oauth - Invalid credentials: Google API calendar

Question

I am new to using Google APIs. I followed steps to setup Google Calendar sample code in eclipse using Google client library. I deployed the code to app engine using the cmd command- mvn appengine:update (when tried to deploy through eclipse it gave me an error saying the project is not an App Engine project). Deploying through command line worked and I could launch my web application.

Suddenly, after few API request calls, started getting invalid credentials error:

error:401
domain:global
location: authorization
locationtype : header
message: invalid credentials
reason: auth error

I searched this error and found it may occur if your auth token is invalid or expired. I am not sure what I need to do to get a new auth token. In my case, there is a client_secrets.json file which has the client secrets. I did not put/save or use the auth token anywhere in the code. Following is what I remember when I deployed the code for the first time:

• There was some token which I was asked to paste on the cmd as I was deploying using the command line. After that I could launch my application.
• After that whenever I deployed my code and launched the application, there was no authorization(which happened the first time) and I could use the application and the API subsequently.
• Suddenly I started getting invalid credentials error.

I was using client_secrets.json generated from the developer's console and I did not provide auth token anywhere in the code and I did not save it either. I read that a refresh token can be used and that can avoid expiration of the auth token.

Currently, the issue is that I am getting invalid credentials error and I believe it is because of expiration of auth token. I am not aware about the solution in this case. It is the sample code provided by Google and I believe it automatically handles Oauth authorization (unlike the case where we programmatically call an Oauth url, get a token, store it somewhere and provide it with our subsequent requests). What do I need to do with the sample code so as to resolve this and not to run into the error in future?

Also that the application is running fine locally, but the authorization issue comes when it is deployed on the cloud. Thanks.

Answer 1

Waitting for answers