Getting MissingAuthenticationTokenException for Polly.synthesizeSpeech with node.js sdk

Question

Hello! 
I'm getting MissingAuthenticationTokenException error for basic invocation.
Maybe i do something stupid?

```
import { Polly } from "@aws-sdk/client-polly";
assert(process.env.AWS_POLLY_REGION)
polly = new Polly({ region: process.env.AWS_POLLY_REGION });
const params = {
        OutputFormat: "ogg_vorbis",
        Text:"hello world",
        VoiceId: "Maxim",
};
const { AudioStream } = await polly.synthesizeSpeech(params);
```

Configured for polly permission:
```
{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": [
                "polly:SynthesizeSpeech"
            ],
            "Resource": "*"
        }
    ]
}
```
Any other services like sqs or dynamodb works well.

Accepted Answer

The error usually happens because the request must contain either a valid (registered) Amazon Web Services access key ID or X.509 certificate. 
https://docs.aws.amazon.com/AWSJavaSDK/latest/javadoc//index.html?com/amazonaws/services/computeoptimizer/model/MissingAuthenticationTokenException.html

For further insights, please take a look on this documentation and let me know if you still face an issue : 
https://docs.aws.amazon.com/sdk-for-javascript/v3/developer-guide/polly-examples.html

Getting MissingAuthenticationTokenException for Polly.synthesizeSpeech with node.js sdk

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