Google speech to text authentication access token expiry issue - google-cloud-platform

Question

I am using google speech to text api and followed all the steps mentioned in below link :
https://cloud.google.com/speech/docs/getting-started
When I used the commands using command line interface mentioned in above page, everything seems fine and I am getting the output text as well.
But, if I create a php file for the same commands then it is working fine for 1 hour and then the token expires. And also not creating the token with below command via php file :
shell_exec(gcloud auth activate-service-account --key-file=/keyfile.json)
shell_exec(gcloud auth print-access-token)
But the same command is working very fine on command line system.
So basically I am having issue with the authentication process via php file and getting the below error :
"error": { "code": 401, "message": "Request had invalid authentication credentials.", "status": "UNAUTHENTICATED" } }
Can anyone please tell what I am missing or am I following the wrong approach for authentication?

Answer 1

Reproduced successfully and ran again the php file after one hour and then 2 hours with the same result: no errors. You may consider providing more detail, maybe by including directives such as ini_set('display_errors', 'On'); error_reporting(E_ALL); in your file.
A relevant read about the on-hour expiry of credentials is to be found at [1], in the 401-error sub-chapter.
[1] https://cloud.google.com/storage/docs/xml-api/reference-status