Q:

AWS Transcribe Error: Unable to determine service/operation name to be authorized

After a series of longs hours working with AWS transcription, I now have a new error using Postman:
<AccessDeniedException>
  <Message>Unable to determine service/operation name to be authorized</Message>
</AccessDeniedException>

However, I don't know what the issue is. I tried to Google it but the error seems to happen also in AWS Lambda. But I'm working with AWS Transcription. Can anyone check what seems to be the problem?
My sample sample GET request is:
https://transcribestreaming.us-east-1.amazonaws.com/medical-stream-transcription-websocket?X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=MYACCESSKEYID%2F20200404%2Fus-east-1%2Ftranscribe%2Faws4_request&X-Amz-Date=20200404T171802Z&X-Amz-Expires=300&X-Amz-SignedHeaders=host&language-code=en-US&media-encoding=pcm&sample-rate=16000&specialty=PRIMARYCARE&type=DICTATION&X-Amz-Signature=5f5f0a5d336e524b335245b6e83945d3057ec3905a9ae2d2ca709b77cce5478f

I intentionally replace the X-Amz-Credential with MYACCESSKEYID for security purpose.

A:

There maybe two errors:
1) "https://" request connects to default port of 443. This cause error of "Unable to determine service/operation name to be authorized". Please explicitly use port :8443.
2) Your client does not handle websocket upgrade correctly. In the first request to open connection, your client need initiate websocket upgrade by including several headers, as specified in "Including WebSocket Request Headers" section of https://docs.aws.amazon.com/transcribe/latest/dg/websocket-med.html#websocket-response-med
Example in curl: 
curl --include --no-buffer \
--header "Connection: Upgrade" \
--header "Upgrade: websocket" \
--header "Host: transcribestreaming.us-east-1.amazonaws.com:8443" \
--header "Origin: http://localhost:3000" \
--header "Sec-WebSocket-Key: tEfHvBSx8jqQyZgCNrhI3w" \
--header "Sec-WebSocket-Version: 13" \
"https://transcribestreaming.us-east-1.amazonaws.com:8443/medical-stream-transcription-websocket?X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=MYCREDENTIAL&X-Amz-Date=20200406T211542Z&X-Amz-Expires=60&X-Amz-Signature=MYSIGNATURE&X-Amz-SignedHeaders=host&language-code=en-US&media-encoding=pcm&sample-rate=16000&specialty=PRIMARYCARE&type=DICTATION"

On a successful request, client receive "101 Switching Protocols". The connection is established, and then you can continue send audio frames as documented in https://docs.aws.amazon.com/transcribe/latest/dg/websocket-med.html#websocket-streaming-request-med

