Q:

gmail api oauth two accounts possible issue

I have been working on a grails demo site which covers various methods of using gmail api mail plugin to send emails using standard,multiple To recipients, html emails, inline image(s). 
As well as a method to override or use different gmail accounts. This can all be found here 
Whilst doing the tests I noticed a strange behaviour with oauth, it is explained on the bottom of the README on that provided link

Unsure about this bit a little confusing as to how it works. lets say
  I generated client_secret.json under gmail account username Bob When
  for the very first email that needs to be confirmed via this site on a
  given account a one off process. During that 1 off process if i log in
  to gmail with another account of Bill The key is verified and emails
  then appear to come from bill@gmail.com Even though I had not visited
  / configured Bill's account to use the client_secret.json file.

So in short if I generate a secret.json file from account1, when sending the very first email from that account. If I happen to be logged in from account2. The storedCredentials file generated by google (there on) the 'me' account becomes my 2nd account. Even though everything to generate the key etc was done on account1. 
Does it make sense is this normal behaviour or a bug ?

A:

The client_secret.json file only needs to be generated once per application. It is how the application identifies itself to Google, and generating it does not grant any API access to any accounts. The same client secrets file is used to perform the OAuth flow for all the users that want to grant the application access to their data.

