Addressed unwanted logout when opening app

When there are asynchronous API calls, such as when the app starts,
the token refresh would be called twice resulting in unhandled 401
responses. Logic to retry the request has been added, and the
authenticator is now synchronized.

VideoLocker/src/main/java/org/edx/mobile/http/OauthRefreshTokenAuthenticator.java

@@ -2,6 +2,7 @@
 
 import android.content.Context;
 import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 
 import com.google.inject.Inject;
 import com.jakewharton.retrofit.Ok3Client;
@@ -36,6 +37,8 @@ public class OauthRefreshTokenAuthenticator implements Authenticator {
 
     private final Logger logger = new Logger(getClass().getName());
     private final static String TOKEN_EXPIRED_ERROR_MESSAGE = "token_expired";
+    private final static String TOKEN_NONEXISTENT_ERROR_MESSAGE = "token_nonexistent";
+    private final static String TOKEN_INVALID_GRANT_ERROR_MESSAGE = "invalid_grant";
     private Context context;
 
     @Inject
@@ -44,32 +47,49 @@ public class OauthRefreshTokenAuthenticator implements Authenticator {
     @Inject
     LoginPrefs loginPrefs;
 
+
     public OauthRefreshTokenAuthenticator(Context context) {
         this.context = context;
         RoboGuice.injectMembers(context, this);
     }
 
     @Override
-    public Request authenticate(Route route, final Response response) throws IOException {
+    public synchronized Request authenticate(Route route, final Response response) throws IOException {
         logger.warn(response.toString());
 
-        if (!isTokenExpired(response.peekBody(200).string())) {
-            return null;
-        }
-
         final AuthResponse currentAuth = loginPrefs.getCurrentAuth();
         if (null == currentAuth || null == currentAuth.refresh_token) {
             return null;
         }
-        final AuthResponse refreshedAuth;
-        try {
-            refreshedAuth = refreshAccessToken(currentAuth);
-        } catch (HttpException e) {
-            return null;
+
+        String errorCode = getErrorCode(response.peekBody(200).string());
+
+        if (errorCode != null) {
+            switch (errorCode) {
+                case TOKEN_EXPIRED_ERROR_MESSAGE:
+                    final AuthResponse refreshedAuth;
+                    try {
+                        refreshedAuth = refreshAccessToken(currentAuth);
+                    } catch (HttpException e) {
+                        return null;
+                    }
+                    return response.request().newBuilder()
+                            .header("Authorization", refreshedAuth.token_type + " " + refreshedAuth.access_token)
+                            .build();
+                case TOKEN_NONEXISTENT_ERROR_MESSAGE:
+                case TOKEN_INVALID_GRANT_ERROR_MESSAGE:
+                    // Retry request with the current access_token if the original access_token used in
+                    // request does not match the current access_token. This case can occur when
+                    // asynchronous calls are made and are attempting to refresh the access_token where
+                    // one call succeeds but the other fails. https://github.com/edx/edx-app-android/pull/834
+                    if (!response.request().headers().get("Authorization").split(" ")[1].equals(currentAuth.access_token)) {
+                        return response.request().newBuilder()
+                                .header("Authorization", currentAuth.token_type + " " + currentAuth.access_token)
+                                .build();
+                    }
+            }
         }
-        return response.request().newBuilder()
-                .header("Authorization", refreshedAuth.token_type + " " + refreshedAuth.access_token)
-                .build();
+        return null;
     }
 
     @NonNull
@@ -88,16 +108,14 @@ private AuthResponse refreshAccessToken(AuthResponse currentAuth) throws HttpExc
         return refreshTokenResponse;
     }
 
-    /**
-     * Checks the if the error_code in the response body is the token_expired error code.
-     */
-    private boolean isTokenExpired(String responseBody) {
+    @Nullable
+    private String getErrorCode(String responseBody) {
         try {
             JSONObject jsonObj = new JSONObject(responseBody);
-            String errorCode = jsonObj.getString("error_code");
-            return errorCode.equals(TOKEN_EXPIRED_ERROR_MESSAGE);
+            return jsonObj.getString("error_code");
         } catch (JSONException ex) {
-            return false;
+            logger.warn("Unable to get error_code from 401 response");
+            return null;
         }
     }
 }