setupWebView()
+            isWebViewSetUp = true
+        }
     }
 
     override fun onBackPressed() {
@@ -69,7 +74,10 @@ class OauthWebViewActivity : AppCompatActivity() {
 
     @SuppressLint("SetJavaScriptEnabled")
     private fun setupWebView() {
-        web_view.settings.javaScriptEnabled = true
+        val settings = web_view.settings
+        settings.javaScriptEnabled = true
+        // TODO This is required to make Google OAuth work, but we shoud use Custom Tabs instead. See https://github.com/RocketChat/Rocket.Chat.Android/issues/968
+        settings.userAgentString = "Mozilla/5.0 (Linux; Android 4.1.1; Galaxy Nexus Build/JRO03C) AppleWebKit/535.19 (KHTML, like Gecko) Chrome/18.0.1025.166 Mobile Safari/535.19"
         web_view.webViewClient = object : WebViewClient() {
             override fun onPageFinished(view: WebView, url: String) {
                 if (url.contains(JSON_CREDENTIAL_TOKEN) && url.contains(JSON_CREDENTIAL_SECRET)) {