java.io.IOException: The Application Default Credentials are not available - google-cloud-platform

Question

I am fairly new to GCP API functions.
I am currently trying to the use text-to-speech module following these steps: https://cloud.google.com/text-to-speech/docs/libraries
I did not set up the environmental variable since I used the authExplicit(String jsonPath) for its authentication: https://cloud.google.com/docs/authentication/production
my code looks like following;
public void main() throws Exception {
String jsonPath = "/User/xxx/xxxx/xxxxxx/xxxx.json";
authExplicit(jsonPath);
//calling the text-to-speech function form the above link.
text2speech("some text");
}
authExplicit(jsonPath) goes through without any problem and prints a bucket. I thought the credential key in JSON was checked. However, text2speech function returns the error as follows:
java.io.IOException: The Application Default Credentials are not available. They are available if running in Google Compute Engine. Otherwise, the environment variable GOOGLE_APPLICATION_CREDENTIALS must be defined pointing to a file defining the credentials. See https://developers.google.com/accounts/docs/application-default-credentials for more information.
I want to get the text2speech function work by call Google Cloud API functions.
Please let me know how to solve this issue.
Your advice would be highly appreciated.

Answer 1

It's confusing.
Application Default Credentials (ADC) is a process that looks for the credentials in various places including the env var GOOGLE_APPLICATION_CREDNTIALS.
If GOOGLE_APPLICATION_CREDNTIALS is unset and the code is running on a Google Cloud Platform (GCP) Compute Engine (GCE) service (e.g. Compute Engine), then it use the Metadata service to determine the credentials. If not, ADC fails and raises an error.
Your code fails because, authExplicit does not use ADC but loads the Service Account key from the file and creates a Storage account client using these credentials. Only the Storage client is thus authenticated.
I recommend a (simpler) solution: Use ADC and have Storage and Text2Speech clients both use ADC.
You will need to set the GOOGLE_APPLICATION_CREDENTIALS env var to the path to a key if you run your code off GCP (i.e. not on GCE or similar) but when it runs on GCP, it will leverage the service's credentials.
You will need to create both the Storage and Text2Speech clients to use ADCs:
See:
Cloud Storage
Text-to-Speech
Storage storage = StorageOptions.getDefaultInstance().getService();
...
And:
TextToSpeechClient textToSpeechClient = TextToSpeechClient.create()
...