Textract StartDocumentTextDetection

I have used the synchronous version of the textract api without a problem. And now trying the async version.

1. Feedback : The API seems to expect the request to be uploaded with content-type as multipart/form-data but I cannot see this mentioned in the documentation. Would suggest an update to the documentation to this effect.
2. Problem : I am using the same 'signing' logic as used for the sync function call but I get an error . x-amz-content-sha256 must be UNSIGNED-PAYLOAD, STREAMING-UNSIGNED-PAYLOAD-TRAILER, STREAMING-AWS4-HMAC-SHA256-PAYLOAD, STREAMING-AWS4-HMAC-SHA256-PAYLOAD-TRAILER, STREAMING-AWS4-ECDSA-P256-SHA256-PAYLOAD, STREAMING-AWS4-ECDSA-P256-SHA256-PAYLOAD-TRAILER or a valid sha256 value The http status code returned is 400.

I have computed the hash value of the entire content being POST-ed.

Even if I compute the hash value of the request alone, I get the same error.

Could you provide any link to the documentation which explains how this data is to the POST-ed. Or could you suggest how it is to be done.

I am not using the AWS SDKs and would prefer not to for certain customer specific considerations.

Thanks Kimman

Sample data POST-ed.

Content-Type: multipart/form-data X-Amz-Target: Textract.StartDocumentTextDetection X-Amz-Content-Sha256: e9f823f830156d0fd7d5eb6f99dd5194a1407206a0e3e88cbd13b4b2c4350091 Content-Length: 580 X-Amz-Date: 20230223T054757Z Host: textract.ap-south-1.amazonaws.com Authorization: AWS4-HMAC-SHA256 Credential=AKIAUKQ7DYLA4QD54GHV/20230223/ap-south-1/textract/aws4_request, SignedHeaders=content-length;content-type;host;x-amz-content-sha256;x-amz-date;x-amz-target, Signature=2a3f334d2acc53696d887a59eb2277f7ca0caf68cbf932fbe3f7837d6818c2d0