Android refresh method (#314)

* add android refresh function to return accessToken and idToken

* update android refresh token to return accessToken and idToken

* add documentation for Android refresh method

* format android refresh documentation

* delete dead space from android refresh documentation

* add space in android refresh documentation

README.md

@@ -154,6 +154,25 @@ plugin first use `androidClientId` if not found use `clientId` if not found use
 </resources>
 ```
 
+**Refresh method**
+
+This method should be called when the app is initialized to establish if the user is currently logged in. If true, the method will return an accessToken, idToken and an empty refreshToken.
+```ts
+checkLoggedIn() {
+    GoogleAuth.refresh()
+        .then((data) => {
+            if (data.accessToken) {
+                this.currentTokens = data;
+            }
+        })
+        .catch((error) => {
+            if (error.type === 'userLoggedOut') {
+                this.signin()
+            }
+        });
+}
+```
+
 ## Configure
 
 | Name                     | Type     | Description                                                                                                                   |

android/src/main/java/com/codetrixstudio/capacitor/GoogleAuth/GoogleAuth.java

@@ -137,7 +137,23 @@ protected void signInResult(PluginCall call, ActivityResult result) {
 
   @PluginMethod()
   public void refresh(final PluginCall call) {
-    call.reject("I don't know how to refresh token on Android");
+    GoogleSignInAccount account = GoogleSignIn.getLastSignedInAccount(getContext());
+    if (account == null) {
+      call.reject("User not logged in.");
+    } else {
+      try {
+        JSONObject accessTokenObject = getAuthToken(account.getAccount(), true);
+
+        JSObject authentication = new JSObject();
+        authentication.put("idToken", account.getIdToken());
+        authentication.put(FIELD_ACCESS_TOKEN, accessTokenObject.get(FIELD_ACCESS_TOKEN));
+        authentication.put("refreshToken", "");
+        call.resolve(authentication);
+      } catch(Exception e){
+        e.printStackTrace();
+        call.reject("Something went wrong while retrieving access token", e);
+      }
+    }
   }
 
   @PluginMethod()