title: gmailr credentials randomly (?) need re-authentication
body: <p>I'm using <code>gmailr</code> in an automatic R script to send out some emails. It's been working fine for about a month and a half, but recently it failed with the following error:</p>
  <pre><code>Error: Can't get Google credentials.
  Are you running gmailr in a non-interactive session? Consider:
    * Call `gm_auth()` directly with all necessary specifics.
  Execution halted
  </code></pre>
  <p>My code, which hasn't changed, is</p>
  <pre><code>library(gmailr)
  options(gargle_oauth_email = TRUE)
  gm_auth_configure(path =&quot;data/credentials.json&quot;)
  gm_auth(email = TRUE, cache = &quot;.secret&quot;)
  </code></pre>
  <p>and is run non-interactively. (there is only one token in the <code>.secrets</code> folder) When I now ran it interactively, it &quot;did the dance&quot; and opened up the authentication thingy in the browser, which I confirmed and now everything is running fine again.</p>
  <p>The problem is that I don't understand why the credentials suddenly required re-authentication or how I could prevent the script failing like this in the future.</p>